On Thu, 10 Feb 2000, Ray Moth wrote:
> I've wanted to share this idea for some years but never got
> around to it. Like all the best things, it's simple!
[snip]
> Then it dawned on me - the water from the tap was "hard", i.e.
> contained minerals that were deposited on the film as the result
> of evaporation when it was hung up to dry. The solution was
> obvious: do a final rinse of the film with distilled water
> (readily available from car accessory stores for use in topping
> up accumulator cells). This cured the problem for me!
You know, as a technician in a chemistry teaching lab, I spend a
distressing amount of my time trying to tell undergrads about the
virtues of de-ionised[1] water for washing up, so perhaps it's not such
a no-brainer after all.
I've been doing this myself for a while now, and I'd make just one small
alteration: when you've finished the (tap water) washing, do a couple
of short, half-volume rinses (with thorough agitation, swilling
round etc.) with the de-ionised and then a full rinse
with de-ionised. If you just rinse once with de-ionised there will
still be significant mineral content from the drops of tap water left in
the tank (esp. in a very hard water area, like N. Bristol), the two
little rinses will dilute that to almost nothing.
Being a lab tech, I make up my process chemicals with de-ionised too, of
course. Considering the cost as a proportion of the cost of the
chemicls & film, I think it's worth it.
[1] Distillation is just one way of separating water from dissolved
minerals (ions) There are others - most of the stuff you buy from
filling stations etc is probably de-ionised by reverse osmosis, which is
vastly more energy efficient and often produced greater purity.
--
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