If I can add another 2 cents - even the AJ-12 formula, which is fairly explicit in detail (compared to many other 'old' formulae), contains some fuzzy areas such as "Heat the emulsion to 15 minutes at 130 F (55 C) for further ripening; then slowly cool it to 104 F (40 C)." How long is "slowly cool"? 5 minutes? An hour? All the while, there is activity in the kettle which will affect the final result. Another, but not so critical item: "Soak 1 ounce 180 grains (40 grams) of gelatin in cold water until it is thoroughly softened. Pour off excess water ". What is 'thoroughly softened'? How much water should the gelatin absorb? Similarly, the noodling/washing procedure does not specify temperate, or what kind of water (tap water, distilled, DI). As I have learned, overwashing can ruin an emulsion, by diluting it and/or rendering it unstable.
Originally Posted by Photo Engineer
Can such a formula be followed exactly as written? The formula part: almost. The procedure: kinda. Frequently one encounters frustratingly vague phrases like "in a manner familiar to one practiced in the art". Whatever one's interpretation of the 'grey areas' of a procedure, it's good policy to aim for a manageable and reproducible set of parameters. i.e. always use the same water, use a chill bath instead of "slowly cool", and do it the same way every time.
Fortunately, the home emulsion-maker is not likely to be growing t-grains, or using complex dopants, so there is a fair amount of wiggle room in procedure that will still yield a pleasantly usable brew. The magic of seeing a home-brewed and coated glass plate is nothing short of thrilling!