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The pin image is repeated as many times as practical to fill up the entire photographic sheet. This sheet varies in size. The photographic sheets are made of metal and coated with a photo-active emulsion. The film negatives are exposed onto the sheet (front and back), which removes the emulsion from the area to be etched. Normally the back side of the sheet is covered with emulsion because there is no etching on the back.
The photographically exposed sheet is then placed in an etching bath where a chemical eats away the exposed metal. The depth of etching is controlled by the strength of the bath and the time of immersion. The etching solution eats into the the metal on the top surface creating cavities in the exact pattern created by the designer. The metal is etched completely through the outer shape because the solution attacks the metal from both sides. After being removed from the solution the individual pieces are popped out of the metal sheet. Occasionally, light trimming is required to remove any burrs. The individual pieces are cleaned and readied for fastener and finishing. After plating, the shallow cavities are usually filled with a soft enamel. The “tooling” for photo etching is relatively inexpensive and is capable of great detail.
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