I have decided to describe emulsions in terms of 3 classes.

The first is the "Old" or "Art" types which date from about the start of Silver Halide in Gelatin to about 1945 and are partly documented in books by Eder, Baker and Wall. They are filled with error and misdirection and also filled with myths due to the lack of science in their work. Results using these formulas can vary wildly.

The second is "Recent" dating from about 1945 to about 1970 and these show a remarkable mix of old and new where emulsion making was undergoing a huge transition and combined old and new methods. Makes of this type can vary but are more stable batch to batch. Methods used here on "Old" emulsoins work and improve the results. In fact, some of the "Recent" formulas are "Old" formulas updated.

The third is "Modern" which dates from about 1970 to the present day. These are typified by tightly controlled making run by computers with predictable results just about every time. The methods used to make these emulsions need their own specific equipment.

Now, here is the problem. I can write any of these types down on paper and compare the methodology for you, and all of the above are in print (BIOS and FIAT Reports, Wall, Baker, Eder, etc), but they all lack some critical data in print or are filled with obfuscation. But, the Modern" emulsions are more clearly delineated in some recent patents. BUT - none of the modern work says anything about the means by which the emulsion is chemically sensitized or as we call it "finishing". Yes, I have found that I can make a "Modern" emulsion, but I don't know how to finish it! I was never an expert on this and did not start work on finishing until my last year at EK.

And, searching my notes, I find that I have notes on exactly one emulsion finish given to me in preparation for design of a modeling and scaling program for the finishing process. Here is the catch. A typical modern emulsion make takes about 10 steps and up to 3 hours. A finish takes up to 30 to 40 steps with exotic coded chemistry, ramps up and down in temperature and addition of Silver Nitrate and Sodium Bromide during the process. There are also changes in pH.

So, I have decided that one of the major barriers to achieving results close to Modern emulsions would be replicating the very confidential methods of finishing the emulsion with Sulfur, Gold, Acid, Base, Antifoggants and Heavy Metals.

I thought you all might be interested in this line of reasoning. I find it interesting and it will probably remain a secret unless one of the experts in the field decides to come forward. I talked to one not too long ago, and he was more interested in getting a new roof on his house than discussing these types of things. I can fully understand his position, as life must go on and there is not that much interest here for the "real" nitty gritty of the emulsion making process.

I guess that we will be stuck with Sulfur, Gold and Heat!

PE