PA Gelatin: Helpful starting points and tips?

Hi there everyone,

So, after a few years of working with the "noodling" washing method, I am finally seeking out a workflow for coagulation washing.

I was recently able to purchase some PA gelatin from Photo Formulary, but wasn't exactly certain of what percentage of PA gelatin to use relative to the total amount of gelatin. Therefore, rather than waste any silver, I tried a few test of varying quantities sans-silver halides only to discover that the gelatin would not coagulate. To be specific, I tested the following mixtures:

(T1) 2.0g PA gelatin + 8.0g unmodified gelatin + 100.0 ml tap water + ~80% strength Sulfuric acid to a pH of 1 (no coagulation)

(T2) 3.0g PA gelatin + 7.0g unmodified gelatin + 100.0 ml tap water + ~80% strength Sulfuric acid to a pH of 1 (no coagulation)

(T3) 5.0g PA gelatin + 5.0g unmodified gelatin + 100.0 ml tap water + ~80% strength Sulfuric acid to a pH of 1 (no coagulation)

(T4) 9.0g PA gelatin + 1.0g unmodified gelatin + 100.0 ml tap water + ~80% strength Sulfuric acid to a pH of 1 (no coagulation; maybe a bit thicker...)

My immediate theory was that perhaps the gelatin requires the presence of adsorbed silver halide in order for the coagulation mechanism to occur. However, I still didn't want to waste any silver needlessly, so here I am. My question, therefore, is what kind of quantities of PA gelatin are you all using in your emulsions? I realize that there are likely many other factors to consider, such as the formula and type of other gelatin involved, but I need some kind of starting point.

Also, if there are any other tips for coagulation, that would be appreciated too.

Cheers.

Well, PA gelatin takes a long time to coagulate unless used alone with no other gelatin. This is not normal but can be used in teaching situations until the student "sees the light". This is in my book and dvd set both with visual examples.

1. Slowly reduce temperature and pH. Temp to about 30C and pH to about 4.5
2. Coagulum should form and stick to stirring rod.
3. Wash coagulum
4. Redisperse by heat to 40C and pH rise to about 6.5.

The attached photo shows an example of the coagulum from the DVD when it is cold and acidic.

PE

Okay, thanks for the reply.

My question, then, is exactly how long does it take for the coagulate to form? And is there a critical point whereby the percentage of PA gelatin isn't enough for the coagulate to form? I never intended to perform the emulsification with any modified gelatin in the initial reaction, but was instead hoping to just add enough following emulsification to bring it to the desired gelatin percentage, instigate the coagulation process and "stop" crystal ripening.

What you propose is quite reasonable but difficult for a beginner, and that is why I give the instructions the way I do.

A coagulum as you describe your procedure may take hours to form depending on conditions (concentration, temp, pH and etc.).

A coagulum as I have described takes place instantly as you cool and acidify. It becomes tacky like chewing gum and that is it. You can actually lift out the ball of "gum" and squeeze it. With the other method, which is more normal, the coagulum is not a single chunk, but rather, it is a group of chunks or a flocculant.

PE