Elven, yes.. those are really good tips that I found helpful as well.
This does not completely make sense. Think of the early "boiled" emulsions.
PE
Yes, I thought of that as well. So I looked carefully at (for example) the recipes from Eder, in Wall (the key word is “carefully” for all the reasons we take Wall with a grain of salt), and the other recipe sources that I could dig out of my resources.
Here is what I note: The boiled emulsion recipes were, without exception, boiled during first ripening (obviously). In those recipes, the make up gelatin is added as the emulsion is cooled to much lower temperatures or to help it cool down. After make up gelatin is added, the emulsion is either immediately cooled down and set, or ripened further for a short time period like an hour at 95F before setting. This fresh make up gelatin is key to reducing the chances of those old emulsions failing. After washing, at least in that time frame, they went through the emulsion batches pretty quickly, either on a line or a team of coaters coating them the old fashioned way.
The other difference between that era and now is the refinement and quality of the gelatin, which may have an impact (I don’t think so, but it’s worth noting as a difference).
My other thought is that the quality of coatings amongst the manufactures varied widely. As a data point, Seeds had the best quality coating in that time, and based on the comment on ammonia soaking their plates on pg 215 in here
https://nvlpubs.nist.gov/nistpubs/jres/10/jresv10n2p211_A2b.pdf I don’t think they (or Eastman) used a boiled emulsion recipe. This corresponds to my experience in that the conditions which create swirlies also led to a lower quality coating (noticeable difference in the smoothness of the dried emulsion surface, for example).
For us, it seems the time at temperature after make gelatin has been added is important, but that hypothesis requires testing to verify.