This section covers recordable CD media.


Subject: [7-1] What kinds of media are there?
(2004/02/17)

The basic building blocks of CD-R media are organic dye and a reflective
layer.  The dye types currently in use are:

	- cyanine dye, which is cyan blue in color (hence the name);
	- phthalocyanine and "advanced" phthalocyanine dye, which have
	  a faint aqua tinge;
	- metalized azo, which is dark blue.

In addition, Kodak has patented a "formazan" dye, which is light green.
This has been reported to be a hybrid of cyanine and phthalocyanine.

The reflective layer is either a silver alloy, the exact composition of
which is proprietary, or 24K gold.  Aluminum isn't used in CD-R media
because the metal reacts with the dyes.

Discs come in many different colors.  The color you see is determined by
the color of the reflective layer (gold or silver) and the color of the dye
(light blue, dark blue, green, or colorless).  For example, combining a
gold reflective layer with cyanine (blue) dye results in a disc that is
gold on the label side and green on the writing side.

Many people have jumped to the conclusion that "silver" discs are made with
pure silver, and have attempted to speculate on the relative reflectivity
and lifespan of the media based on that assumption.  According to one source,
silver is susceptible to corrosion when exposed to sulfur dioxide (a common
air pollutant), so manufacturers use alloys of silver to inhibit corrosion.

Taiyo Yuden produced the original gold/green CDs, which were used during the
development of CD-R standards.  Mitsui Toatsu Chemicals invented the process
for gold/gold CDs.  Mitsubishi's NCC subsidiary developed the metalized azo
dye.  Silver/blue CD-Rs, manufactured with a process patented by Verbatim,
first became widely available in 1996.  According to the Ricoh web site,
the silver/silver "Platinum" discs, based on "advanced phthalocyanine dye",
were introduced by them in 1997.  They didn't really appear on the market
until mid-1998 though.  Kodak Japan holds the patent on formazan dye.

One reason why there are multiple formulations is that the materials and
processes for each are patented.  If a new vendor wants to get into the
CD-R market, they have to come up with a new combination of materials that
conforms to the Orange Book specifications.

Some CDs have an extra coating (e.g. Kodak's "Infoguard") that makes the CD
more scratch-resistant, but doesn't affect the way information is stored.
The top (label) side of the CD is the part to be most concerned about,
since that's where the data lives, and it's easy to damage on a CD-R.
Applying a full circular CD label will help prevent scratches.

An EMedia Professional article discussing the composition of the newer
discs is online at http://www.emediapro.com/EM1998/starrett10.html.

CD-RW discs have an entirely different composition.  The data side
(opposite the label side) is a dark silvery gray that is difficult to
describe.


Subject: [7-2] Does the media matter?
(2001/07/16)

Yes.  There are four factors to consider:

  (1) Does it work with your recorder?
  (2) Which CD readers can use it?
  (3) How long does it last before it starts to decay?
  (4) What's the typical BLER (BLock Error Rate) for the media?

Some audio CD players (like the ones you'd find in a car stereo) have
worked successfully with one brand of media but not another.  There's
no "best" kind, other than what works the best for you.

Some people have found brand X CD-R units work well with media type Y,
while other people with the same unit have had different results.
Recording a disc at 4x may make it unreadable on some drives, even though
a disc recorded at 2x on the same drive works fine.

To top it all off, someone observed that discs burned with one brand of
CD-R weren't readable in cheap CD-ROM drives, even though the same kind
of media burned in a different device worked fine.  The performance of
any piece of media is always a combination of the disc, the drive that
recorded it, and the drive that reads it.

A number of specific discoveries have been posted to Usenet, but none of
them are conclusive.  Many people have reported that Kenwood CD players
don't deal with CD-Rs very well, while Alpine units play nearly
everything.  However, things change as product lines evolve over time.

Some users have found that the *quality* of audio recordings can vary
depending on the media.  Whatever the case, if you find that CD-Rs don't
sound as good as the originals, it's worthwhile to try a different kind of
media or a different player.  See section (4-18) for other ideas.

If you want to see what media test results look like, take a look at
http://www.digit-life.com/articles/cdrdisktest/index2.html.

One final comment: while there are clearly defined standards for CD-R
media, there are no such standards for CD and CD-ROM drives -- other than
that they be able to read CDs.  It is possible for media to be within
allowed tolerances, but be unreadable by a CD-ROM drive that can handle
pressed discs without trouble.  All you can do in this sort of situation is
find a better-quality CD or CD-ROM drive, or switch to a brand of media
whose characteristics are on the other side of the tolerance zone.


Subject: [7-3] Who manufactures CD-R media?
(2000/09/03)

Taiyo Yuden made the first "green" CDs.  They are now manufactured by TDK,
Ricoh, Kodak, and probably several others as well.

Mitsui Toatsu Chemicals (MTC) made the first "gold" CDs.  They are now
manufactured by Kodak and possibly others as well.

Verbatim made the first "silver/blue" CDs.

Most CD-R brands (e.g. Yamaha and Sony) are actually made by a handful of
major disc manufacturers.  Attempting to keep track of who makes what is
a difficult proposition at best, since new manufacturing plants are being
built, and resellers can switch vendors.  See section (2-33) for notes
about identifying the source of a CD-R.


Subject: [7-4] Which kind of media should I use?
(2003/07/11)

There is no "best" media for all recorders.  You can't tell how well a disc
will work just by looking at it; the only way to know is to put it in
*your* recorder, write a disc, then put it in *your* reader and try it.
Statements to the effect that "dark green" is better than "light green" are
absurd.  Some discs are more translucent than others, but that doesn't
matter: they only have to reflect light in the 780nm wavelength, not the
entire visible spectrum.  See (7-19).

It's probably a good idea to start by selecting media that is certified
for your recorder's desired write speed.  See section (3-31) for some
other remarks about recording speed.

Speed considerations are more important for CD-RW than CD-R.  Many drives
refuse to record at speeds higher than the disc is rated for.  On top of
that, there are "ultra speed +" blanks (for 32x recording), "ultra speed"
blanks (for 8x-24x), "high speed" blanks (for 4x-10x) and "standard" blanks
(for 1x-4x).  The faster blanks are labeled with a "High Speed CD-RW" or
"Ultra Speed CD-RW" logo, and will not work in older drives.

The Orange Book standard was written based on the original "green" cyanine
discs from Taiyo Yuden.  Cyanine dye is more forgiving of marginal read/write
power variations than "gold" phthalocyanine dye, making them easier to
read on some drives.  On the other hand, phthalocyanine is less sensitive
to sunlight and UV radiation, suggesting that they would last longer under
adverse conditions.

Manufacturers of phthalocyanine-based media claim it has a longer lifespan
and will work better in higher speed recording than cyanine discs.
See http://www.cd-info.com/CDIC/History/Commentary/Parker/stcroix.html
for some notes on low-level differences between media types.

There is no advantage to using expensive "audio CD-Rs" or "music blanks".
There is no difference in quality between consumer audio blanks and standard
blanks from a given manufacturer.  If you have a consumer audio CD recorder,
you simply have no other choice.  There is no way to "convert" a standard
blank into a consumer audio blank.  See section (5-12) for notes on how
you can trick certain recorders into accepting standard blanks.

Trying samples of blanks is strongly recommended before you make a major
purchase.  Remember to try them in your reader as well as your writer; they
may not be so useful if you can't read them in your normal CD-ROM drive.

Maxell's CD-R media earned a miserable reputation on Usenet.  In April
'97 Maxell announced reformulated media that seemed to work better than
the previous ones.  It appears they may no longer make their own media.

Some good technical information is available from http://www.mscience.com/.
In particular, "Are green CD-R discs better than gold or blue ones?" at
http://www.mscience.com/faq52.html.

BLER measurements for a variety of recorders and media is in a big table
on http://www.digido.com/meadows.html.

See also "Is There a CD-R Media Problem?" by Katherine Cochrane, originally
published in the Feb '96 issue of CD-ROM Professional.


Subject: [7-4-1] What's the best brand of media?
(2003/07/08)

As noted in (7-4), there is no guarantee that brand X will be the absolute
best in recorder Y.  However, some brands are recommended more often
than others.  It does pay to be brand-conscious.

Brands most often recommended: Mitsui, Kodak, Taiyo Yuden, and TDK.
Sometimes Pioneer and Ricoh.  It appears that HP, Philips, Sony, Yamaha,
and Fuji use these manufacturers for most of their disks.  (Kodak no longer
manufactures media.)

Brands that are often trashed: Maxell, Verbatim, Memorex, Ritek, Hotan,
Princo, Gigastorage, Lead Data, Fornet, CMC Magnetics.  Many "no-name"
bulk CD-Rs are one of these brands.

Sometimes a particular line of discs from a particular manufacturer or
reseller will be better than others from the same company.  For example,
Verbatim DataLifePlus discs are recognized as pretty good, but Verbatim
ValuLife are seen as being of much lower quality.

Sometimes company names change.  For example, in June 2003 Mitsui Advanced
Media was purchased from Mitsui Chemicals by Computer Support Italcard
(CSI) of Italy to form MAM-A, Inc.

The country of manufacture may also be significant.  Some manufacturers
maintain plants in different countries, and don't always maintain the same
level of quality.

In humid tropical climates, care must be taken to find discs that stand up
to the weather.  One user reported that the data layer on Sony CDQ 74CN
discs began cracking after a couple of months in an otherwise sheltered
environment (e.g. no direct sunlight).  Mitsubishi CD-R 700 and Melody 80
Platinum discs fared much better.


Subject: [7-5] How long do CD-Rs and CD-RWs last?
(2005/04/14)

CD-RWs are expected to last about 25 years under ideal conditions (i.e. you
write it once and then leave it alone).  Repeated rewrites will accelerate
this.  In general, CD-RW media isn't recommended for long-term backups or
archives of valuable data.

The rest of this section applies to CD-R.

The manufacturers claim 75 years (cyanine dye, used in "green" discs), 100
years (phthalocyanine dye, used in "gold" discs), or even 200 years
("advanced" phthalocyanine dye, used in "platinum" discs) once the disc has
been written.  The shelf life of an unrecorded disc has been estimated at
between 5 and 10 years.  There is no standard agreed-upon way to test discs
for lifetime viability.  Accelerated aging tests have been done, but they
may not provide a meaningful analogue to real-world aging.

Exposing the disc to excessive heat, humidity, or to direct sunlight will
greatly reduce the lifetime.  In general, CD-Rs are far less tolerant of
environmental conditions than pressed CDs, and should be treated with
greater care.  The easiest way to make a CD-R unusable is to scratch the
top surface.  Find a CD-R you don't want anymore, and try to scratch the
top (label side) with your fingernail, a ballpoint pen, a paper clip, and
anything else you have handy.  The results may surprise you.

Keep them in a cool, dark, dry place, and they will probably live longer
than you do (emphasis on "probably").  Some newsgroup reports have
complained of discs becoming unreadable in as little as three years, but
without knowing how the discs were handled and stored such anecdotes are
useless.  Try to keep a little perspective on the situation: a disc that
degrades very little over 100 years is useless if it can't be read in your
CD-ROM drive today.

One user reported that very inexpensive CD-Rs deteriorated in a mere six
weeks, despite careful storage.  Some discs are better than others.

An interesting article by Fred Langa (of http://www.langa.com/) on
http://www.informationweek.com/story/showArticle.jhtml?articleID=15800263&pgno=1
describes how to detect bad discs, and discusses whether putting an adhesive
label on the disc causes them to fail more quickly.

By some estimates, pressed CD-ROMs may only last for 10 to 25 years,
because the aluminum reflective layer starts to corrode after a while.

One user was told by Blaupunkt that CD-R discs shouldn't be left in car CD
players, because if it gets too hot in the car the CD-R will emit a gas that
can blind the laser optics.  However, CD-Rs are constructed much the same
way and with mostly the same materials as pressed CDs, and the temperatures
required to cause such an emission from the materials that are exposed would
melt much of the car's interior.  The dye layer is sealed into the disc,
and should not present any danger to drive optics even if overheated.
Even so, leaving a CD-R in a hot car isn't good for the disc, and will
probably shorten its useful life.

See also http://www.cd-info.com/CDIC/Technology/CD-R/Media/Longevity.html,
especially http://www.cd-info.com/CDIC/Industry/news/media-chronology.html
about some inaccurate reporting in the news media.

See "Do gold CD-R discs have better longevity than green discs?" on
http://www.mscience.com/faq53.html.

There's a very readable discussion of CD-R media error testing on
http://web.archive.org/web/20031211151723/http://www.cdpage.com/dstuff/BobDana296.html
that leaves you with a numb sense of amazement that CD-Rs work at all.
It also explains the errors that come out of MSCDEX and what the dreaded
E32 error means to a CD stamper.

An interesting document entitled "Care and Handling of CDs and DVDs -
A Guide for Librarians and Archivists" can be found on the web sites
for the National Institute of Standards and Technology (NIST) and the
Council on Library and Information Resources (CLIR).  View it on the web
at http://www.clir.org/pubs/reports/pub121/contents.html or as a PDF from
http://www.itl.nist.gov/div895/carefordisc/CDandDVDCareandHandlingGuide.pdf.
It has a wealth of information about disc composition and longevity,
as well as recommendations for extending the lifespan of your media.

Another good NIST article, "Stability Comparison of Recordable Optical
Discs -- A Study of Error Rates in Harsh Conditions" can be found at
http://www.itl.nist.gov/div895/gipwg/StabilityStudy.pdf.


Kodak has some interesting information about their "Ultima" media.
See http://www.kodak.com/global/en/service/cdrMedia/index.jhtml,
specifically the "KODAK Ultima Lifetime Discussion" and "KODAK Ultima
Lifetime Calculation" white papers (currently in PDF format).  The last page
discusses the Arrhenius equation, which is used in chemistry to calculate
the effect of temperature on reaction rates.  The Kodak page defines it as:

  t = A * exp(E/kT)

where 'exp()' indicates exponentiation.  't' is disc lifetime, 'A' is a
time constant, 'E' is activation energy, 'k' is Boltzmann's constant, and
'T' is absolute temperature.  The equation allows lifetime determined at
one temperature to be used to establish the lifetime at another.  If a
disc breaks down in three months in extreme heat, you can extrapolate the
lifetime at room temperature.

The trouble with the equation is that you have to know either 'A' or 'E'.
It appears that 'A' can be estimated based on empirical evidence, but see
http://palimpsest.stanford.edu/byorg/abbey/an/an23/an23-3/an23-308.html
for some cautions about how tricky it can be to choose the right value.


Subject: [7-6] How much data can they hold?  650MB?  680MB?
(2004/04/15)

There are 21-minute (80mm/3-inch), 74-minute, 80-minute, 90-minute, and
99-minute CD-Rs.  These translate into data storage capacities of 184MB,
650MB, 700MB, 790MB, and 870MB respectively (see below for exact figures).
See section (7-14) for more about 80mm CD-Rs, and sections (3-8-1) and
(3-8-2) for notes on 80-, 90-, and 99-minute blanks.  There used to be
63-minute CD-Rs, but these have largely vanished.

Typical 74-minute CD-Rs are advertised as holding 650MB, 680MB, or even
700MB of data.  The reality is that they're all about the same size, and
while you may get as much as an extra minute or two depending on the exact
construction, you're not usually going to get an extra 30MB out of a disc
labeled as 74-minute media.  See section (3-8-3) for information on writing
beyond a disc's stated capacity.

Folks interested in "doing the math" should note that only 2048 bytes of
each 2352-byte sector is used for data on typical (Mode 1) discs.  The rest
is used for error correction and miscellaneous fields.  This is why you can
fit 747MB of audio WAV files onto a disc that holds 650MB of data.

It should also be noted that hard drive manufacturers don't measure megabytes
in the same way that RAM manufacturers do.  The "MB" for RAM means 1024x1024,
but for hard drives it means 1000x1000.  A data CD that can hold 650 "RAM"
MB of data holds about 682 "disk" MB of data, which is why many CD-Rs
are mislabeled as having a 680MB capacity.  (The notion of "unformatted
capacity" is a nonsensical myth stemming from early hard drives.)

Spelled out simply:

  21 minutes ==  94,500 sectors == 184.6MB CD-ROM == 212.0MB CD-DA
  63 minutes == 283,500 sectors == 553.7MB CD-ROM == 635.9MB CD-DA
  74 minutes == 333,000 sectors == 650.3MB CD-ROM == 746.9MB CD-DA
  80 minutes == 360,000 sectors == 703.1MB CD-ROM == 807.4MB CD-DA
  90 minutes == 405,000 sectors == 791.0MB CD-ROM == 908.4MB CD-DA
  99 minutes == 445,500 sectors == 870.1MB CD-ROM == 999.3MB CD-DA

The International Electrotechnical Commission (IEC) has approved alternate
prefixes for binary powers of two.  Instead of kilobytes and megabytes
we would call them kibibytes and mebibytes, with KiB and MiB replacing
KB and MB.  This means an 80-minute CD would be rated as holding 703.1MiB
or 737.3MB.  These haven't yet fallen into common usage.  Check the NIST
site for full details: http://physics.nist.gov/cuu/Units/binary.html.

Many CD recording programs will tell you the exact number of 2K sectors
available on the CD.  This is the only reliable way to know exactly
how many sectors are available.  99-minute blanks will actually report
incorrect values.

An informal survey conducted by one user found that the deviation between the
largest and smallest 74-minute CD-R was about 3500 sectors (47 seconds, or
7MB), which while not inconsequential is nowhere near the difference between
650MB and the 680MB or 700MB figures quoted by some manufacturers.  All discs
had at least 333,000 sectors, as required by the Red Book specification.

http://www.cdmediaworld.com/ has a fairly detailed listing of how much
data different brands of media will actually hold.  Again, bear in mind
that different batches of the same media may have different capacities.

The PCA (Power Calibration Area), PMA (Program Memory Area), TOC (Table
of Contents), lead-in, and lead-out areas don't count against the time
rating on single-session CDs.  You really do get all the storage that the
disc is rated for.  On standard MODE 1 discs that aren't using packet
writing, there is no "formatting overhead".  Bear in mind, however, that
the "cluster" size is 2K, and that the ISO-9660 filesystem may use more or
less space than an MS-DOS FAT or HFS filesystem, so 650MB of files on a
hard disk may occupy a different amount of space on a CD.

On a multisession disc, you lose about 23MB of space when the first session
is closed (to pave the way for the 2nd session), and about 14MB for each
subsequent session.  A common mistake when writing multisession CDs is to
overestimate the amount of space that will be available for future sessions,
so be sure to take this into account.

(If you want the details: the first additional session requires 4500 sectors
for the lead-in and 6750 for the lead-out, for a total of 11250 (22.5MB,
or 2.5 minutes).  Each additional session requires 4500 for the lead-in
and 2250 for the lead-out, for a total of 6750 (13.5MB, or 1.5 minutes).
You may also need to factor 2-second pre-gaps into the size calculation
for each session.  On a single-session disc, the overhead for lead-in
and lead-out are not counted as part of the user data area, so nothing is
"lost" until you go multisession.)

Pressed aluminum CDs are also supposed to hold no more than 74 minutes of
audio, but are often tweaked to hold more (see section (3-8)).  To convert
sectors back to seconds, divide the number of sectors by 75.  If your blanks
have 333,000 sectors, they have 4440 seconds, which is exactly 74 minutes.

Some packet-writing solutions will take a large bite out of your available
disc space.  For example, if you use Roxio DirectCD 2.x with CD-RW media,
it uses fixed-length packets.  This allows random file erase, which means
that when you delete a file you actually get the space back, but you're
reduced to about 493MB after formatting the disc.  More recent versions can
get closer to 531MB.  See section (4-42) for more info.


Subject: [7-7] Is it okay to write on or stick a label on a disc?
(2006/12/10)

It depends.  Use the right kind of pen and you shouldn't have a problem.
With labels the situation is a little less certain.

Keep in mind that the data is essentially stored on the top (label side) of
the disc.  If you damage the top, your data or music is permanently gone.
See section (2-1) for a description of the physical makeup of a disc.


Subject: [7-7-1] Can I write on them?  What kind of pen should I use?
(2006/12/10)

The ink in some permanent markers can eat away the lacquer coat, which
will cause your disc to become unreadable very quickly.  Some discs are
more vulnerable than other.  Unless the disc has some sort of protective
top coat (such as a printable surface), always use pens specifically
designated as safe for CD-R.

Never write on a disc with a ball-point pen.  Pressing down on the label
side could pierce or deform the reflective layer.

Examples of pens for CD-Rs include the Dixon Ticonderoga "Redi Sharp
Plus", the Sanford "Powermark", and TDK "CD Writer".  Some of these are
relabeled Staedtler Lumocolor transparency markers (#317-9), which are
alcohol-based.  Never use a solvent-based "permanent" marker on a CD-R --
it can eat through the lacquer coat and destroy the disc.  Memorex sells
water-based color "CD Markers" in four-packs (black, blue, red, green).

Many people have had no problems with the popular Sanford "Sharpie" pens,
which are alcohol-based.  Other people say they've damaged discs by writing
on them with a Sharpie, though those discs may have been particularly
susceptible.  The official word from Sanford is:

  "Sanford has used Sharpie Markers on CDs for years and we have never
  experienced a problem.  We do not believe that the Sharpie ink can
  affect these CDs, however we have not performed any long-term
  laboratory testing to verify  this.  We have spoken to many major CD
  manufacturers about this issue.  They use the Sharpie Markers on CDs
  internally as well, and do not believe that the Sharpie Ink will cause
  any harm to their products.

  [...]

  Sanford Consumer Affairs"

In any event, the Ultra Fine Sharpie pen looks almost sharp enough to
scratch, so sticking with the Fine Point pen is recommended.

So long as you use the right kind of pen, it's okay to write directly on
the top surface of the CD, label or no.  Use a light touch -- you aren't
filling out a form in triplicate.  If the prospect makes you nervous,
just write in the clear plastic area near the hub.


Subject: [7-7-2] Are labels okay?
(2006/12/10)

The adhesives on some labels can dissolve the protective lacquer coating
if the adhesive is based on a solvent that the lacquer is susceptible to.
Asymmetric labels can throw the disc out of balance, causing read problems,
and labels not designed for CDs might bubble or peel off when subjected
to long periods of heat inside a CD drive.  Always use labels designed
for CD-R media.

There is evidence that labels can shorten CD-R lifetime, so it might be
best to label data archives and backups with a pen instead (see section
(7-5) for more).  Adhesive labels aren't recommended for discs you plan
to keep for more than five years.

The best way to feel confident about labeling your discs is to try it
yourself.  Buy some labels, put them on some discs, leave them someplace
warm, and see if they peel off.  If they do, you'll need a different
kind of media or a different kind of label.  Some labels don't adhere
very well unless they're attached to a disc with a plain lacquer surface
on top, so combining labels with "inkjet printable surface" media may be
asking for trouble.  One note of caution: this only tells you if the label
will peel up right away.  It doesn't tell you if the label will still be
nice and flat two or three years from now, especially if you live in the
tropics where the air is always hot and damp.

Whatever you do, don't try to peel a label off once it's on.  You will
almost certainly pull part of the recording layer off with the label.  If
you're going to label a disc, do it immediately, so you can make another
copy if the label doesn't adhere smoothly.  Any air bubbles in the label
that can't be smoothed out immediately are going to cause trouble.  Use
a label applicator for best results.

It may not be a good idea to put labels on discs that will be fed into a
"slot in" CD player, such as those popular in dashboard car CD players.
Sometimes the added thickness will cause the disc to get stuck, or the
edge will peel up when the motor grabs it.

A number of companies make labels for CDs, and some sell complete kits
including applicators and software.  Two of the biggest are NEATO, at
http://www.neato.com/, and CD Stomper, at http://www.cdstomper.com/.
The software from http://www.surething.com/ includes templates for a
variety of different label layouts.  Medea International sells labels and
labeling software; see http://www.medea.co.uk/pressit/.  Check section
(8-3) for other sources.

If you want a label that also covers up the clear plastic part at the
center of the disc, search for "hub labels".  There are even labels that
*only* cover the hub section.

For information about printing directly onto the surface of a disc,
see section (7-29).

Some information on CD-R labeling options can be found here:
http://www.cd-info.com/CDIC/Technology/CD-R/Labeling/

Sony's http://www.sonydadc.com/ web site has a "Downloads & Templates"
section with artwork that my prove useful.  You can find most CD-related
logos on the site (try http://www.sonydadc.com/downloads/, scroll
down to "Logos" for common formats).  Some are also available from
http://www.licensing.philips.com/cdsystems/cdlogos.html.

Mike Richter's CD-R primer has a very nice page on labeling discs.  See
http://www.mrichter.com/cdr/primer/labels.htm.

It is important to keep the CD balanced, or high-speed drives may have
trouble reading the disc.  According to one report, a disc that had a
silk-screened image on the left side of a CD-R (leaving the right half of
the disc blank) was unreadable on high-speed drives due to excessive
wobbling.  Most label kits come with a label-centering device, usually
something trivial like a stick that's the same width as the hole in the
middle of the CD.

Avery's CD-R labels became quietly unavailable in October 1997.  The rumor
is that the adhesive caused data corruption problems, so Avery recalled
them.  There are indications that the adhesive would fail on some discs
and start to lift off within a short period of time.  If you have Avery
labels (#5824) purchased before this date, you should avoid using them.
The labels being produced now don't have this problem.


Subject: [7-8] How do CD-Rs behave when microwaved?
(2001/09/19)

Disclaimer: I'm not recommending you put a CD into a microwave.  CDs may
contain metals that will cause your microwave to arc, destroying the
microwave emitter (see cautions about metal objects in the manual for your
microwave).  Don't try this at home.  Better yet, don't try this at all.

The basic process is, take a disc that you don't want anymore, and put
it shiny-side-up on something like a coffee mug so it's nowhere near the
top, bottom, or sides of the microwave.  (Actually, you may want to leave
it right-side-up if the disc doesn't have a label, because the foil is
closest to the top of the CD.)  I'm told it is important to put something
in the cup to be on the safe side, so fill it most of the way with water.
Try to center it in the microwave.  Turn off the lights.  Program the
microwave for a 5-second burst on "high", and watch the fireworks.

Performing this operation on replicated CDs results in blue sparks that
dance along the CD, leaving fractal-ish patterns etched into the reflective
aluminum.  For those of you not with the program, this also renders the CD
unreadable.

Trying this with a green/gold CD-R gives you a similar light show, but the
destruction patterns are different.  While pressed CDs and CD-RWs don't
develop consistent patterns of destruction, CD-Rs tend to form circular
patterns, possibly because of the pre-formed spiral groove.

On a different note, CD-Rs seem to smell worse, or at least they start to
smell earlier, than pressed CDs.  The materials used are non-toxic
("cyanine" comes from the color cyan, not from cyanide), but breathing the
fumes is something best avoided.

For the curious, here's a note about why they behave like they do:

  "The aluminum layer in a CD-ROM is very thin. The microwave oven induces
  large currents in the aluminum. This makes enough heat to vaporize the
  aluminum. You then see a very small lightning storm as electric arcs go
  through the vaporized aluminum. Within a few seconds there will be many
  paths etched through the aluminum, leaving behind little metalic islands.
  Some of the islands will be shaped so that they make very good microwave
  antennas. These spots will focus the microwave energy, and get very hot.
  Now you will see just a few bright spots spewing a lot of smoke. The good
  part of the light show is over, turn off the oven.

  I suspect that if you leave the oven going much longer, the CD-ROM will
  burst into flame. This will smell very bad and may do bad things to your
  oven and house. Don't do it."
  -- Paul Haas (paulh@hamjudo.com), on http://hamjudo.com/notes/cdrom.html

Dreamcast GD-R discs come out just like CD-R, but DVD-R is a whole
different experience.

Combining a microwaved CD-R with a tesla coil produces interesting results.
See http://www.electricstuff.co.uk/cdzap.html.


Subject: [7-9] What can I do with CD-R discs that failed during writing?
(2005/01/03)

If the disc wasn't closed, you can write more data in a new session.  If
the disc was closed, or was nearly full when the write failed but is still
missing important data, then its use as digital media is over.

However, that doesn't mean it's useless.  Here are a few ideas:

 - Fill in the center hole to avoid leaks, and use them as drink coasters.
 - Create a hanging ornament (suitable for holiday decorations) or wind
   chime.  The latter isn't all that interesting - they just sort of
   "clack" a little - unless you use the discs to catch the wind and
   something else to make the chimes.
 - Use them as mini-frisbees in an office with cubes.  Since they're rather
   solid and may hurt when they hit, you should await a formal declaration
   of intra-office war before opening up with these.
 - Have CD bowling tournaments where you see how far you can roll one down
   a narrow hallway.  You'd be surprised at how hard it can be unless you
   get the wrist motion just right.
 - Put them under a table or chair whose legs don't quite sit right.
 - Run them through one of those industrial-strength paper shredders (the
   kind with the rapidly spinning wheels) to get shiny green or gold
   confetti.
 - Make really, really big earrings.
 - Try to convince people at the beach that it's a shell from a new species
   of abalone.
 - Hook them into your bicycle spokes as reflectors.
 - Use them as wheels on a toy car.  (If you had buggy firmware, you're
   probably stocked for a toy 18-wheeler.)
 - Build a suit of "CD-R chain mail" for laser-tag games.
 - Use them as art-deco floor or ceiling tiles.
 - Hang them from the rear view mirror in your car.
 - Cut it into a jigsaw puzzle with a small wire saw.
 - Try out the "helpful CD repair" suggestions that periodically crop on
   the newsgroup.  Like the ones that suggest using acetone and sandpaper
   to refinish a scratched CD-R.
 - Hang them in your car windows.  Some people believe that CDs will defeat
   speed guns and automated speed traps that use flash photography.
 - Add them to your aquarium.
 - Use them as dart boards or BB-gun targets.  If you "miss" the hole in
   the middle, the error is immediately obvious.
 - String several together as a toy, weaving the string in and out through
   the center holes.  Alternate green and gold for visually pleasing results.
 - Make a boomerang (http://www.chez.com/amiel/boom/cd.html).
 - Buy a cheap clock mechanism from a hobby/electronics store, and turn
   it into a novelty clock.
 - Hang them in fruit trees to scare birds away.
 - Use them as backing for round knobs on cabinet doors, to keep the
   wood from getting soiled.  Works best with 80mm discs.
 - Practice applying CD labels.  Test brands of labels you haven't tried
   before.  Leave them in the sun and see if they peel.
 - Gripping the CD with two pairs of pliers, hold it over a small heat
   source, such as a small propane torch.  Keep it moving slightly so it
   doesn't scorch.  When the plastic reaches the melting point, stretch,
   twist, or bend the CD into something artistic.  (Do this in a well
   ventilated outdoor area with adult supervision!!)
 - Heat a penny with a propane torch or on the stove for a few seconds,
   holding it with a pair of pliers.  Push the penny through the center
   hole so it wedges halfway through.  The heat of the penny softens the
   polycarbonate, so once it cools it should stay put.  The discs are well
   balanced, and spin very nicely, especially when decorated with spiral
   patterns (http://jclahr.com/science/Illusions/fbkspin.html).
 - Use them as reflectors in a solar collector.

If you've given up hope of doing something "useful" with it, do something
destructive with it.  Try to scrape the reflective layer off the top with
your fingernail.  Drop it on the ground so that it hits edge-on and see
if the reflective layer delaminates or the plastic chips.  Try to snap it
in half.  Leave it sitting on a window sill with half the disc covered by
a book to see the effects of heat and sunlight.  Write on it with nasty
permanent markers and see if you can still read it a week later.  Apply a
CD label then pull it off again.  Different brands of media have different
levels of tolerance to abuse, and it's useful to understand just how much
or how little it takes to destroy a disc.

In one carefully controlled experiment it was determined that CD-Rs behave
differently from pressed CDs when you slam them edge-on against the
ground.  The aluminum ones will chip (once you throw them hard enough,
otherwise they just bounce) and create silver confetti.  The gold one I
tried chipped and the gold layer started peeling, leaving little gold
flakes everywhere.  One user reported that a Verbatim blue CD developed
bubbles even though the plastic was intact.  More experimentation is needed
(but not around pets, small children, or hard-to-vacuum carpets).

On a different tack, some CD-Rs don't hold up well when immersed in water.
Try pouring a little water on a disc, then let it sit until it dries.  If
the top surface scratches off more easily afterward, you need to be careful
around moisture.  Silver/blue Verbatim discs seem particularly sensitive.

One comment about snapping discs in half with your fingers: use caution.
Depending on the disc and how you break it, you may end up with lots of
sharp polycarbonate slivers flying through the air.  Wear eye protection,
be aware of people around you, and be sure to clean up all the plastic
shards afterward.

If you have far more coasters than you want to play with, consider recycling
them (section (7-21)).


Subject: [7-10] Where can I find jewel cases and CD sleeves?
(2004/01/12)

There are many vendors.  A few are listed below.

Incidentally, you have a lot of choices when it comes to CD packaging.
There are single-disc jewel cases, double-sized doubles, single-sized
doubles, triples, quads, sextuples, plain colors, neon colors, paper
envelopes, Tyvek envelopes, cardboard sleeves, clear jewel cases with black
trays, clear jewel cases with built-in trays, CD pockets for use in
three-ring binders, and on, and on.

If you can imagine it, it's probably up for sale.

Some URLs to start with:

  http://www.bagsunlimited.com/
  http://www.cdrom2go.com/
  http://www.xdr2.com/cd-jewel.htm
  http://www.cdroutlet.com/
  http://www.desktopsupplies.com/dps/cdromproducts.html
  http://www.discmarket.com/
  http://www.americal.com/
  http://www.sleevetown.com/
  http://www.american-digital.com/prodsite/category.asp?c=36

A warning about some double-disc jewel cases sold by CompUSA can be found
at http://www.yoyo-tricks.com/CompUSA-WARNING.html (along with pictures).
Apparently the pressure exerted on the hub causes cracks to appear over
time.  If a disc with a cracked hub is put into a high-speed drive, it
may shatter (see section (7-25)).


Subject: [7-11] What's "unbranded" CD-R media?
(1999/03/07)

Simply put, it's a CD-R disc with nothing printed on the top surface.  Some
people need "plain" discs that they can print on, or simply like them for
the aesthetic value.  There is no difference in quality or capacity.


Subject: [7-12] How do I repair a scratched CD?
(2002/06/15)

If you scratched the top (label) side of a CD-R, and it no longer works,
your disc is toast.  (If you scratched it, and it still works, copy the
data off while you still can.)

If you scratched the bottom side, then all you've done is etch the
polycarbonate (plastic), and it can be repaired like any other CD.  A common
misconception is that the data is on the bottom, but if you examine
it carefully you will see that the data is beneath the label.  The
laser reads the data through the polycarbonate layer, and if the layer
is scratched the laser will refract onto the wrong part of the disc.

For small or radial scratches, the error correction in the CD format will
allow the disc to continue working, but if there's too much disruption
you will get audible glitches or CD-ROM driver errors.

If the disc works some of the time, you can "repair" it by copying it onto
a new CD-R disc.  If the disc is always unreadable, or is copy protected,
you will need to repair the disc itself.

One product that may be useful is Wipe Out! (http://www.cdrepair.com/), a
chemical abrasive that allows you to reduce scratches.  Another is
Discwasher from http://www.discwasher.com/.

The Repair FAQ at http://www.repairfaq.org/ has a section on repairing
scratched CDs.  Find the "Compact Disc Players and CDROM Drives"
section, and skip down to 4.10 and 4.11.

Some people have suggested using plastic polishes or "fine cut" paint
polishes sold for removing fine scratches on automobiles.  These fill in
the scratches and create a more optically consistent surface.  Fine metal
polishes may also work, and some people claim that plain old white
toothpaste does the trick.  There is some chance that the filler material
will fall out over time, rendering the disc unreadable once again, and
possibly gunking up your CD-ROM drive along the way.  If you want to fill
in the scratches, you should make a copy of the contents to a new disc as
soon as possible, and stop using the original.


Subject: [7-13] What's this about a Canadian CD-R tax?
(2006/02/27)

In the United States, a distinction is made between "consumer digital
audio" media and data media.  You have to pay extra for consumer audio CD-R
blanks and DAT tapes, and the music recording industry gets a piece on the
assumption that the media will be used to hold commercially recorded
material.

Canada has gone a step farther, by placing a levy upon *all* media capable
of storing audio.  Even the "data" CD-R blanks, which don't work in consumer
audio CD-recordable decks, are subject to the levy.  Starting Jan 1 2001,
the levy was raised from CDN$0.052 to CDN$0.21 (a 4x increase) for CD-R
and CD-RW discs.

Some web sites with more information:

  http://neil.eton.ca/copylevy.shtml
  http://pcbuyersguide.com/hardware/storage/cdr-levy.html

See also http://www.cb-cda.gc.ca/news-e.html for a 1999/12/17 announcement
that the Levy has gone into effect, and http://www.cb-cda.gc.ca/news-e.html
for an announcement about the 2001 price increase.

http://www.cb-cda.gc.ca/tariffs/proposed/c25022006-b.pdf has the 2007
proposal, which continues the CDN$0.21 per disc price.  The price for discs
purchased in bulk quantities can more than double because of the levy.


Subject: [7-14] Can I get 80mm (3-inch "cd single") CD-Rs?
(2001/11/27)

The 80mm CD didn't catch on everywhere.  In some markets, notably the USA,
pressed "CD single" discs are rarely seen.  The 80mm CD-R made a brief
appearance, and then vanished for a while.  As of the middle of the year
2000, they were once again easy to find.  In mid-2001, Sony started
using them in one of their Mavica camera models, and towards the end of
2001 80mm-based MP3 players appeared.  They're pretty easy to find now.

Using them is not as straightforward as could be hoped.  Most *software*
will work just fine, because all CD-Rs have slightly different capacities,
especially when you consider 63-minute, 74-minute, and 80-minute blanks.
The problems stem from their physical dimensions.

Pretty much all tray-based recorders have grooves for 120mm discs and
80mm discs.  However, not all of them can actually record 80mm discs.
Web sites for recent drives will sometimes indicate whether or not they're
compatible.  Some CD recorders can read the discs but not write them,
possibly because the clamping mechanism raises the disc to a level where
it's no longer sufficiently supported at the edges.

If you have a caddy-based recorder, you will have a problem: while trays
have two different rings for 80mm and 120mm discs, caddies don't.
According to the Yamaha CDR-102 manual, there is a "Disk Adaptor",
referenced as part #ADP08, that sits in the caddy and keeps the disc
properly positioned.  A device that performed a similar function used to be
sold by music stores so that standard players could handle 80mm
CD-singles; it looks like a plastic doughnut that clips onto the disc.

If you have one of these, great.  If you don't, you may have difficulty
finding them.  You will likely have even worse luck figuring out how to
play an 80mm disc on a "slot in" CD-ROM drive -- the kind where you push
the disc into a slot, and it slurps it up.  Some manufacturers have
indicated that their traction-feed drives work fine with 80mm discs, but
before you try it might be wise to have a screwdriver handy.

A less common issue with 80mm discs has to do with playback.  A loose sheet
included with the CDR-100/102 "CD Expert" manual states:

  "An 8-cm disc recorded at normal speed on the CD Expert may not playback
  correctly on some manufacturer's CD-ROM drives.  This is likely on drives
  that have a playback PLL (phase lock loop) bandwidth of 1.5 kHz.  Most
  drives, however, have a playback PLL bandwidth of 2.5 kHz, in which case
  this is not a problem."

The final discouragement for 80mm discs is that they only hold 21 minutes
of audio (about 95250 sectors on Ritek silver-blue discs, or about 186MB),
but at present cost more than their full-sized counterparts.  They are an
interesting curiosity, and a cute gift when placed in a miniature jewel
case, but little more.  There appear to be 80mm discs that hold 34 minutes
(just shy of 300MB), but these come with the same caveats as 90-minute
120mm discs: the discs have to be constructed at or outside the limits of
what the specifications allow, and you may have problems with compatibility.

[ On a personal note: my Plextor 8/20 refuses to accept 80mm discs when I
put them in the tray.  I was able to use them with a (caddy-load) Yamaha
CDR-102 when I put the discs in a CD-single caddy adapter.  It turns out
that the Plextor 8/20 will write to the discs when the caddy adapter is
used for it as well.  There seems to be some problem with the Plextor's
mechanics when the disc is resting in the 80mm tray.  I don't know of a
source for the adapters, though I'm told http://www.cddigitalcard.com/
carries them. ]


Subject: [7-15] Where can I find CD-ROM business cards and "shaped" CDs?
(2005/11/08)

You can find CD-ROMs in many interesting shapes, including ovals and
rectangles.  These are functional CD-ROMs that are, for example, the same
size and shape as a traditional business card (well, a really thick
business card).  They can have your name and contact information printed on
the front, and can hold a modest amount of data, typically about 40MB.

Recordable CD-R business cards are available as well.

As with 80mm CDs (see section (7-14)), you may have trouble playing these
"discs" on CD-ROM drives that use caddies or have a "slot-in" design.

Some net.vendors (there are many others, but this is a good start):

  http://www.cdrom2go.com/
  http://www.newcyberian.com/
  http://www.cdshapes.com/
  http://www.pocketcd.com/
  http://www.cddigitalcard.com/
  http://www.sculptedcd.com/
  http://www.avomedia.com/record/index.html
  http://www.nycd.com/
  http://www.cdroutlet.com/
  http://www.xdr2.com/
  http://www.shimad.com/
  http://www.home-run.com/
  http://www.cdcardusa.com/
  http://www.americal.com/

For information about a 57.5mm disc with 80mm "wings", see
http://microdiscs.de/.

Cutting a CD-R disc into a different shape isn't recommended, because the
recording layer tends to delaminate easily once the seal has been broken.
Some CD-Rs have appeared in Japan that use a 120mm polycarbonate disc with
an 80mm recordable area.  This allows the outer polycarbonate to be cut
into interesting shapes without affecting the recordable area.  Some
pictures are available on http://www.fadden.com/cdrpics/.


What follows are some personal notes on CD-recordable business cards, based
on experiments conducted in early 2000.  I bought five from www.cdroutlet.com
for about $3 each.  According to CD-R Media Code Identifier, the essential
facts are:

	Nominal Capacity: 51.219MB (05m 51s 49f / LBA: 26224)
	ATIP: 97m 1As 55f
	Disc Manufacturer: Lead Data Inc.
	Dye: Pthalocyanine (Type 5)

The discs are gold in color, and look like an 80mm disc that was squared
off across the top and bottom.  They come in clear plastic envelopes that
are slightly larger than the discs themselves.  Total size is 80mm long
and 60mm wide, which is a little off from the standard business card
(88mm x 51mm) but not by much.

As with 80mm CD-Rs, my Plextor 8/20 rejected them unless I put them in an
80mm caddy adapter.  The adapter doesn't work very well, since it's only
holding the disc on two points, but it worked well enough.

I grabbed a local copy of my web page, threw on an autorun.inf and a copy
of shellout.exe, and wrote it to the disc with disc-at-once recording.
The recorder got upset while writing the leadout, and ECDC (3.5c) reported
some fatal errors, but the disc had already been closed enough to be
readable in the two CD-ROM drives tried.  It's possible that the slight
looseness in the caddy adapter caused problems... on future attempts I
will try to fasten the disc a little more securely.

The use of these discs as business cards presents some difficulties.
If you look at the picture on http://www.fadden.com/cdrpics/, you can see
that the disc has the same clear hub as a standard disc, which doesn't give
you much of a solid background for writing.  All is not lost, however: there
are other cards with ink-jet printable surfaces, and adhesive business
card labels are now available.


Subject: [7-16] Can you tell pressed CDs and silver CD-Rs apart?
(2004/03/03)

The easiest way is to drag something sharp across the top, perhaps some
car keys, and watch what happens.  If the top surface flakes off easily
and seems to want to peel up, it's a CD recordable.  If you'd like to be
able to use the disc afterward, there are some non-destructive ways too.

In some cases it's easy to tell, e.g. the color is slightly off or there are
two different shades of silver.  The written areas on a CD-R look slightly
different from unwritten areas.  A silver CD-R that has been written to
capacity is nearly indistinguishable from a pressed disc though, and some
pressed discs have distinctly visible regions.

You can get a definitive answer with CD-R Media Code Identifier (6-2-9).
Put the disc into a CD recorder and query it.  Pressed discs will say
"no information".  Some CD recorders might have trouble finding the ATIP
after the disc has been closed, so do some tests with known discs before
jumping to any conclusions.


Subject: [7-17] What's the difference between "data" and "music" blanks?
(2003/01/13)

"Consumer" stand-alone audio CD recorders require special blanks.
See section (5-12) for details.  There is no difference in quality or
composition between "data" blanks and "music" blanks, except for a flag that
indicates which one it is.  It's likely that "music" blanks are optimized
for recording at 1x, since anything you record "live" is by definition
recorded at 1x (though some dual-drive systems allow track copying at
higher speeds).

You don't have to use "music" blanks to record music on a computer or on
a "professional" stand-alone audio CD recorder.  Nothing will prevent
you from doing so, but there's no advantage to it.

The "music" blanks are more expensive than the "data" blanks because a
portion of the price goes to the music industry.  The specifics vary from
country to country.  In the USA, the money goes to the RIAA, which
distributes it to artists who have navigated through a complicated
application process.

Some manufacturers have on occasion marked low-quality data discs as being
"for music", on the assumption that small errors will go unnoticed.  Make
sure that, if you need the special blanks, you're getting the right thing.

(Technically, there are actually three kinds of blanks: type 1a for CD-ROM
or professional audio recording, type 1b for special-purpose applications
like PhotoCD, and type 2 for unrestricted use.  "Music" blanks are type 2,
"data" blanks are type 1a.)

Some disc manufacturers label "music" blanks as "universal use", since
they will work on anything.


Subject: [7-18] How do I convert data CD-Rs into "consumer audio" blanks?
(2002/02/25)

The CD-Rs required by "consumer" stand-alone audio recorders (section
(5-12)) are more expensive than the standard "data" CD-Rs.  Converting a
standard blank into a consumer-audio blank is like converting lead to gold,
in two ways: it would save a lot of money, and it's impossible.

CD-Rs have some information pressed into them that cannot be altered.  One
such tidbit is the Disc Application Flag, which tells the recorder what
sort of blank you've inserted.

There are ways to trick certain recorders into accepting other kinds of
blanks (some of which are mentioned in section (5-12)), but there is no
way to disguise the blank itself.

(For the nit-pickers: apparently some experiments with nuclear reactors and
particle accelerators have actually resulted in conversion of lead to gold.
It is unlikely that placing a "data" CD-R in a particle accelerator will
do anything useful, however.)


Subject: [7-19] Is translucent media bad?
(2002/12/09)

A popular perception is that translucent CD-R media -- discs that are,
to some extent, see-through -- are lower in quality than discs you can't
see through.  The argument is that the discs reflect less light, and as
a result are less likely to work in some players.

The argument is without merit.  So long as the disc reflects at least 70%
of the beam when it strikes a "land", it meets the CD-R specification.

All CD-R media, except for discs treated with an opaque top coating
(usually to provide an absorbent surface for ink-jet printers), are to some
extent translucent.  Take your favorite brand of un-coated disc, write
on the top with a black marker, and hold it up to a bright light source.
The writing will be visible through the disc, even on widely recommended
high-end brands.

Suppose the translucent media had an opaque label added to the top.  Now
that you can't see through it, is the quality of the media higher?

There is much more to media quality than its ability to reflect the visible
light spectrum.  It can be argued, of course, that there is a correlation
between the process that yields discs that are easy to see through and
discs that don't work very well.  There is, as yet, no proof that such a
correlation exists.


Subject: [7-20] How do I destroy CD-R media beyond all hope of recovery?
(2005/08/11)

This question comes up every once in a while, because somebody with sensitive
data wants to obliterate unwanted copies on CD-R.  With magnetic media,
the problem is well understood, and guidelines have been published for
the proper treatment of floppy disks and hard drives.  To the best of my
knowledge, no such guidelines have been published for CD recordable media.

To be effective and useful, an approach must have two properties: it must
guarantee that there is no hope of recovering any data from the media, and
it must be safe and easy to implement.  The qualifications for the former
involve a fair degree of paranoia.  If, for example, you want to erase a
file from a hard drive while leaving the remaining contents intact, it is
necessary to write over every sector in which the file was written several
times with different bit patterns.  If you just zeroed out the blocks,
a sufficiently sensitive device could detect lingering magnetic traces,
and possibly reconstruct significant pieces of the original file.

Some possible approaches for CD-R:

  Death by physical delamination
    Scrape off the reflective layer with something sharp.  Can be done by
    an unskilled worker or simple device.  You still need to do something
    with the reflective layer, though, and there might still be traces of
    data on the polycarbonate (dye residue).
  Death by shredding
    Run the disc through an industrial-strength paper shredder.  The
    polycarbonate tends to shatter into many small pieces.  The resulting
    jigsaw puzzle should be exceptionally difficult to reassemble.
    The trouble is that the reflective layer and underlying dye is very
    flexible once separated from the polycarbonate, and might not shred
    well.  (A much simpler variant of this is to snap the disc in half.
    If you do it the right direction, the polycarbonate breaks into
    several pieces.  You may want to tuck the disc inside a magazine or
    newspaper to control the shrapnel.)  Many "home office" shredders
    will handle CDs now.
  Death by drum sander
    Secure the disc to a piece of wood, and run it through an industrial
    drum sander (http://www.performaxproducts.com/Catalog/SuperMax50x2.html).
    These come with dust vacuum hoods, which should minimize the amount
    of breathable polycarbonate.  The system would have to be calibrated
    carefully though, or the sander might just rip the data layer off and
    fling it (or, for that matter, fire the whole disc across the room).
    Using the piece of wood more than once might be problematic, depending
    on the exact method used to attach discs to it.
  Death by chemical delamination
    Drop the disc into acetone.  That ought to dissolve the top layer
    and leave little left that's meaningful.  Something still needs to be
    done with the polycarbonate, though, in case it retains any traces of
    the data, and disposal of acetone can be a problem.
  Death by incineration
    Pop the disc into a wood-burning stove.  Quick, easy, effective, and
    really bad for the environment.  The fumes from burning polycarbonate
    are not recommended as a treatment for lung disorders.  Elevating a CD-R
    disc above 250C (about 480F) should cause it to become fully "recorded",
    but it's possible that some traces of the original recording would
    remain.
  Death by microwave
    Microwaving a disc for a few seconds renders it pretty well unusable.
    It's not clear how thorough this process is.  A visual inspection
    suggests that some regions of the disc go relatively untouched.
  Death by coherent light
    The disc was written by a laser that turned on and off.  Presumably
    it is possible to modify a CD recorder such that it turns the laser
    on and leaves it on.  This would obliterate all of the data on the
    disc.  It's not clear if a sensitive detector could see regions that
    were "written" twice.
  Death by sandblasting
    Blasting discs with sand will certainly take the reflective layer
    off, and do a pretty fair job of scrubbing them clean.  The only
    concern is for whether the delaminated layer gets fully pulverized
    or just sheared off (and stays intact).
  Death by sidewalk
    This approach is similar to the others, but can be performed with
    inexpensive equipment: a patch of rough cement and a rubber-soled
    shoe.  Put the disc, shiny side up, on the sidewalk.  Step on it,
    and twist vigorously while applying pressure.  This will gouge the foil
    and polycarbonate, and with sufficient force may even split the disc
    itself.  More force may be required on disks with adhesive labels,
    and cleanup can be tricky on a windy day.

There doesn't seem to be a simple answer or perfect method.  If you aren't
concerned about the NSA or a major national power recovering your data,
though, scratching with car keys or snapping in half with your hands should
be all the security you need.


Subject: [7-21] Can I recycle old CDs, CD-Rs, and CD-RWs?
(2004/08/31)

Yes.  One such recycling company, Polymer Reprocessors (in the UK), has
a nice web page describing what happens to the materials.  Visit
http://www.polymer-reprocessors.co.uk/.

Others:
 - GreenDisk, http://www.greendisk.com/
 - Plastics Recyling Incorporated (no web site) -- Indianapolis, IN USA
   317-780-6100.


Subject: [7-22] Is there really a fungus that eats CDs?
(2005/10/12)

Yes.  It appears to be limited to tropical climates.  Two articles from
mid-2001 (no longer on original sites, so archive.org links are provided):

 - http://web.archive.org/web/20041101034932/www.ananova.com/news/story/sm_328113.html
 - http://web.archive.org/web/20040608203933/http://www.nature.com/nsu/010628/010628-11.html

The incident in question was discovered by a researcher from Spain who
visited Belize in Central America.  What is believed to be a strain of
Geotrichum entered a CD from the outer edge and destroyed the aluminum
reflective layer as well as some of the polycarbonate.

A person in Australia reported a few years earlier that store-bought pressed
CDs were getting eaten, but gold CD-Rs were doing rather well.


Subject: [7-23] How do I clean CD-R and CD-RW discs?
(2004/02/22)

The short answer is, clean them the same way you would a pressed CD.  Take a
lint-free cotton cloth and wipe from the center out.  It's important to
move in a straight line from the hub to the outside, rather than moving in
a circular motion.  The act of cleaning could cause the surface to abrade,
and the error correction employed is better at correcting scratches and
marks that go from the center out.

You have to be a little more careful with CD-Rs than you are with pressed
CDs, because the lacquer coating may not resist certain chemicals as well.
Some CD-R discs all but fall apart when exposed to alcohol.  Some really
cheap ones start to dissolve in tap water.  Your best bet is to just use
a dry, clean, soft, lint-free cloth, like you would use to clean the lens
of a camera.

(In practice, a wadded up tissue works pretty well, but it's best to avoid
paper products.  Lens cleaning papers are great for glass, but polycarbonate
is much easier to scratch.)


Subject: [7-24] Are "black" discs different from other discs?
(2003/08/24)

Yes and no.  Your eyes can tell you that the disc is different, but the
laser in the CD player can't.

A "black" disc, popularized by the tint added to Playstation games, has
had color added to the polycarbonate layer.  The tint looks very dark to
the eye, but so long as it doesn't absorb or disperse too much light in
the laser wavelength it won't interfere with disc performance.  If you
hold the disc in front of a light, you may discover that your "black"
disc is actually very dark red.

Some people have suggested that, by blocking other light, the coloration
enhances the performance of the disc.  This makes about as much sense
as drawing around the outside of the disc with a green magic marker (a
popular myth from the 1980s).

If you find that "black" discs work poorly or especially well, you haven't
discovered anything different from what most owners of CD recorders know:
some discs just work better than others.  The tint in the plastic isn't
likely to be involved.

(Some users have done some fairly careful testing, and found that "black"
audio discs sounded better than non-black discs from the same manufacturer.
I haven't seen a controlled double-blind study that reached this conclusion,
but there is anecdotal evidence to suggest that the colored polycarbonate
causes the discs to sound different.)


Subject: [7-25] My disc just shattered in the CD drive!
(2004/03/03)

This is rare but not unheard-of.  Spinning an object at high speed puts
it under a lot of strain.  Poorly-balanced discs can cause vibrations and
make the problem worse.

Drives rated at 52x typically spin somewhere between 10,000 and 12,000 RPM
(see section (5-22) to see how this is calculated).  This is not enough to
shatter a disc in good condition, but more than enough to destroy a disc
with minor defects.  This is one reason why Sony's 52x drives default to 40x
maximum, with a "turbo boost" feature that enables 52x reading and writing.

Super-fast drives, e.g. 72x, are actually spinning more slowly, but employ
multiple read lasers to read from more than one area of the disc at a time.

http://www.rm.com/safety/ has some warnings and safety advice.  There is
a PDF document http://www.rm.com/safety/Downloads/StructuralIntegrity.pdf
containing a thorough analysis of the problem.  The study concluded that
uncracked discs are not expected to shatter in 40x and 52x drives, but
discs with small cracks near the hub of the disc are at risk.

If you have a disc with a visible crack in it, DO NOT use it in your
CD-ROM drive unless you can reduce the speed to 8x or below (the slower
the better).  Not all drives can be slowed.  For Plextor models use the
tools that came with the drive; for some models there are speed-reduction
applications available on the web; for others you're simply out of luck.
Nero DriveSpeed (http://www.cdspeed2000.com/go.php3?link=nerodrivespeed.html)
will work for many drives.

Some web pages with destructive experiments:
 - http://www.powerlabs.org/cdexplode.htm
 - http://www.qedata.se/e_js_n-cdrom.htm

An episode of the Discovery Channel's "Mythbusters" TV show demonstrated
discs flying apart near 30,000 RPM.  This speed would only be necessary for
a 150x drive.  Apparently they assumed that 52x drives read at 52x across
the entire disc, rather than just at the outside where the amount of data
read per revolution is higher.


Subject: [7-26] How do I tell which side on a silver/silver disc is up?
(2002/02/25)

There is one approach guaranteed to work: put the disc in the drive.  If
it works, you have it right.  If it doesn't, eject it and turn it over.

Alternate approach: many discs have numbers or letters printed near the
hub.  If they appear to be written backwards, the disc is upside-down.

Another approach: hold the disc edge-on in front of you, so you're looking
right across the surface of the disc.  Tilt it up slightly, and look
closely at the edge farthest from you.  When it's the right way up you'll
just see the label, when it's the wrong way up you'll be able to see
some light through the polycarbonate.

Yet another approach: the area of the disc near the hub may feel different
(one side may have a groove or a lump that the other doesn't).  Figure out
which side is which, then remember how the disc feels.


Subject: [7-27] How should I handle and store CDs?
(2004/02/20)

This list comes substantially from NIST Special Publication 500-252,
available from http://www.itl.nist.gov/div895/carefordisc/.  Most of it
is common sense.

 - Handle discs by the outer edge or the center hole.  Don't touch the
   surface of the disc, or you'll leave fingerprints and oil behind.
 - Label the disc with a non-solvent-based felt-tip permanent marker.
   Beware of permanent markers that contain strong solvents.  The use of
   adhesive labels is not recommended for long-term storage (more than
   five years).  If you do use a label, never try to remove or reposition it.
 - Keep the disc free of dirt and other gunk.
 - Store discs vertically rather than flat.  Over a long period, gravity
   will warp the disc if it's left flat in a jewel case.  Most jewel
   cases support the disc by its center, holding it off the backing.
 - Return discs to storage cases immediately after use.
 - Open a recordable disc package only when you are ready to record
   data onto that disc.  If your discs came on a spindle, leave them on
   the spindle until you need them.
 - Store discs in a cool, dry, dark environment in which the air is
   clean.  Avoid areas that are excessively hot or damp.  Keep them away
   from direct sunlight and other UV light sources.
 - Clean dirt, smudges, and liquids from discs by wiping with a clean
   cotton fabric in a straight line from the center of the disc toward
   the outer edge.  Never wipe in circles.  The error correction codes
   on the disc can handle small interruptions, such as a scratch that
   travels across the spiral, but can't handle large interruptions, such
   as a scratch that's traveling in the same direction as the spiral.
   Avoid paper products, such as lens-cleaning paper.
 - Clean stubborn dirt and foreign substances with 99% isopropyl alcohol
   or 99% methyl alcohol (methanol).  Apply the cleaner to the cloth,
   then rub the cloth across the disc, taking care not to get any fluid
   on the label side of the disc.  Some labels or coatings may not react
   well with alcohol.
 - Do not bend the disc.  Flexing the disc can cause stress patterns to
   form in the polycarbonate, and if you stretch it far enough you might
   start to deform the reflective and recording layers.  Take care when
   pulling discs out of tight jewel cases.
 - Do not expose the disc to rapid changes in temperature or humidity.
 - Use quality discs from an experienced manufacturer.  Low-quality
   discs will degrade quickly, even under ideal conditions.

A temperature between 20C (68F) and 4C (39F) with a relative humidity of
20-50% is recommended.  Before you go stuffing all of your discs in the
refrigerator, make note of the fact that rapid changes in temperature and
humidity can be harmful.  You would need to let your discs slowly come up
to room temperature before placing them in a CD player.  Discs that are
accessed frequently should be stored in an environment similar to the one
in which they will be played.


Subject: [7-28] What causes the rainbow effect when looking at the data side?
(2004/03/03)

A CD has a single spiral track, each revolution of which is separated by 1.6
microns on a 74-minute disc (less on higher-capacity discs).  The mirrored
"grooves" act as a reflection diffraction grating, causing interference
patterns in the reflected light.

Some related web sites:

 - http://science.howstuffworks.com/question52.htm
 - http://www.u.arizona.edu/~tagin/Report.html


Subject: [7-29] Can I print directly on a CD-R?
(2005/11/08)

Yes, with the right setup.  You have to use media with a printable surface
that holds ink, and you need a disc printer.  One equipment source is
Primera Technology (http://www.primera.com/).

It's also possible to use offset printing (the process used to print
newspapers and magazines).  Some additional information can be found at
http://www.newcyberian.com/.