Marco B
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Hi all,
I have been using a two bath bleach-redevelop sepia toner for quite a while now with success. It is a ferricyanide bleach / thiourea combo. Now I always assumed that the bleaching step was a vital step in doing sepia toning with thiourea, although I am aware that there are direct single bath sepia toners as well (polysulfide, for the difference, see here: http://81.207.88.128/science/photo/toners/sulfide.html).
I assumed thiourea by itself would not be capable (or hardly at least), of toning a print. But here's what I observed recently:
I had a series of 4 photos I needed to tone. I toned the first two, but, contrary to my normal practice of rinsing the prints after the second thiourea bath in plain water, I was a bit lazy and decided to drop them back straight into the tray having the 2 remaining prints to be toned.
When I took out the third print to be toned, and put it in the ferricyanide bleach, I noticed that contrary to expectations, the bleach did not seem to attack and work immediately on the highlights, as it normally would. I was a bit stunned. The print seemed to resist the bleach. When I left it in there longer, I noticed that the process of bleaching started, but seemed mainly concentrated on midtones and shadows. When I quit the bleaching and rinsed it, I was surprised to see that actually, the highlights were almost not bleached, while normally, they would be the first to be bleached. Midtones and shadows were.
I than realized, that, contrary to my expectations and thoughts, the two already toned images, and the carry over of thiourea solution, must have sepia toned the highlights (zone 7 up to maybe beginning or half zone 6)...
This was a big surprise, not only because of the direct toning action, but also because of the very low concentration of the thiourea toner already capable of doing this. I always wait quite long to have the solution run of the prints before moving them to the next tray, the same here, meaning the amount of carry over of thiourea solution must have been low, and diluted in almost 6 liters of water (I printed 16x20 inch). And that still managed to sulphide / tone almost the entire zone 7 of the print... I did not see a noticeable difference in tone by the way, meaning that it was not a full toning, but still.
Please note that I always rinse well inbetween the bleaching and thiourea toning bath, so I am pretty sure the amount of bleach possibly active in the thiourea bath, must be absolutely minimal (if bleach even survives the thiourea bath), so it seems a direct toning effect of the thiourea.
I also noticed a difference in the final color of the image. I prefer to only partially bleach back my images, as I like the deeper still black shadows caused by that. While sepia toning using a partial bleach / redevelop step can lead to a kind of split tone (highlights zone 7 sepia, midtones and shadows almost neutral), the pre-toned prints had a more "overall", equalized toning appearance (even though still not fully toned). The tone was actually very pleasing and slightly more dark reddish, instead of more orange / brown with the normally toned first two prints.
Now this raises a few questions:
- Is the bleaching step really necessary with thiourea toning ? (I am assuming a thiourea bath with sodiumhydroxide accelerator, as toning with just thiourea is also possible, but slower). I guess it is still a matter of speed, with pre-bleaching allowing maybe far faster toning, but I am surprised by the speed with which the strongly diluted "carry-over" toner managed to tone the still untoned prints.
- Are there people who have done a direct single bath toning using thiourea alone, if at all practical?
- Are there people who actually have used this phenomenon as an "alternative" strategy for sepia toning, to achieve other tones?:
* drop print first in thiourea toner for a first small toning step
* rinse print
* drop in ferricyanide bleach
* rinse
* back into thiourea redeveloper
Marco
I have been using a two bath bleach-redevelop sepia toner for quite a while now with success. It is a ferricyanide bleach / thiourea combo. Now I always assumed that the bleaching step was a vital step in doing sepia toning with thiourea, although I am aware that there are direct single bath sepia toners as well (polysulfide, for the difference, see here: http://81.207.88.128/science/photo/toners/sulfide.html).
I assumed thiourea by itself would not be capable (or hardly at least), of toning a print. But here's what I observed recently:
I had a series of 4 photos I needed to tone. I toned the first two, but, contrary to my normal practice of rinsing the prints after the second thiourea bath in plain water, I was a bit lazy and decided to drop them back straight into the tray having the 2 remaining prints to be toned.
When I took out the third print to be toned, and put it in the ferricyanide bleach, I noticed that contrary to expectations, the bleach did not seem to attack and work immediately on the highlights, as it normally would. I was a bit stunned. The print seemed to resist the bleach. When I left it in there longer, I noticed that the process of bleaching started, but seemed mainly concentrated on midtones and shadows. When I quit the bleaching and rinsed it, I was surprised to see that actually, the highlights were almost not bleached, while normally, they would be the first to be bleached. Midtones and shadows were.
I than realized, that, contrary to my expectations and thoughts, the two already toned images, and the carry over of thiourea solution, must have sepia toned the highlights (zone 7 up to maybe beginning or half zone 6)...
This was a big surprise, not only because of the direct toning action, but also because of the very low concentration of the thiourea toner already capable of doing this. I always wait quite long to have the solution run of the prints before moving them to the next tray, the same here, meaning the amount of carry over of thiourea solution must have been low, and diluted in almost 6 liters of water (I printed 16x20 inch). And that still managed to sulphide / tone almost the entire zone 7 of the print... I did not see a noticeable difference in tone by the way, meaning that it was not a full toning, but still.
Please note that I always rinse well inbetween the bleaching and thiourea toning bath, so I am pretty sure the amount of bleach possibly active in the thiourea bath, must be absolutely minimal (if bleach even survives the thiourea bath), so it seems a direct toning effect of the thiourea.
I also noticed a difference in the final color of the image. I prefer to only partially bleach back my images, as I like the deeper still black shadows caused by that. While sepia toning using a partial bleach / redevelop step can lead to a kind of split tone (highlights zone 7 sepia, midtones and shadows almost neutral), the pre-toned prints had a more "overall", equalized toning appearance (even though still not fully toned). The tone was actually very pleasing and slightly more dark reddish, instead of more orange / brown with the normally toned first two prints.
Now this raises a few questions:
- Is the bleaching step really necessary with thiourea toning ? (I am assuming a thiourea bath with sodiumhydroxide accelerator, as toning with just thiourea is also possible, but slower). I guess it is still a matter of speed, with pre-bleaching allowing maybe far faster toning, but I am surprised by the speed with which the strongly diluted "carry-over" toner managed to tone the still untoned prints.
- Are there people who have done a direct single bath toning using thiourea alone, if at all practical?
- Are there people who actually have used this phenomenon as an "alternative" strategy for sepia toning, to achieve other tones?:
* drop print first in thiourea toner for a first small toning step
* rinse print
* drop in ferricyanide bleach
* rinse
* back into thiourea redeveloper
Marco