Copper Print

Below are the "original formulas" published 1978 in Popular Photography's "How to Guide". Though consultation Cor Breukel has been working on improving the process.

SAFETY NOTE: always wear gloves and safety glasses. I also recommend a lab coat or other outer garmet, long pants and closed toed shoes.

There are two related formulas. Use the one you can get the materials for. The resulting mix is the same.

FORMULA 1, to 20ml of water add:

4.8 grams sodium hydroxide
3.7 grams citric acid
3.7 grams acetic acid (glacial, 100%)
2.5 grams copper sulfate
 
let cool, then add:
   
2.0 grams potassium ferricyanide
0.5 grams potassium persulfate

NOTE: add in order listed.
adding an acid directly to potassium ferricyanide
could result in your DEATH!

A safer way to mix this formula is:

FORMULA 2, to 20ml of water add:

5.0 grams sodium citrate
5.0 grams sodium acetate
2.5 grams copper sulfate
 
let cool, then add:
   
2.0 grams potassium ferricyanide
0.5 grams potassium persulfate

You will need to coat starch sized paper twice or agar sized paper once.

Start with a 6 minutes exposure in direct sun in a contact printing frame.
Your negative need to be a little stronger than for a silver print.

To fix, gently wash in water for five minutes.

To intensify:

to 250 ml of water add:

5 grams of acetic or citric acid
0.1-0.5 grams of Amidol (2,4 diaminophenol dihydrochloride)

Will not keep and needs to be made up fresh. Immerse the copper print in above until the color stops changing (fast reaction), then wash and dry. The print will get noticably more intense upon drying, especially if you do the final drying under a household iron or in a dry mount press.

The formulas will work on cotton frabric as well. I don't know how well it will hold up to washing. As copper salts can be mildly toxic, I would not recommend for clothing or food preparation.

STRANGE ADAPTION

This is the formula for a direct postive copper print.
Noticably less sharp but whiter whites.

to 25 ml of water add:

5 grams of sodium citrate
5 grams of sodium acetate
2.5 grams of copper sulfate
2.0 grams of potassium dichromate (nasty carcinogen!)

expose paper from 5-20 minutes and develop in 1% sodium ferrocyanide [NOT ferricyanide!]
then wash for a few minutes in water.