Normal household ammonia will do, I think. I used a strong version, but can't
look it up right now because I am not at home.
Just to make sure: The addition of ammonia is only recommended, if for some
reason you MUST wait more than 5 hours or so after drying before exposure and if
the tissue would fogg otherwise. The best sensitizer I find is pure dichromate,
in distilled water, if you think your water is of doubtfull quality. I have
tried several additives that were recommended in the old literature and usually
the medicine is worse than the disease.
Klaus Pollmeier