A bit more on chlorhydroquinone: a formula and discussion: http://www.apug.org/forums/forum222/33800-edwal-111-a.html And another snippet of info: "...I defer to Mees, Tull, Neblette, Hauff, Bogisch, Lumiere, Andresen, Haist and researchers of similar reputation whose reports were both authoritative and accurate, and did not - to the best of my current knowledge - mention anything about hydroquinone image stain. ..." My emphasis. Before I quote something else, I'd just like to say two things: -I'd trust the guys here who say that hydroquinone forms a stain image even if I didn't already know it, and -few of the standard texts (or at least those I have) go into much detail on stain images, if they mention it at all, but they do cover tanning. Tanning and staining may not be the same, but they are similar, and if the developer oxidation product is coloured then there is likely to be a link between tanning and the formation of a stain image. OK, so on to L P Clerc's Photography Theory and Practice, 1971 edition revised by R. E. Jacobson, Vol 4, Monochrome Processing: "573. Oxidation Products of Developers; Tanning; Secondary Images. The quinonoid oxidation products of developers that are formed in the absence of sulphite, or in the presence of very low concentration of sulphite, are deposited in the gelatine at the site of development, and in a quantity proportional to the amount of silver halide reduced. Usually they polymerize, giving rise to coloured, tanning substances of the nature of humic acids, whose exact constitution is unknown. After removing the silver image ... a yellow or brown secondary image remains, which, though it may not appear very intense to the eye, can give acceptable prints on high contrast paper because of its absorbtion of actinic light. The following table (Lumière and Seyewetz, 1928) shows the colour of the secondary image obtained in various developers, its relative intensity and the concentration of sulphite necessary to prevent its formation. Developer -- colour -- relative intensity -- sulphite g/litre Pyro -- yellow-orange -- 10 -- 11 Catechol -- black -- 10 -- 6 Hydroquinone -- yellow-brown -- 10 -- 2 Chlorhydroquinone -- yellow-brown -- 10 -- 2 Amidol -- reddish-brown -- 8 -- 2 p-Aminophenol -- brownish-black -- 3 -- 2 Metol -- brownish-black -- 2 -- 1 PPD -- Grey -- 1 -- 0 Glycin -- None." Best, Helen ................................................. On anti-fog: there is a stronger compuond than benzotriazole: it's called phenyl-mercapto-tetrazole From a private converstaion with Ron Mowry (Photo engineer:) Cor; Sorry, my answers have not been up to par. I've had a bad 2 weeks with flu. The total starting concentration in the developer is 1 mg / liter for a usual case of fog. You can go up or down from there. It is added from an alcohol solution of about 1% or whatever is comfortable. I've used 0.1% and 10% solutions. It really makes no difference. At 1% (1 gram / 99 grams of alcohol), then 1 mg would be hard to measure out. At 0.1% or 100 mg / 100 grams of alcohol, it would be easier to measure out. It is an odorless white powder. The only photo supplier that has any that I know of is the Photographers Formulary, but they have not listed it in their catalog as they only got it recently. It is a very powerful antifoggant, one of the strongest there is. Ron Mowrey Best, Cor