Hi Bill,

T.Thorne Baker has a recipe in "Photographic Emulsion Technique", 1st edition, p.108, where he adds erythrosin to converted silver immediately before precipitation. I haven't gotten around to trying that recipe yet, but I always trust Baker. That said, I add half my erythrosin 2/3 of the way through digestion, and the other half as a final. No particular reason. That's just the way two dozen variations of trial and error blazed the path to my final, favorite ortho recipe. My guess is that you can add erythrosin just about anywhere in the process. (Caveat: remember, all recommendations here are for gelatin emulsions. All bets are off with synthetic carriers.)