In the US copper sulphate is very cheap, as it's used by florists for
something or other (called "blue vitriol!), I used to buy it for $7 a
pound from regular chemical houses.
Anyway, Peter has pretty well described the process.
But I found the folder & can add:
"Mordancage" is apparently the spelling, so Luis was right about that.
However I was wrong about the inventor, which has 2 r's in Marriage, so
it evens out.
And here are some references:
United States Patent Office, Jan. 10, 1950, patent # 2,494,068
"Photographic Relief Image."
Glafkides page 668 "Relief Images by local softening of the gelatin"
British Journal of Photography, April 211, 1944 "Notes on Etch-Bleach Baths"
Neblette Handbook, page 124
And see the chapter in Greeleaf on reversal processing, page 93, and page 96
My notes do not reveal which formula I used -- I had the bottles labeled
& they have long since been recycled.... but basically you can use acetic
acid or nitric acid, I may have used the acetic (easier to get & handle)
in a formula such as
EB-6 (my number)
3 grams copper chloride
5 cc glacial acetic
250 cc water
(at use) 50 cc of 3% hydrogen peroxide
EB-6A, above with 100 cc hydrogen peroxide...
When the gelatine is removed, you can not only reverse the image by
re-exposure & development, but dye the paper base.... or did Peter say
that already?
Judy