iso propal or everclaear

Well yes, that's what I was referring to.

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

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.

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

Athiril said:

Well yes, that's what I was referring to.

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

Click to expand...

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

dwross said:

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.

Click to expand...

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

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.

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

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.

Now, if there was a simple doctor that would repel cat fur, I'd be really happy!

Photo Engineer said:

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

Click to expand...

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

Washing with acetic acid would probably not form acetamide. It would form ammonium acetate which you would have to wash out.

PE

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

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?

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

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.)

Bill;

We are not contributing to the slaughter of animals. We are making sure the animal did not die in vain by using his very skin and bones to produce beautiful art! You however, are using precious unrenewable resources (OIL) to make those synthetic organic chemicals you use, and you are also causing pollution due to reaction heat and chemical vapors.

PE

Ron,
"unrenewable"? All the dead animal and plant stuff of today will generate more oil for the future. When we run out, that will be temporary. In fact, the pollution I generate today will boost the rate of death for all living things, and thereby contribute to future petrolium supplys.
Lest anyone take my comments to seriously, I do not! I am just a wisenheim. In fact, although I keep trying to be a vegitariaqn, I keep yieldiong to cravings for flesh. I

I hit the send key by accident.
I wanted to say that I always fall off the vegitarian wagon with a turkjey sandwich.