Sulfur finish increases speed and contrast of an emulsion. In an enlarging speed emulsion, it is usually added at 100 mg of Hypo (pentahydrate) per mole of silver. This is based on grain size, and so a finer grained slower emulsion would need more and a coarse grained emulsion would need less.

You bring the emulsion to 60 deg C, add the hypo solution while stirring, and heat for 1 hour. You then cool. This is a normal operation, but temperatures may vary as well as hold times.