Cyanotype toning in sodium sulfide and how to fix?

I just read a post from KORAKS in this forum on how to make a cyanotype turn black into iron oxide, and remembered an experiment I did two summers ago. I was experimenting with sodium sufide, my favorite toner for silver prints, and though what would that do to a cyanotype? Would we get ferric sulfide (mars black)? So I slipped an old cyanotype into a very dilute sodium sufide solution, and it immediately turned an gorgeous deep black color with better tonality than I've ever seen. I was very excited by this, so put a bunch in, then washed and dried. During washing, the tone was reducing a bit. After drying, the black tone had disappeared and turned into the yellow tone that we get from bleaching a cyanotype, and could be toned in tannic acid the same way as after normal bleaching. I think tinkered the next few days trying to find a way to fix that beautiful pure black toned image to no avail. I tried acids, bases, and even hypo, and nothing worked. The toned image was obviously not ferric sulfide, which is very stable substance. What was it? Can it be fixed? It was obviously oxidized.

Comments and suggestions very welcomed.

Tone another one, but this time don't wash it. Hang it up to dry and see if the black stays...

Thanks Andrew, I tried that before and it didn't work. I will try toning a bleached cyanotype next time around.

I have no real idea what the black compound you formed. Maybe Iron(III) sulfide? Which is not stable.

Other thoughts on iron sulfide chemistry...

Iron(III) sulfide (Fe2S3) is slightly soluble in water and a bit more soluble in acidic solutions.

Iron(II) sulfide (FeS) is insoluble in water but it will react with water in acidic solution to form H2S and hydroxide. You would easily recognize if this is happening from the "rotten egg" smell characteristic of H2S.

Sulfide is a strong base and thus will likely cause the bleaching of Prussian Blue (as do carbonate and ammonium hydroxide, which are commonly used to bleach cyanotypes before toning).

Sulfide is also a good reducing agent and thus will convert Iron(III) to Iron(II). This will also cause degradation of Prussian Blue.

My conclusion... sulfide is not likely to be a useful toner for cyanotypes. But... you have already demonstrated this!!!!

Eventually oxidizing to iron sulfate leaving your paper acidic and with a weak image. Your only hope would to mount it in a hermetically sealed oxygen free environment!

gealto2 said:

I just read a post from KORAKS in this forum on how to make a cyanotype turn black into iron oxide

Click to expand...

For the record (in case anyone hits upon this in a search): this was speculation on my behalf. I do not have a method to turn Prussian blue into black iron oxide.