First, do you really want to? You can make rough breakup gobos fairly
easily, but standard stock breakups are only a few dollars. If you have
specific artwork you want to make into a gobo then you'll need to make
it by etching.

You have three options, of which only the first two can be recommended!
   1 Get it professionally etched. Your local lighting supply company
     should be able to point the way to a company offering this service.
     ROSCO make custom gobos, but their pricing and delivery time may
     not be competitive with someone closer to you.
   2 M&M make an etching kit in a briefcase called the M&M gobomaker.
     This is available for hire from a number of rental companies
     worldwide, or if you think you'll be making lots of custom gobos
     you could buy a kit.
     Contact www.mandm.co.uk (website); info@mandm.co.uk (email);
     +44-171-284-2503 (phone); or +44-171-284-2503 (fax)
   3 If you really like spending time and money and playing with
     dangerous chemicals, follow the instructions below.

For abstract break-ups or very rough gobos any thin sheet metal will
work. Scrap printing plates from a newspaper printers work OK. I've even
seen gobos made out of flattened coke cans (tho' the thin aluminium
softens). Cutting a pattern is easy if you have access to a pillar
drill. The thin aluminum used for litho plates can be cut with sharp
craft knife.

For photo-etched gobos:
   1 You need high contrast original artwork, with completely opaque
     black areas.
        * Computer graphics laser-printed onto transparencies works
          well, artwork photocopied onto transparencies is OK
        * The black areas must be completely opaque. Any holes or grey
          areas can be filled in with a black spirit marker
        * A product called 'Lasercolor' will bond to toner, making the
          image more opaque
        * Scotchcal 8007 reversal film, usually used for making
          photoetched PCBs makes great artwork
        * Surround the image with an opaque shape leaving the outline of
          the gobo - that way the gobo will fall out of the blank when
          etched
   2 Choose and prepare the gobo material
        * Brass, copper and aluminium are the possible choices.
             * Stephen Lane recommends 0.2mm brass shim, available from
               model shops or a non-ferrous metals dealer.
             * Aluminium is cheaply available from scrap litho printing
               plates from a local newspaper, or from a flattened drink
               can. I've seen aluminium gobos soften within a few
               seconds in 1kW lanterns
        * Cut a blank an inch or two larger than the gobo you're making
        * Clean the surface thoroughly, getting rid of any grease and
          removing the oxide coating.
   3 Photoresist
        * Coat one side of the blank with a positive photoresist (such
          as Electrolube PRP200).
        * Coat the other side with a protective laquer (such as
          Electrolube CPL200)
   4 Fix the artwork to the blank
        * Put the side of the artwork with the toner on it touching the
          blank (this improves fine detail)
   5 Exposure
        * The blank needs to be exposed to 'enough' UV light to expose
          the resist in the uncovered areas, but not enough to expose
          the remainder
        * The best way to expose it is to use a hobbyist PCB exposure
          box. If you intend to do many gobos, or intend to make any
          PCBs it's worth looking at one of these
        * Fluorescent UV tubes are the next best option, with the
          artwork fixed to the blank with four bulldog clips. This takes
          50-90 seconds at a range of two inches
        * Mercury vapour worklights and sunlight can be used, but aren't
          recommended. The worklights produce a lot of heat, which can
          damage the resist, and sunlight is a bit unpredictable.
   6 Next develop the resist, using the relevant developer (eg
     Electrolube PRD200)
   7 Any holes in the resist can be touched up with a spirit marker or a
     'resist touch-up pen' from the same supplier as the rest of the PCB
     stuff.
   8 Etching
        * For brass or copper the best etch is ferric chloride. Ammonium
          persulphate works too, but you have to be careful of fumes
          given off, and heat produced can make the resist flake off.
        * For aluminium one part hydrogen peroxide, one part
          hydrochloric acid (what strength? -- SRA) to four parts of
          water works well. This is a very corrosive mix. If you don't
          know about safe acid handling precautions don't do it. Use
          acid-proof gloves, apron and eye protection. Use glass, or
          maybe plastic containers. Don't store unused etch, dilute it a
          lot and dispose of it safely. Another reason not to use
          aluminium for etched gobos.
        * Keep an eye on it as it etches. If anything starts to etch
          that shouldn't you can take it out of the etch, flush it with
          water, touch up the resist with a spirit marker and drop it
          back in the etch.
        * Serious electronics hobbyists use small 'bubble etch' tanks.
          These heat the etchant and blow bubbles through it. This gives
          a faster and more uniform etch
   9 Acetone, or whatever solvent the resist manufacturer recommends,
     will strip off the resist and laquer

Loosely adapted from posts by Stephen Lane of Apollo Lighting, with
extra bits from David Gibson, Clive Mitchell and Steve Atkins.

Practice a couple of times on some scrap to get the exposure time
correct. The first time I use an exposure box I coat a piece of scrap
with resist. Then I cover most of it with a piece of foil and expose for
15 seconds. Then I move the foil down a half-inch and expose for another
15 seconds, and so on. Then when I develop and etch this test piece I
can see how each exposure time works -- SRA

The whole process of making brass gobos is very similar to making PCBs,
so hobbyist electronics books may be useful for more info and pictures
(Stephen Lane intends to make photos available on the web sometime
soon). The PCB FAQ, posted to sci.electronics or available at
http://www.ecn.uoknor.edu/~jspatric/faqs/pcb.faq is well worth a look.

Variations to this are the toner-transfer and direct methods

Direct etching is pretty simple. Rather than use photo-resist you simply
draw your pattern onto the blank with an etch-resist pen, or coat the
blank with laquer and scribe your design into it. Then you etch the
blank as described above.

The toner transfer method is popular for making simple low-tech PCBs.
I've never heard of anyone trying to make gobos with it, and the longer
etching time needed for gobos might make it difficult to get
toner-transfer to work well. Basically you photocopy the densest,
blackest artwork you can onto paper, or better, special toner-transfer
paper. Then you put the paper over the blank, toner touching the
(sandpapered clean) blank. Then you iron it with a hot iron, fusing the
plastic component of the toner onto the metal. The you soak it in water
to lift off the paper.

Toner-transfer instructions can be found at
http://clarc.phoenix.net/laserpcb.html

If anyone trys toner-transfer for gobos, please email me to tell me how
well it works.

In the UK all of the equipment and chemicals are available from Maplin
Electronics ( http://www.maplin.co.uk/ , full address elsewhere in the
FAQ).

The chemicals are available from Electrolube Ltd., Blakes Road,
Wargrave, Berkshire, RG10 8AW, +44 1734 404031.

Check the ads in any electronics magazine for local suppliers