PDA

View Full Version : Toning Van Dyke brown prints with thiourea



koraks
15-Sep-2016, 14:33
I was wondering if anyone does this. I'm talking about toning Van Dyke brown prints with thiourea toner - not thiourea-gold, but regular thiourea toner as used for sepia toning silver gelatin prints.

A few weeks ago the thought came to me that it should be possible, although it didn't seem to make much sense to tone already brown prints with a sepia toner. Yet, some color shift seemed likely and possibly slightly better keeping properties of the print due to protection of the silver particles by binding them with sulphur. At least, that's what my tiny brain could come up with and I had no way (still don't) of verifying this from a theoretical viewpoint. Google turned up nothing - only references to thiourea-gold toners. I have no books on alt processes, so that didn't help either.

So I just tried it. I have two separate solutions to make up a sepia toner: a ca. 10% thiourea solution and a 10% NaOH solution. I first tried it with roughly equal amounts of both, diluted further to about 1+1+5. I tried toning before and after fixing. Before fixing resulted in severely fogged highlights; after fixing as well, but a little less badly so. The image tone shifted to a very dense, rather neutral and slightly metallic black in the shadows and an unattractive greenish tone in the mid tones and highlights, a bit like strong sepia toning taken too far. The dmax was appealing, image tone wasn't.

I then tried the opposite: acidifying the thiourea slightly by adding a small amount of 40% citric acid instead of the NaOH. This renders the toner virtually inactive. Didn't work too well either.

Then I decided on seeking out the middle ground. Roughly 1+0.3+5 of 10% thiourea+NaOH+water. Toning with this toner after fixing shifts the reddish town of the wet print to chocolate brown, with the yellow tint in the midtones and highlights shifting to more neutral brown as well. Upon drying the prints end up rather neutral, but a bit warm (brown with no apparent reddish tones). Dmax is good and there's no silvering / metallic sheen in the blacks. I quite like the results but have no clue about image permanence, having tried this only recently.

Edit: note that I skip the bleach step that is required with silver gelatin prints. Haven't tried it but my bet is that it will all but fade the print entirely, although theoretically it could work if absolutely no fixer remains in the paper and agitation and bleach time are kept to a minimum. A very dilute bleach also seems a good idea, but I'm not sure if there would be any benefit in adding a bleach step.

Has anyone else tried it? Does anyone do it regularly? What are your experiences? Can anyone comment on the chemistry that's going on?

koraks
3-Oct-2016, 00:46
So...nobody tried this? Does anyone have any thoughts to share, or even speculations? I'd love to hear about them!

Jim Noel
3-Oct-2016, 13:51
I occasionally tone my VDB prints, especially the nudes. When I do I always use thiourea gold toner, and never bleach. Nor do I add an acid or base, i just use it as mixed to improve the skin tones. I might add that I use 15 ml to tone a 5x7 print,using the toner as a one shot. This guarantees consistency.

koraks
4-Oct-2016, 01:01
Thanks for responding; I occasionally use a thiourea good toner, but I'm curious if anyone else also uses a thiourea sepia toner.