That question was already asked in another thread.

Excess halide retards the sensitization by these ingredients. Having sensitization carried out during precipitation introduces an extra variable into the making process.

Therefore, it is best to add these chemicals after precipitation and then if it an unwashed emulsion to add the chemical or wash and add the chemical.

The chemicals to be added include any one of the following; sodium thiosulfate or sodium thiocyanate, or thiourea, or allyl thiourea with or without a gold salt.

However, with the older emulsions, speed to be gained will only put you into the mid range of about ISO 40 or so at best. The contrast gain may be significant.

Boiling has another drawback, and that is the effect on gelatin. Hours of heating gelatin at near boiling temperatures causes it to denature and lose its gelation and hardening properties. In simple words it falls apart. It really is not a good way to make emulsions.

Please see the other threads on this same topic.