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Photo Engineer
06-14-2008, 01:08 PM
I have recently been re-reading a rather rare and excellent textbook on photography, "Fundamentals of Photographic Theory" by James and Higgins, and ran across something interesting.

Earlier, I had stated here that there were basically 3 types of gelatin known in the early years of emulsion making, Soft, Medium and Hard "blooming" gelatin related not to Bloom Index, but rather to their ability to sensitize emulsions via the sulfur finishing method described in early patents using allyl thiourea. I had also stated that modern gelatins were oxidized and contained no sulfur sensitizing compounds. This is our modern inert gelatin.

Well, it seems that the inert gelatin we use today was also known as an apparent natural product at the turn of the century (19th to 20th) and known up to the mid 40s of the last century. James and Higgins note that early emulsion makers used any gelatin of these 4 types (not 3 as I had originally stated) in any manner that suited them such as in the make, in a post make addition, and in a final "ripening" step. So, such early formulas are totally ambiguous and J&H warn in their book to beware of such ambiguity.

I have reviewed Wall and Baker both, and find no mention there of any classification of gelatin although they would be virtually forced to know this if they were to make a useful emulsion. This very fact makes me feel that there was less than full disclosure in these books.

My contact with the German Agfa formulas from the 40s indicate that the Agfa engineers knew of 4 types of gelatin, at least... schwerreifend, mittelreifen, kraftigreifend and weichreifend, although English texts only refer to 3, except for the reference above.

Therefore, I again warn potential emulsion makers to beware that the gelatin designations in most all English texts do not convey the full import of gelatin type and usage. Any gelatin can be used at any time.

Modern emulsions take the following general divisions in the make:

Precipitation - inactive gelatin
Ripening - heating with no silver halide solvent or sulfur compound
Digestison - heating with a silver halide solvent but no sulfur compound
Finish or chemical sensitization - heating with a sulfur compound or a sulfur + gold compound.

Any of the above 4 can be combined in any fashion, but the emulsion maker with experience can see this just by reading the formula.

Old formulas use the first 3 terms interchangably and we cannot clearly distinguish what is going on unless the gelatin type is clearly stated as is done in the German Agfa formulas for example. Old English texts do not clearly disclose this for some reason.

I suspect that all of the early authors were being coy about their formulas even in publications. The general readership would not know the difference, and the engineers at the major companies would just be amused.

This is intended to alert those who rely on old texts for information. You might make an emulsion, but the speed, contrast or the amount of silver needed to reach a given result might be far off from what is possible with the 'right' formula.

I would also like to add that many of these formulas include "finals" which are things like pseudo surfactants (Everclear) and hardeners (chrome alum), but in fact, many additives were reserved for overcoats which were necessary to the final function of the photo material. Most of us do not use overcoats, and adding these chemicals to the emulsion layer can often be harmful, and as a result, even the best coating sometimes does not perform up to what is reported as a 'result' in the early textbooks where many coatings had overcoats.

These are some general precautions regarding earlier texts as explained by J&H and also by my re-reading of many formulas. I hope this helps some of you.

PE

Kirk Keyes
06-14-2008, 04:37 PM
Thanks for digging that up. There's a 2nd edition of that book - I wonder if they addressed this issue in that edition? (I don't have either - yet!)

rmazzullo
06-20-2008, 08:08 AM
Hello PE,

Can you please tell me what section of the book that references this? I want to find this in my copy of the book and read more about it. I am curious if there is any mention of this in the Mees and James book.

Thanks,

Bob M.

Photo Engineer
06-20-2008, 08:27 PM
Bob;

Try reading from page 25 onward!

PE

dwross
06-24-2008, 01:30 PM
Hello PE,

Can you please tell me what section of the book that references this? I want to find this in my copy of the book and read more about it. I am curious if there is any mention of this in the Mees and James book.

Thanks,

Bob M.


Hi Bob,

I know you're as fanatic a book collector as I am. If you have The Theory of Photographic Process by Mees, 1942 (1945), look on page 98. Mees talks about four 'classes' of gelatin there.

I can't find any similar reference in the James and Higgins that Ron mentions, but I don't have all the editions (yet! as Kirk says). I love the old books and I don't think I'd be making emulsions today without their guidance.

Keep on collecting!
d

Kirk Keyes
06-25-2008, 12:58 AM
Mine are being shipped as we type. They were cheap enough I got both editions.

Kirk Keyes
07-08-2008, 02:49 PM
Bob;

Try reading from page 25 onward!

PE

Is it a lot of pages onward from page 25?

I've got both the 1948 and 1960 book, and I don't see where you're finding this. Or maybe I don't know enough to read between the lines...

Photo Engineer
07-08-2008, 04:38 PM
Oh, page 25 is near the middle of the chapter on gelatins, and they describe the 4 types of gelatin and mention that one is inactive in that text forward to the end of the chapter. It is pretty much as Denise states in the Mees book she references above. In both cases, the reference is weak. They make no strong mention of it, but merely note it in passing even though the impact is huge today. I suppose they did it due to confidentiality or the fact that the 4 types were common knowledge.

PE

Kirk Keyes
07-08-2008, 08:14 PM
1948 ed. - Chapter 2, "The Photographic Emulsion", page 25, mid page has the heading "After-Ripening".

"Moreover, batches of gelatin which were very similar in their usual physical and chemical properties sometimes would differ enormously in their photographic properties, as measured by the sensitivity of emulsions prepared from them."

Is that what you are refering to? Where does it mention "4 types" of gelatin. 1960 ed. covers "silver halide" and "Preparation of the Emulsion" on page 25.

Photo Engineer
07-08-2008, 08:21 PM
He mentions that there were several used and mentions the inert gelatin just as Mees does. Since I have been able to actually find 4 varieties in searches, I feel that they may have been aware of 5 different types rather than 4, but he does not mention them specifically by name, just that there were some that changed sensitivity and others that did not. The German literature is more revealing than the English literature on this subject.

James is very circumspect in his assertions, as this new method of inert gelatins was just being published in the literature.

PE

Neanderman
07-08-2008, 09:37 PM
There's a 2nd edition of that book

Wiley published what appears to be a 3rd edition, "Introduction to photographic theory", by Carroll, Higgins & James, 1980. (I say this appears to be a third edition because on the rear DJ overleaf it says that Higgins "co-authored the first two editions of Fundamentals of Photographic Theory.

I have a copy and will look through it to see if it adds anything.

Ed

Photo Engineer
07-08-2008, 09:58 PM
That is very odd. I knew Burt much better than the other two and he never mentioned that to me. There is no mention of that in any of the books I have either.

I've mentioned elsewhere that Burt and his wife used to vacation at Letchworth state park where we also used to stay at the Glen Iris inn. We spent many hours together on the front porch discussing photo theory and product design. This is one thing that he never mentioned even though James and Higgins often came up in our conversations.

PE

Photo Engineer
08-25-2008, 02:00 PM
To further this discussion about gelatin, first off in the OP I mention the remarks about gelatin. Well, in the section on ripening the authors refer to using an inert gelatin to make the emulsion and an active gelatin to finsih the emulsion after washing. They give no details, but Kodak engineers and Agfa engineers among others knew of at least 3 if not 4 types of active gelatins. So the subject was quite well known at the time.

Now, to move to modern times we see somewhat the same thing. I have been buying brand "A" inactive oxidized gelatin and recently changed to brand "B" inactive oxidized gelatin. I observed a 1.5 stop speed loss in my Azo type emulsion!

This indicated to me that there is a change in the emulsion introduced by some ingredient in the gelatin so I heated up emulsion A and B and then coated immediately. I also coated at 2 hours and 8 hours with constant heating at 40 deg C applied for all of this time.

The results are in the photos attached.

The surface defects you see are artifacts due to being coated on unsubbed paper. The sample photo on the left shows gelatin A and B side by side fresh, and the sample photo on the right shows gelatin A and B side by side after 8 hours holding in the sink. It is evident that sample B did not change in fog substantially but did gain a bit in speed and/or contrast over 8 hours. This indicates 2 things to me.

One is that gelatin A has a weak ripening agent in it and is not truly a pure oxidized photograde gelatin as we know it today. It is a weak ripening gelatin as was known 50 years or so ago. It causes fog as well as increased speed.

Second is that gelatin B has no ripening agent.

Finally, the emulsion B, through the small change it undergoes, tells me that I need more stabilzer or a longer ripening time during the original make (or both).

Since my coating sessions rarely last more than 2 hours, I saw little or no change with respect to hold time from either A or B in normal coating sessions, but I did see the unexplained speed difference in fresh coatings, and this long keeping test revealed the reasons for the speed difference.

Gelatin B is Kodak photograde gelatin and is sold by the Photographers Formulary. IDK who else sells this, but I have verified it with them.

They change to Gelatin B, when I began to have hints of problems last year with Gelatin A. Gelatin A is still a good quality product, it is just different. And so, to make an emulsion using the methods of James and Higgins, one might precipitate an emulsion with gelatin B (Kodak) and then add A to make up to final coating weight and hold for 1 hour or more at 40 - 60 degrees C as described in the text.

This will conclude my tests, as it is much preferred to use a gelatin of type B (Kodak) and add the precise amount of sulfur containing agent rather than rely on a gelatin to supply it, as the amount of sensitizer might vary too much and would take extensive tests to qualify a gelatin of type A to be useful.

PE

Ray Rogers
08-26-2008, 12:18 AM
[QUOTE=Photo Engineer
I have been buying brand "A" inactive oxidized gelatin and
recently changed to brand "B" inactive oxidized gelatin...
Gelatin B is Kodak photograde gelatin...
Gelatin A is... a good quality product... just different.
PE[/QUOTE]

What was Gelatin A?

Photo Engineer
08-26-2008, 08:42 AM
What was Gelatin A?

Ray;

I don't feel comfortable posting the name publicly. I am concerned thought about differences between this gelatin and the Kodak variety in other alternative processes.

PE

dwross
08-26-2008, 11:28 AM
Ron,

A question about your statement: "The surface defects you see are artifacts due to being coated on unsubbed paper." The only commercially available 'subbed' paper I'm aware of is the glossy baryta that The Formulary sells. Is there another? Or, are you normally subbing watercolor paper before you coat?

Which paper are your tests printed on? If it is cold press Strathmore, you might consider changing to something smoother or giving your coating bar a bit more of a gap. I know you like the heavier paper because it dries flatter, but I think you'd have better luck judging the density range on a smoother paper. Fabriano Artistico HP works well. And for the purpose of jpeg illustrations, the PF baryta might be best.

Also, re the various gelatins out there: People may have missed what I think you meant to say - that most problems with materials (and the absolutely inevitable mysteriously-changing-product phenomenon) are alleviated by an intimate knowledge of your process, whichever it may be. With practice and familiarity, it's easier to do tweak-arounds.

d

Photo Engineer
08-26-2008, 11:49 AM
Denise;

This is a Strathmore hot press paper. The defects are not visible to the naked eye as such. Rather, the paper has a pleasing tapestry like look and feel. The scanner magnfies this. You have seen some samples like this at the workshop and the above ones look no different (fresh) in the dmin area.

PE

Ray Rogers
08-26-2008, 01:50 PM
Ray;

I don't feel comfortable posting the name publicly. I am concerned thought about differences between this gelatin and the Kodak variety in other alternative processes.

PE

Ron,

By other alternative processes, it sounds like you mean non-AgX processes like carbon tissues, cyanotype or even perhaps AgX Matrix film....

I wonder if a simple description of the material and the behaviour you are concerned about would not be sufficient to protect those other alternative-process users?

If "Gelatin A is still a good quality product... just different."
Seems unnesessary to neuter the nomenclature.

What promted the change to Gelatin B anyway?

Kirk Keyes
08-26-2008, 02:25 PM
If "Gelatin A is still a good quality product... just different."
Seems unnesessary to neuter the nomenclature.

What promted the change to Gelatin B anyway?

I think it's that Gelatin A fogs and is not truly inert - as it should be and for which it was being sold as. While Gelatin B is inert.

I think I would have to disagree with the statement that it is a "good quality product" if it did not meet one of the primary characteristics it was supposed to have.

It still can be used for other uses for which gelatin can be used, but just not as inert gelatin.

Photo Engineer
08-26-2008, 02:28 PM
I have described the differences above. Higher speed with gelatin A, and a high tendancy to go into fog with keeping. Those reasons assisted me in suggesting the change! My guess as to higher quality was paramount in this suggestion. I have tested several gelatins from different companies. My recommendation is Kodak gelatin, 250 bloom photo grade bovine oxidized and deioinized.

PE