[LargeFormat] Help, scratches on negative..
Frantisek Vlcek
largeformat@f32.net
Wed Mar 6 05:52:09 2002
PC> Achal, the advice that has been given to you so far by Uncle Dick et. al. is
PC> excellent, however let me add one comment to your statement about washing.
PC> You do not need "fast running" water. What you do need is to change the
PC> water periodically, with slight agitation (or constant preferrably) in
PC> between.
PC> How you accomplish this depends on the method you decide upon for
PC> processing. If you are going to use metal hangers in a tank. Then use the
PC> same tank for washing. I would think that 20 complete changes of water in
PC> the tank, with 30-60 seconds of agitation in between, would result in fully
PC> washed film. You might be able to get away will fewer changes of water, but
PC> it's better to err on the side of more and it depends on the quality of your
PC> wash water.
PC> Regards, Pete
Hi,
wrt washing - yes, running water is not actually needed. However,
the best washing method is by turbulent washing - that is water
from small jets spraying over the neg, that's what the big labs
use(d), it saves water as well, and is the most efficient method,
but hard to DIY... I normally use the Ilford Archival method for my
negs of all sizes (no LF yet, though - I am still a lurker <g>),
with about doubled the amount of steps, to be on the safe side.
I can't omit to recommend some hypo clearing agent, it can really
speed up the washing and make the negs more archival - I use plain
DIY solution of sodium sulfate (200g per liter of stock solution)
and sodium bisulfite (15g per liter), mixed together in 750ml tank,
added water to make 1 liter, that's stock, it gets diluted 1:10
for use. The bisulfite is simply a preserving agent for the
sulfite, as the bisulfite oxidizes more quickly preventing the
sulfite from oxidizing. What it does is it attaches to Ammonium
thiosulfite salts in the emulsion and changes them to more
easily washable salts, which wash more easily out of the emulsion.
Of course it works only if you use rapid fixer, but nobody uses old
acid fixers anymore, no? They are the worst for archivality anyway,
it should be a crime using them for good negs <g> (it can form
almost unwashable complexes with iodine salts, which you almost
can't wash out). This clearing stuff works for thiosulfite fixers
whatever they are for negs or papers, it's basically the stuff
Kodak sells as hypo clearing agent (they add much more small
quantities of some other chemicals to it, though). It's very cheap,
just mix it in the open though (SO2 gas can be produced). It
significantly changed my washing times. Also, it's proven that
distilled water is not so good for washing, as the things
in the water actually help washing out the salts in the emulsion. However,
if you have too hard water, some deionizer would be probably good.
A good but simple test for presence of any fixer salts (actually,
just sulfite salts) in the washing water is to drop few crystals of
KMnO3 (Hypermangan - the small crystals which make the purple
disinfecting water solution, household chemical) into some water,
and add some of the washing water - the solution of KMnO3 is
purple, if there are any sulfite salts it instantly precipitates
into yellow sediments or changes colour to dirty yellow. It's a
dirty test though, without knowing exact numbers, but still useful.
HTH,
Good light,
Frantisek Vlcek