Re: Do dichromates change with age?
On Mon, 14 Jul 2008, Loris Medici wrote:
That could have been me.... maybe 10 (or so) years back, they emptied out a closet of old chemicals at Pratt, and through some chain of association a very large, somewhat antique-looking bottle (like maybe 1920s) maybe 1/3 full of ammonium dichromate, came my way -- and seemed to work fine. I didn't test its speed against the more recent one I'd been using (and who knew how long that had been in the bin at the supplier before I bought it?), but it seemed to work about as usual, and, since I generally develop by eye, I let it go at that. I probably have some of it around still, but my studio has piled up like the Mississippi delta... not sure I could find it today, or that I didn't rebottle in smaller container....I remember reading someone (British?) using NH4Di (maybe it was KDi) as old as 30 - 40 years in the list archives but I'm not sure...
However, one possibility that comes to mind re why speed could change is --- could it be water supply? Here in NYC the folks at the pump house have a very creative streak and tend to add ingredients ad hoc, depending on the weather, the season, the leaf mold, the feeds, and who knows what else.
Or, if you're getting your water from pure mountain stream, that could vary by what the farmers sprayed that week, what traffic, weeds, dredging, et al, obtained... and 40 other things I never heard of...
Or maybe the temperature of the water -- as in summer?