I've read some 500+ posts here about purity grades for some photographic chemicals, mainly borax and sodium sulphite. I followed heated yet informative debates on the subject, from 2007. I'd like to get a better grasp of when a technical grade of borax, sodium sulphite, and sodium carbonate is acceptable to us. My main target is Ansco 130, my standard paper developer, sodium sulphite also into HCA, for paper and film. Ideally, all would be pure enough for film developers, though I'm happy with Xtol. From what I read, I gather a low level of heavy metals is important, as Pb < 0.002%, and Fe < 0.005%. Freedom from water insoluble impurities, which could get embedded in the emulsion, comes next. However, I could not find any statements that explain what makes an acceptable level of insolubles. Can that be expressed numerically, or is it a matter of testing/risking? My apologies, if I have missed a post. There are no suppliers of photo grade chemicals in Ireland, I have to ship everything. I really like Photographers Formulary, but air shipping to Europe of the bulkier chemicals is very expensive. Silverprint in UK don't ship outside of UK. Some European photo suppliers offer technical, or are unclear about their grades. I am resigned to buying higher lab grades, from Sigma Aldrich, Acros, Lennox, or Fischer Scientific of items Formulary will not ship to Europe, like hydroquinone. The bulkier ones, like Na2SO3, are expensive from lab suppliers, $60/kg+. I am not sure what else to do, but to try and understand the purity levels and grades, make the best choice I can, and just try and see what happens. For example, I am looking at a spec of light sodium carbonate (made by Tata), which lists Fe < 0.003%, Pb < 0.0001% (same for As, Cd, Cr, Co, Cu, Mn, Ni, Ti, V), assay 99%, bicarbonate < 0.7%, chloride < 0.3%, and Na2SO4 < 0.04%. Insolubles in Water at 20˚C < 0.02% (or 200 mg/kg if you prefer). For completeness, it also mentions loss on heating < 0.5%, and pouring density of 480 min to 600 max kg/m3. Or, I am looking at Borax, made in Turkey I think, with a less complete spec: Fe < 0.0003%, does not list Pb, SO4 < 0.007%, insolubles in water < 0.008%, B2O3 36.99%, Na2O 16.40% and pH 9.38. Strangely, it shows purity as 101.31%, which doesn't make sense to me. It also shows a sieve analysis of 0.63% at +1000mm and 3.28% at -0.068mm. Or, looking at a food-grade sodium sulphite anhydrous certificate, from NaturalSpices.nl, it all looks good, except it does not list insolubles at all: > 98% Na2SO3, > 49.8% SO2, thiosulphate < 0.1%, heavy metals as Pb < 0.001%, Pb < 0.0001%, Fe < 0.001%, Hg < 0.00001%, As, Cd, Cr, Cu, Ni, Se, Zn < 0.0001%, Sb < 0.0002%, chloride < 0.003%, Na2S2O3 < 0.02%, Na2SO4 is the "remainder". The supplier states, however, that if any anticaking agents where added, they would have to be listed on the certificate. Hmm. I'd be grateful if you could point me in the direction of a better understanding of these grades. Any other suggestions would be most welcome.