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Thiourea based sepia toner question

Buggs

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Hi All,

I know that sulfide toning should be carried out in a separate area from film and paper to prevent fogging. An "odorless" thiourea toner also produces silver sulfide in the print. Should the same precautions to prevent fogging film and paper be taken with an "odorless" thiourea sepia toner?

thanX
tim
 
ThanX Brian.

I didn't think so, but it's not always what we can "smell" that counts. There is not a lot of info on the net about thiourea sepia toning and it looks kind of nice on a print I made. I wonder what the disadvantages are besides softening the emulsion somewhat.

tim
 
I haven't notice any paper fogging due to Thiourea based toners on Agfa MCC 111
 
I've been using Thiourea sepia toners for years, mixing from scratch. You only need 4 Chems; potassium ferricyanide, potassium bromide, thiocarbamide, and sodium hydroxide. Different papers respond differently to thio sepia toning. Ilford MGIV doesn't hold bold color in thio sepia like MGWT does. I'm hoping the new ilford classic paper is better with thio sepia toners.
 
Thiourea solid and solutions should be kept out of the darkroom. Any spillage if it dires and becomes airborne and lands on film or paper WILL cause spots. Better safe than sorry.
 
Gerald,
Good point about airborne chemical dust. Probably a best practice for any darkroom chemical!
 
Brian,

This print I did on Ilford MGIV looks pretty bold to me, but that's always a subjective term. The method has to fit the subject matter I guess.

tim
 
Thiourea and solutions with Thiourea will fog film. Sorry to disagree with some here, but this is a fact.

PE
 
PE,

Could you elaborate plz. Would you take the same precautions as if you are using a sulfide toner with the "rotten egg" smell.
I really don't know much about toners.

thanX
tim
 
Brian,

A question for you. I mixed from scratch the PF version of their thiourea toner. I almost doubled the amount of hydroxide in the working solution to obtain dark browns, which I would describe as dark reddish brown. This also tinted the paper base a cream color. Is this normal? Could it be prevented? I need to do some testing, but thought I could tap your knowledge and save some time and material.

thanX
tim
 
So, how would you perform a test for fogging? Is this why the paper base was tinted in my example?

tim
 

I would guess this is from inadequate fixing. The print must be properly fixed and completely washed before sepia toning. Or it could be cause u didn't wash enough after bleaching. I usually wash for 5 min in running water between bleach and toning solution. Enough to remove all the yellow color from the borders of the print.
 
Brian,

I washed the bleached print ~30 minutes, mostly cuz my water is really cold this time of the year. It looked clear. Inadequate fixing; maybe something I need to investigate. ThanX for giving me some ideas.

tim
 
Thiourea releases Sulfide in the presence of silver halide and thus fogges in exactly the same way. That is all there is to it. The dust and the solutions made of it can leave little black dots or total fog on film or paper if the concentration reaches a critical level. I cannot define that level as it varies depending on the emulsion type. Paper emulsions, in general, are more prone to fogging than film emulsions.

PE
 
I'm assuming paper in its packaging and in the box is ok? Sheets out in a paper safe would be more prone to attack it seems. I've never had a problem with it but Maybe my ventilation is more than sufficient.
 
I haven't used it in my darkroom and I think I will be careful in the future. My dark (multipurpose) room is not the cleanest place!

ThanX for the helpful comments, Brian & Ron.
 
Tim Rudman's "The Toning Book" page 22:

"These thiocarbamide toners have two advantages:
Firstly, they don't smell, so they won't fog your films and papers and your family will still love you."

I certainly don't doubt PE's expertise, but I also don't doubt Tim Rudman's. All I know is that in my darkroom I've never had a problem with Thio sepia toners with proper ventilation fogging paper.
 
There always seems to be a considerable amount of "fog" whenever this subject is raised. I had always understood that if you keep your paper in its black bag and then inside its box even the trad sulphide toner does no damage.

Perhaps those who have had experience of toning can say and please only those with the experience need reply, under what circumstances sulphide or thiourea toner can cause a problem.

It seems that unless we can get down to specific circumstances under which fogging will occur and what precautions we need to take to prevent it, we are condemned to repeat the range of posts we have now and the person asking the question and seeking help is essentially none the wiser so might as well have not asked the question.

I appreciate that it is not always possible to give 100% guaranteed answers but that needs to be our forum's aim.

If it isn't our aim then the forum is part of the problem rather than part of the solution

pentaxuser
 
The best way to think of thiourea is as a chemical container for hydrogen sulfide. When the conditions are right it will release this gas. Most people do not realize that it is very toxic. It is the primary component of sewer gas. Sewer workers have been overcome in a few seconds and death occurs within a few minutes. It also dulls the sense of smell leading people to believe that the danger has passed. Its exposure limit of 10 ppm is the same as that for hydrogen cyanide. As a chemist I have always done my toning outdoors.
 
Yes, I agree with Jerry.

Tim Rudman is referring to H2S or Hydrogen Sulfide released from Sulfide toners. Thiourea does not normally just turn into H2S, but it is "a container" for it! This gas spreads everywhere.

BUT, Thiourea is a powerful fogging agent all by itself but it is limited to contact fog. In other words, H2S can spread just like any gas, but intact Thiourea (read ODORLESS solution or crystals) is a contact fogging agent. Get some on a finger, then stick that hand into a black bag of paper, and you fog as much as the Thiourea can touch as a crystal or solution.

So, if TU solution is on your counter top, and it dries out, then wiping with a dry rag can spread dust throughout the darkroom and can leave black dots of fog on things.

I use TU safely in my darkroom in a sink where all liquid can be dumped or cleaned up. I catch all spills of dust or liquid and I never let it begin to smell like rotten eggs.

PE
 
Photo Engineer said:
Thiourea and solutions with Thiourea will fog film. Sorry to disagree with some here, but this is a fact.

PE
Click to expand...

Ron, I know better than to second guess your photographic knowledge.

I guess I have been fortunate as I haven't had any noticeable fogging to the best of my knowledge.
 
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