These bright red-orange crystals are invaluable to holographers, as they can be the oxidizers in both reversal and rehalogenating bleaches, as well as being a sensitizer for the holographic recording material known as Dichromated Gelatin, or DCG for short.
Here is what the Photo-Lab Index from Morgan & Morgan has to say about it:
This is one of the essential chemicals for the silver halide holographer, and those who practice the fine art of DCG. Its most common application for the former is in the compounding of the bleach that is used in the Pyrochrome processing scheme. here is the formula:
Pyrochrome Bleach
4 g Potassium Dichromate
4mL Sulfuric Acid (or 12 g Sodium Bisulfate)
One litre water
This bleach is a weaker version of the Kodak R-9 Bleach, whose original purpose was to bleach out developed silver in B&W movie film to process it into a positive, reversing the negative action of traditional materials, so these formulae are sometimes referred to reversal bleaches. But a more accurate chemistry descriptor would be silver solvent bleach, as this solution makes the developed silver metal dissolve in water.
Kodak R-9
9.5 g Potassium Dichromate
8 mL Sulfuric Acid (or 24 g Sodium Bisulfate)
One litre water
Originally the use of an acidified dichromate bath in photography was to clean trays in which silver precipitates accumulate on their bottoms. It is an even stronger solution than the above, like in this Tray Cleaner.
Although the blurb from the Photo-Lab Index from Morgan & Morgan above mentions that potassium dichromate is non-corrosive to metals, the bleaches above will etch holes in stainless tanks and trays over long periods of time. Plastic is a better choice.