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I'll check my notes again Joe.
In the mean time, I found that I have added Thymol at 60C, but I've used IPA. I use IPA because Everclear is illegal in NYS.
The nearest source is NJ.
Joe, I checked the class notes and you are correct. I spoke OTOMH and was wrong. Sorry.
I also found that my personal notes show a wide range of temperatures and amounts of 10% Thymol. So, I am stumped. I've added much more ethanol than 1 drop / 20 ml and gotten good results in other cases. Are you sure it was not glyoxal or that you did not have hardener present at the time?
PE
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I can get everclear here at 95% (190 proof), but can only find IPA at 91%. Go figure. They claim the other 9% is water, but . . . .
I'll try the local pharmacy.
There is no such thing as taking too much time, because your soul is in that picture. -Ruth Bernhard
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Joe;
I checked the Osterman formula and he uses 5 ml of Everclear in about 100 - 200 ml of emulsion with no problem. This is not exact, as I did a quickie scan of the formula, but it is added at 120 deg F.
So, his formula has no problem with it either. I suspect something else is going on.
PE
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 Originally Posted by Photo Engineer
Well, the Thymol eventually evaporates out of the finished, dry coating, but it can help. It is present in packaged sheets and the preservative is certainly present in commercial products. If you open a package of Ilford paper, you can smell the phenol which is what is used as a preservative in their B&W papers. That is so strong and toxic when used in the home darkroom that I don't suggest it, but it is used by Ilford and Schoeller as well in large scale operations. Kodak does not use either Thymol or Phenol. They used equally potent materials. I'll comment on them soon.
However, there is another important fact involved in this that I did not mention earlier.
All batches of fine photo grade gelatins are packed with an assay, just like fine chemicals. Only in this case, it is a bioassay that includes things such as tuberculin bacilli, staph, strep, E. Coli and etc per unit weight. This means that the dry gelatin contains a certain amount (printed on the assay), per specified unit of dry gelatin. Well, when you mix your gelatin in warm water those microorganisms begin to multiply unless you stop them. I don't know about you, but I don't like handling gelatin without some sort of preservative there to retard their possible growth!
PE
Heat treatment not possible? Or ammonia washing?
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Ahtiril, I am not sure of what you refer to, but if it is to the bacterial content of gelatin, there is no sure way to destroy bacterial or fungal spores by methods such that the gelation properties of gelatin for photographic purposes are not destroyed. So, all gelatin is tested for biological contents.
Phenol is an antiseptic and other materials kill (antiseptic) or retard growth (bacteriostat). Residual ammonia is not good for gelatin or emulsion.
PE
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Well yes, that's what I was referring to.
I trust what you say, but is residual acetamide a problem?
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Photographic gelatin is one the world's most purified products. Eastman Gelatine has been able to transition to supplying the pharmaceutical industry because the purity requirements for photography meet or exceed medical and food standards. A bioassay is provided to prove that a batch of gelatin meets stringent industry standards -- i.e. no contaminants found.
Give it a moment's thought. If gelatin grew a bunch of evil organisms when it got wet, how could gelatin be used as a culture medium in a biology lab? If there were biological contaminants, they would rapidly overgrow the desired culture. But no, if you practice sterile inoculation technique, you are almost guaranteed a pure culture. No tuberculosis, staph, strep, or E.coli. I've grown things in a petri dish of gelatin that you don't want to know about, but it wasn't by accident. We don't have to fear gelatin.
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Originally Posted by Athiril
Well yes, that's what I was referring to.
I trust what you say, but is residual acetamide a problem?
Acetamide does not form AFAIK as there is no free acetic acid present, nor do you add ammonia during the making process. Ammonium salts of terminal amino acids could form to the detriment of the emulsion.
PE
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Originally Posted by dwross
Photographic gelatin is one the world's most purified products. Eastman Gelatine has been able to transition to supplying the pharmaceutical industry because the purity requirements for photography meet or exceed medical and food standards. A bioassay is provided to prove that a batch of gelatin meets stringent industry standards -- i.e. no contaminants found.
Give it a moment's thought. If gelatin grew a bunch of evil organisms when it got wet, how could gelatin be used as a culture medium in a biology lab? If there were biological contaminants, they would rapidly overgrow the desired culture. But no, if you practice sterile inoculation technique, you are almost guaranteed a pure culture. No tuberculosis, staph, strep, or E.coli. I've grown things in a petri dish of gelatin that you don't want to know about, but it wasn't by accident. We don't have to fear gelatin.
Unfortunately, all of my samples come with analysis that show some "bugs" present, but at what are considered safe levels. In the bio labs, these gelatins are mixed with boiled water and are heat treated to destroy any residual microorganisms, but during emulsion making we do not start with boiled water nor do we heat treat the gelatin. In fact, we do not use masks and gloves. As a result, our emulsions are far from "sterile" and therefore use of biocides is very useful. So useful in fact, that just about everyone uses them including (as seen above) carbon printers. Others who use raw gelatin also find it useful to preserve their gelatin.
No, we do not need to fear gelatin. We need to be able to keep it for a reasonable time though. That is the purpose of a biocide.
PE
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