Wayne, the Hydroquinone would be part of a specially formulated developer, not part of some bleach. There are two common ways to achieve selective tanning:
PS: I have never done this process, so I would be the very last one to be asked for sample recipes. Ned's blog appears to be what you should be looking at, and the two links I provided in this thread point towards HQ based tanning developers which have at least been tried.
- Use any developer to develop the image, then use a bleach which tans gelatin wherever metallic silver was bleached. That's the approach chosen by the process using the dichromate bleach.
- Use a developer which tans gelatin wherever development takes place. This is what Pyrogallol, Catechol, and apparently also Hydroquinone based developers can do, if they are formulated correctly. No bleach should be necessary here as long as the developer creates sufficient tanning.
Avoid any spills.
The bromoil process requires the selective hardening of the gelatin
Wayne, I think you are on an interesting path. Your idea is to achieve the selective hardening during development of the print rather than after the print has been developed. I don't want to speak for Jerry but I think his comment was simply a general one and true: the main objective is to obtain selective hardening of the gelatin, there aren't that many ways to achieve it, and to work well for bromoil it needs to be robust. That's pretty hard to do! I know with my own experiments, I always get some gelatin relief image, but the ones that are really strong are easier to ink. There seem to be a lot of variables at play and sometimes I get a strong relief and sometimes a weak relief after seemingly repeating everything the same... this tells me there is at least one critical factor ( temp, humidity? I don't know! ) that matters a lot but that I'm not controlling.
BTW I also don't use dichromates, mostly because I don't know how to deal with waste (including washes ) ...
but a quick Google turned up a patent that calls developer hardening "comparatively rugged and durable" although I don't know what its being compared to. Since I have never done bromoils I also don't have a sense of just how "durable" the relief must be.
https://www.google.com/patents/US1923764
When I read these patents, it sounded to me like heat might be a promising way of enhancing the hardening if it's too weak.
With bromoil, sometimes people don't soak the matrix long enough before inking, so that the unhardened gelatin doesn't swell enough and reject the ink.
It may also be worth mentioning that the soaking time is also dependent on the temperature and vice versa to get the differential of hard and soft gelatin within the print.
The main problem with pyro is not so much its toxicity (which is represented by LD50), but that it's absorbed through the skin. Skin exposure is a much more common occurrence in typical dark rooms than ingestion or inhalation.Hydroquinone must be treated with care too but its much less toxic than pyro. Some have tried to argue otherwise (always pyro proponents) but I've researchd it pretty well and satisfied myself with that conclusion.
I did a fairly meaningless experiment last night, just to see what happened and to use up some old stock. Using the hydroquinone/sodium carbonate version of Pyrocat-HD linked to above, I took 175 ml of Part a and 250 ml Part B and added 500 ml water. My rationale if you can call it that was just to get in the ballpark of 10grams HQ and 40-50 grams carbonate/liter just to make sure I got an image with the least time wasted. I don't know what amounts would be desirable for best tanning. I only made 2 test strips and one "final" print. I was pretty darned pleased with the image, but as expected the solution oxidized rapidly in the tray turning almost black in 15 minutes. I used Oriental RC paper, which isnt suitable for bromoil but seemed adequate for this quick experiment to see if I could get a useable print developer. Anywho I got apretty nice warm toned image with good contrast that was overall quite pleasing, but a fair bit of general stain too on the borders. I'm not sure if a couple grams of sulfite would have reduced the general stain or prolonged its life, but I knew any more than that would prevent image stain so I didn't add any. I'm not sure if this method has any actual potential but I was bored and needed to get rid of some solutions before heading away from my darkroom for a month or two.
I just got some copper sulfate, with the idea of using it to bleach some prints ala bromoil and try a few ideas about hardening. I also am playing with another process and need a bleach step.
Two questions:
1) why do they use copper sulfate instead of pot-ferri for bleaching bromoils?
2) I know that some people make bromoils from modern "super hardened" paper, but I don't know what the trick is. It would be nice to be able to run some tests w/ inexpensive paper. Maybe this will all wait until I make some gelatin emulsion, which will probably happen before pigs grow wings....
Try reading the conversation that ensues after this post: Dead Link Removed
Gives ya an idea regarding dichromate.
finally reading this thread again
and the dichromate article is gone
anyone know where it might have popped up?
unfortunately mr peabody, sherman and their way back machine
can not help due to robot txt whatever that means ...
No, it just moved.i guess its lost forever then
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