Archived posting to the Leica Users Group, 2006/06/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Do not store Xtol diluted. Don't even think about it. As Mike D has pointed out, as the sulfite concentration drops there is nothing to prevent oxidation. Xtol oxidises readily enough at full-strength. >Start with distilled water or water from Portland Oregon especially Mark Rabinor's sink. Portland does have exceptional quality tapwater (and follow to the water quality reports): http://www.portlandonline.com/water/index.cfm?c=cjhfb#soft but wherever Mark's moving to, if he uses Xtol, he may well experience the same kinds of problems others have. I can't find a page that I can read that might indicate what Daniel's water is like, but Scandanavia has plentiful snowmelt and predominantly clean catchments. It does not surprise me that his water is Xtol-safe. Unfiltered tapwater from Adelaide, South Australia, kills Xtol dead. Instantly. If it's not adequately treated I don't even get an image. Really. Metals generally, but divalent cations (those ones with a 2+ for those who can remember their high school chemistry) particularly, appear to make Xtol's activity reliably disappear. In between 'fine' and 'failure' there are a range of semi 'failures' and weird artefacts. The main formula in the patent: http://tinyurl.com/mf7to contains pentasodium EDTA, a chelating agent that sequesters these compounds from being available in solution. The spot syndrome Brian experienced seems to be linked to copper, strontium and some other less common ions in water. Interestingly, Brian told me that his Xtol worked if he mixed it with distilled water but then diluted the stock with tapwater. Dilution obviously works sometimes. Other ions do other curious things and some others also induce 'failure'. There's a useful info page on Xtol here: http://www.covingtoninnovations.com/xtol/ And if you're still scared, there are several excellent alternatives that work similarly. LuGers with experience abound. Mike Durling uses PC-TEA to good effect and John Black's JB9 is the closest thing you can have to Xtol without it really being Xtol, but also has the advantage of excellent oxidation resistance (it is a three-part solution that you mix immediately prior to use) and therefore can be stored for a long time. The difference between Xtol and PC-TEA (and most developer formulae, for that fact) is that the pH is higher in PC-TEA. That's why the patent says 'weakly alkaline'. This influences grain, probably. I tend to agree with Daniel's 'buy Xtol and use it all up fast' theory. Reasonably careful mixing, proper storage and small bottles should keep you safe. If you're really picky, seal the bottles with food wrap after excluding all the air with canned antioxidant. If all that's too much fuss, use something else. Fomadon Excel is the same as Xtol and is still available in 1L packets (it seems the Czechs don't pay too much attention to US Patents - recent EU membership may change that). The Czech packets seem to work very well. Oh, John Black also devised a quick, reliable, tremendously ingenious activity test. I'm sure he'll be happy to share if anyone's interested; but please don't publish it, I still think he should do that himself. -- ___________________________________________________ Play 100s of games for FREE! http://games.mail.com/