A method of photographic printing that uses coper salts. The resulting prints are a rusty red or ochre color.
From an article on alternativephotography.com you can see some of Frank's cuprotypes at his website.
Ingredients:
Mix three solutions of Ferric Ammonium Citrate, Copper (II) Sulfate, and Sodium Thiosulphate.
50% (w/v – weight in volume) ferric ammonium citrate – Dissolve 50 g of ferric ammonium citrate in about 75 mL of distilled water. – Bring volume to 100 mL with distilled water. – Mix well and store in a brown bottle away from light.
10% (w/v – weight in volume) copper (II) sulfate – Dissolve 30 g of copper (II) sulfate pentahydrate in about 200 mL of distilled water. – Bring the volume to 300 mL with distilled water.
10% (w/v – weight in volume) sodium thiosulphate (‘hypo’) – Dissolve 20 g of sodium thiosulfate (“hypo”) in about 150 mL of distilled water. – Bring the volume to 200 mL with distilled water.
When ready to coat mix 1:3:2 (A:B:C)
2 % (w/v – weight in volume) potassium ferricyanide in water:
Working solution: Slowly add solution B to solution A with constant stirring. Then add 5 mL concentrated HCl.
I received this recipe from Peter after inquiring about his bright red cuprotypes.
Ingredients:
Use a tall beaker as mist is generated from the baking soda. Best done outside or good ventilation due to copper containing mist formation while making.
Stir very well and eventually the solution will turn a beautiful mid- deep blue. A small amount of sodium bicarbonate may sit on the bottom - that is ok. When using, draw off from the top. Store in bottle - not light sensitive and an unlimited shelf life.
Now you need to make up 25 ml of a potassium ferricyanide solution of 30% w/v.
In 21 ml of distilled water -warmed, not hot, add in 7.5 g potassium ferricyanide ( orange crystals) stir til dissolved. It will be of a deep yellow-orange. It may be a bit hazy. I usually filter it by tamping part of a cotton ball into a plastic funnel and pouring the solution in, or you could use filter paper. Preferably keep this solution in a brown bottle as it is a bit light sensitive- should last for a couple of months. If you place both solutions in their own dropper bottles, then it is convenient to do drop counts for small prints.
In a shot glass, I add In 10 drops each of the A and the B. You will see an emerald green when mixed. With a 1” brush, previously dampened, brush this in your watercolour paper- it will look a lime green. Leave to dry for 1/2 hr in the dark. Buffered papers are safe to use and have no known effect on how the print develops out but results will vary considerably with paper choice, just like all alt processes. You may need a more dense negative than with cyanotype as the cuprotype scale with this process is longer.
From this Photrio thread
10mg water, 1mg ferric ammonium citrate, 0.4g sodium thiosulfate, 0.6g copper ii sulfate, 1.2g 5% silver nitrate solution
Also a note that "increasing the amount of silver nitrate speeds up printing time. Going from 1.2 to 1.3g 5% silver nitrate"