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→Overview of the Process
The mixture of water, gelatin, and dichromate, still warm, is applied to glass plates. The simplest method is called veil coating in which the mixture is poured onto an angled plate and allowed to flow over it. Other methods include first pouring a line of mixture at one end of a plate then using a Meyer bar or doctor's blade to drag the mixture across the plate. Spin coating is possible, but at much lower rotational speeds then is used for, say, integrated circuit production, and tends to be very wasteful of mixture. Low-speed spinning can be used after any of the other coating methods to get a more even distribution.
Coated plates are then allowed to dry. The They are usually ready for exposure 4 to 12 hours later. Since dichromated gelatin can be 1,000 times less sensitive to light at 532 nm (for example) than silver halide emulsions, exposures may take a while.
After exposure, the plate is left to sit in the dark for a few minutes before processing begins. Fixing is first, and this can be done either chemically with a standard photographic fixer or optically with a few seconds exposure under intense white light. Washing is next to remove the dichromate from the gelatin. Finally comes the drying step, and this involves a sequence of progressively more concentrated isopropyl alcohol baths, the last bath being 99% alcohol. Hot air drying is next to remove the alcohol.
