Puncture the yolk sac with the knife and let it out into the cup or film canister. Vinegar is used to neutralize excessive yolk fat, preserve it from decomposition and to make dry pigment more mixable with emulsion. If you add too little of it, overly fat paint may crack in time especially when used over leaner layers of paint. Now you know your starting point. Stir emulsion and put it back in to the canister.
All eggs are different depending on the country and climate.
Summer eggs have more fat than winter ones. Egg fat consists of 3 acids - olein, stearin and palmitin. It dries or hardens very slowly. The hardening process may take up to several months. Albumen, and vitellin - are strong emulsifiers.