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Photo Engineer
02-28-2011, 08:51 PM
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

JOSarff
02-28-2011, 09:53 PM
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.

Photo Engineer
02-28-2011, 10:04 PM
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

Athiril
02-28-2011, 10:54 PM
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?

Photo Engineer
02-28-2011, 11:09 PM
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

Athiril
02-28-2011, 11:32 PM
Well yes, that's what I was referring to.

I trust what you say, but is residual acetamide a problem?

dwross
02-28-2011, 11:53 PM
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.

Athiril
03-01-2011, 01:01 AM
That's like UHT milk, but once it's re-exposed that's a different story.

http://en.wikipedia.org/wiki/HeLa#Contamination
http://en.wikipedia.org/wiki/List_of_contaminated_cell_lines

Photo Engineer
03-01-2011, 11:23 AM
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

Photo Engineer
03-01-2011, 11:27 AM
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

dwross
03-01-2011, 12:08 PM
As long as we can walk back from "THERE'S TUBERCULOSIS IN MY DARKROOM!!!", I'm a happy camper :). I can settle for a difference of opinion on what constitutes a 'reasonable time' to store emulsion. I stated my reasoning for short storage times in my first post to this thread. I think that my results speak for the soundness of my reasoning, but I also believe implicitly that different people can have different successful workflow philosophies.

Actually, I feel the same way about preservatives in my emulsions as I do about preservatives in my food, and for much the same reasons. I'm not afraid of eating preservatives. I'm 'afraid' of the sense of complacency their use engenders. If I, or the food processors who manufacture much of the food we eat, think that a dash of preservatives will compensate for careless handling or sanitation then it's pretty much certain that handling and sanitation will be less careful than they should be. Yuk!

Question: Is carbon 'glop' a good comparison to silver gelatin emulsions? Protein, carbon, extra sugar...if I were keeping that combo for any length of time, I'd preserve the hell out of it.

Photo Engineer
03-01-2011, 12:35 PM
Well, in this case Thymol is refined Oil of Thyme! So, it is not like some of the preservatives we find in common household items or foods. It is basically more "friendly". It is used in Listerine and other mild antiseptics and does very good in gelatin controlling the bugs that might be present.

All gelatin contains bugs! They grow! The gelatin manufacturers control the level present when it leaves their plant, and then we introduce more again when we use it. They grow. Our job is to minimize it for health and for longevity of our stored emulsions. Coatings do not contain bugs. Just one reason is the fact that a typical hardener is a powerful biocide.

So, we do not have Tuberculosis in our darkroom. No more than we have E. Coli, Staph or Strep!

PE

Vaughn
03-01-2011, 12:35 PM
I keep the carbon printing glop in a hot water bath for up to 8 hours. After that I pour the tissue. If I do not put a fan on the poured tissue for the first 6+ hours, I will get mold growing on the surface of the tissue. Getting the surface dry as quickly as possible keeps the mold away.

As long as this is the case, I will not use chemicals to kill the beasties. I have carbon prints stored in boxes I made almost 20 years ago -- no sign (nor smell) of mold or other beasties growing on/in the prints.

As far as nasty pathogens (TB, etc) in the dry gelatin are concerned -- I think they are in such low numbers that locally introduced beasties from the working environment would eat them up before they could grow into a significant population. Either that or the stink of the local beasties would get too bad to stand before the population of beasties in the dry gelatin would have a chance to multiply into a significant population. Just a guess from a non-biologist.

Hexavalent
03-01-2011, 02:31 PM
Now, if there was a simple doctor that would repel cat fur, I'd be really happy! :)

Athiril
03-01-2011, 02:34 PM
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

I mean washing with acetic acid after said proposed ammonia treatment.. would residual acetamide then pose a problem?

Photo Engineer
03-01-2011, 02:37 PM
Washing with acetic acid would probably not form acetamide. It would form ammonium acetate which you would have to wash out.

PE

Photo Engineer
03-01-2011, 02:43 PM
BTW, I have been mulling over how to answer this statement "THERE'S TUBERCULOSIS IN MY DARKROOM".

I did not say that, nor hint at it. I said that gelatin grew bugs easily. So easily that manufacturers were obliged to report the fact that the levels of any potentially harmful bacteria were at or below approved levels. I gave several examples. Then I said further that given the propensity to grow bugs, it behooves us to be prudent and prevent growth of any bugs in our emulsions or gelatin preparations.

This does not mean that gelatin is dangerous or can cause illness. Rather the contrary. Until it is in our hands it is benign and we should strive to keep it that way.

PE

Ray Rogers
03-03-2011, 04:40 AM
Is there any need to be more afraid at using photo gelatin
than there is at eating a week or so old gelatin dessert?

What preservatives ("I'll comment on them soon.") are Kodak using
in photographic coatings?

wildbillbugman
03-06-2011, 12:47 AM
If you guys would stop contributing to the slaughter of inocent animals just so you can take pictures, you would not have to worry about growing green and blue colonies of bacteria, fungi and, maybe, tadpoles in your refrigerator. I store my non-nutrative, non-sentient emulsions at ambient temperature for weeks with no stentch or little blue mushrooms growing out of them. No thymol. but a idy-bit of alcohol.
GRIN.
Bill

Ray Rogers
03-06-2011, 09:52 AM
Good Food for thought Bill...

BTW
Last year I grew a lovely beautiful yellow mushroom!
(Spores needed for the blues - if anyone has any to share...
"print" exchange welcome.)