Recommended sources for photo-grade gelatins
Okay, I know I can get good 250 bloom ossein gelatin from Bostick and Sullivan. But where can one buy non-industrial quantities of softer gelatin, such as a 170-180 bloom, that are pure enough to use in photo applications?
BTW, what bloom rating does Knox gelatin have? And isn't it a porcine gelatin?
I can only add that the Formulary sells Kodak (Eastman) photo grade 250 BI gelatin.
Why would you want the lower bloom. It is thinner in viscosity and hardens at a different rate. But it is not as different as 75 BI gelatin. The Formulary can get 75 BI or 175 BI gelatin, but you would probably be the only customer. I have about 50 pounds of 175 BI gelatin. PM me if you are intereste in a sample of it or pig gelatin.
Knox, AFAIK is bone gelatin.
Maybe Clay wants to experiment with different grades of gelatin. You, yourself, said that our predecessors had used different grades of gelatin. Baker has a negative recipe on p.81 Photographic Emulsion Technique, 1st ed. that specifies soft gelatin.
Originally Posted by Photo Engineer
There are two approaches to making emulsions. Either you can wait until someone hands you a recipe, and hope it works, because you haven't a clue what to do if it doesn't, or, you can dig in and reach beyond the cookbook. It is when one can get past the 'paint by numbers' approach, to learn the whys and wherefores of the fine controls, that the potential of handcrafted is realized.
Best of luck (and yes, even fun) to you, Clay.
Thanks. I figured this would be the place to ask specific gelatin questions. I actually need the softer bloom for another process, however.
Very important note here for emulsion makers
The SOFT GELATIN referred to in Baker is not related to Bloom Index, it is related to the amount of sulfur present in the emulsion in the form of allyl thiourea. This is an example of where Baker is more thorough than Wall, but also where terminology changes can cause errors.
Originally Posted by dwross
To make things worse, in German it is soft ripening which implies the blooming of a flower. Soft blooming therefore meant low allyl thiourea, not low Bloom Index.
The soft, medium and hard gelatins in old texts refer to the amount of contrast control you have via sulfur sensitization during the ripening step which is caused by allyl thiourea and has nothing to do with Bloom Index which is loosely related to gelatin chain length, amine content, and viscosity at a given concentration.
I have been trying (vainly it seems) to explain this difference.
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And I have be trying (vainly it seems) to express an important tenet of science and an essential one of art: History is fascinating and useful, as are the definitions of what was. But, what we have today is what we have and what we must understand. Understanding comes from careful and creative experimentation, with the mess and waste and false starts accepted as part of the process - and the joy.
So that's the key info there - the gelatins of old, were used and it was determined that one particulat batch of gelatin would produce a paper or film of low or soft contrast, whereas a second batch may produce a paper/film with a high or hard contrast. The batches of gelatin were then labeled "soft", "hard", "medium" or whatever seemed appropriate based on that testing. And nothing related to today's Bloom Index is implied.
Originally Posted by Photo Engineer
That seems pretty straight forward. And I had noticed the reference that Denise mentioned in Baker as well and wondered about it's use there.
Yes, two meanings for the same word depending on specific context and era.
What Clay wants is a soft - medium BI gelatin that is inactive. The definition in Baker referred to contrast control with an active gelatin and was unrelated to Bloom Index. The BI in that era was ignored, largely due to the coating methods, and the ways they adjusted the final melted emulsion before coating. Viscosity and hardening were less important in those days.
Look in the class notes for these definitions Kirk, Denise. They are there.
You have to know historical usage and present usage to prevent misunderstanding and error.
BTW, in German, the old medium gelatin is "Mittelreifend", and they had more than 3 grades! Overcoat in German implies a basting sauce for a roast if you take it out of context. So, reading this in German is often a delight and a revelation. Oh, and actually, Kodak had more than 3 grades as well. I have simplified due to lack of details. All of this was totally out of use and obsolete in the 50s.
From Dictionary of Photography, Wall,1912:
"... Another most important test is its expansive power, for upon this depends to a great extent its frilling or non-frilling properties. The following table of the the chief characteristics of the best commercial brands will be of practical use; but it may be stated that the best film can, as a rule, be obtained by a mixture of one part of hard and two parts of soft gelatine: -"
Wall then goes on to list nine varieties of commercial gelatin by name, e.g. Coignet's gold label special, with their 'character': hard or soft, together with the amount of "water absorbed, times in weight" . Coignet's is hard/ 7-1/2, Heinrich's is hard/8-3/4, Russian isinglass is soft/2-3/4. Wall claims that varieties "1, 3, 6, and 9 are the best to use."
If Wall can be accused of anything, it is of having the hubris to assume that people will have read his dictionary and many other publications before working through his recipes. I don't see him trying to keep secrets. Quite the contrary. He expected people to do their research.
There are several points here.
1. Wall wrote this in the Dictionary of Photography, but in his text with formulas he merely says "gelatin" with no grade specified, therefore making the formula incomplete and virtually unusable even in his time. Baker did the same but included more information such as addition times and temperatures of solutions.
2. The terms in the Dictionary of Phtography are totally obsolete and were by the time of many of his and Baker's texts in the 20s due to the change in terminology. There was no common measurment. No one can, at the present day, interpret the passage you quote due to severe changes in terminology and lack of explanation.
3. His usage of hard, medium, soft and etc are hard to relate to frill or to sensitization as his words are unclear. Remember, the hard gelatins have more allyl thourea which decomposes in the making of the emulsion thereby giving it less gelation properties, and in addition since they used 'boiled emulsions' at the time, these all contributed to changing the ability of gelatin to set up. Actually, low BI and high BI don't necessarily govern frilling as much as the way an emulsion is made, the type of hardening and a numer of other factors.
4. BI was probably not in use during the time of Wall. In fact, I can find no definitive source for it in any chemistry, biochemistry or photography text, and google searches give vague comments about it but no facts. Yahoo searches did find some limited information We did not use this commonly at Kodak. We used the actual viscosity of a given solution. As a term, and as we understand gelatin, BI is rather recent.
Try here: http://www.engr.utexas.edu/bme/ugrad...in%20films.pdf for a modern reference to BI. A search is either recursive back to APUG or you learn that Orlando Bloom has an Index and you can take the test to see what your BI is.
I have no affinity for Orlando Bloom Denise, but you might. No offence intented.
The bottom line is that back then, research into Wall's work was rather fruitless and useless and is even more so today unless you have a Rosetta Stone.