Ok, Erythrosine can be added after pptn. to AgCl emulsions. If added to AgBr or AgBrI emulsions, the full effect is only seen if it is added before pptn. If added after the potn. is complete, then you get 1/2 or less of the full effect.

This is shown in Mees along with comparisons with other dyes.

Also, if you add too much after pptn. you can lose the inherent blue speed of the emulsion. This does not happen if you add it before pptn, as the excess washes out. You essentially get the right amount all the time if added beforehand.