KRST: Hypo included - why?
I've had a look around and can't find out why selenium toner has hypo added.
I mean, you fix the print, wash it, hypo clear it (optional), and then dump it in yet more hypo with the selenium toner... Seems odd, so there must be a logical reason for the hypo in selenium toner, but what? Anyone know? Do you really need it?
I have no idea why people do this but many do. I think it is counter productive in that hypo after selenium toning acts as a 'stop bath' and halts the toning effect. Hypo IN selenium toner seems to me would act as an inhibiter.
Originally Posted by Bob F.
If you can't find the answer in APUG then it probably is a really dumb question.
Using an incredibly accurate scientific instrument - my nose - Kodak Rapid Selenium Toner (KRST) seems to be about 80% Ammonium Thiosulfate. I use 60% Ammonium Thiosulfate to mix up my own TF-3 alkaline rapid fixer. The KRST stock solution snaps my head back it smells so vile as compared to the 60% solution.
Ansel said in The Print that selenium toner requires an alkaline environment to work...maybe its just a matter of Kodak finding the cheapest way to produce the stuff to maximize profits.
This is the first I have heard of this. I thought everyone mixed it with hypo clearing agent - I know, I do. Where are you reading about mixing it with fixer?
Several misunderstandings here, I think!
HYPO and Hypo-clear are two very different things. The first is an obsolete name for thiosulfate, the second is a commercial product used for removing thiosulfate.
Kodak Rapid Selenium Toner - KRST - contains ammonium thiosulfate, and quite a lot of it too! I don't know why, but ammonium thiosulfate is a strong enough silver solvent that I can imagine it will speed up the toning process considerably.
The recommendation to mix KRST with Hypo-clear has been abandoned, but is still printed on the labels AFAIK. I mix mine with water only.
Stop calling any fixer "hypo", and we would all be a lot less confused.
-- Ole Tjugen, Luddite Elitist
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Actually, the KRST stock solution *itself* is about 80% Ammonium Thiosulfate...I think...sure smells that way to me. If correct, this means that all those people so set against rapid fixers have been using it all along if they selenium tone with KRST! Ironic isn't it?
Originally Posted by blaughn
So, should we be giving prints that have already been washed, hypo-cleared, then washed again before going into KRST yet another wash-clear-wash treatment? I've just washed in the past, thinking tha a clear would be a waste of time. In that case, is there any point in washing/clearing prints before toning? I've noticed a purple/brown staining on prints that had not been thoroughly washed, and assumed that this was staining of left over fixer in the print.
I think Thiosulfate (ammonium) needs to be added to Selenium to achieve a Rapid toning.
Tim Rudman has a very good explanation of this fact
Mama took my APX away.....
This has been discussed ad nauseum in the past. The accepted procedure is two bath fixing with hypo (sorry Ole...old habits die hard and I am not about to change). The first hypo (Sodium Thiosulfate) bath includes Sodium Sulfite and the second does not. This is immediately followed (without washing) by toning in KRST. This is then followed with hypo clearing agent (it was called hypo clearing agent for a reason.) and then the print is washed for the recommended period of time to achieve archival permanence.
Originally Posted by Snapper
The second hypo bath (without Sodium Sulfite) is saved for the next printing session and becomes the first fixing bath by the addition of Sodium Sulfite and a new hypo bath (Sodium Thiosulfate) is prepared for the second bath.
If you will follow this procedure, I will imagine the staining you note will be eliminated.
Yup - thanks for clearing that up Ole - I did mean the Am. thiosulphate that is already in KRST (and others as far as I can tell). Sorry about the "hypo" - I was being lazy....
Snapper: according to Tim Rudman (who I am inclined to believe on all such matters!) you are correct about the need to wash. According to his toning book, the two causes of staining are inadequate fixing and carry over of an acidic fix in the emulsion/paper to the toning bath - hence the need to wash. I could not find anything in his book that explained why the am. thiosulphate was included tho'.
Ah... and as washaid/hypo-clear is, I think, alkaline, that would help reduce acidic carry over too which explains why it is sometimes recommended prior to the selenium toner (depending on whose book you read) and am. thiosulphate is also alkaline as Murray points out - so, no acid in the toner please...