[Leica] Darkroom Help...fingers

[William Gower <w.gower@home.com>]

Bill Harting wrote:

> Does anyone else use fingers?

When I first started processing, I used 2 household sponges. Then I happened
to luck out by getting some more advanced training. The first tip I was
taught was:
 
"...(use your) fingers when wiping negs, as they are the only things that
you know are going to be clean."

The proviso being that you wash your hands really well after handing fixer.

Now, I do a 1 minute soak in deionized water (or distilled) water, a few
drops of photo-flo, hang to dry, then I put my hands in my pocket, and leave
the room, go for a walk, etc. I don't touch until they are dry. No scratches
yet.

If you use a decent distilled or deioizned water, the photo-flo isn't
necessary, but it helps remove the excess droplets of water. There shouldn't
be any significant amount of solids in the distilled water to leave a
residue (a water spot).

Photo-flo isn't black magic. It's simply a surfactant that breaks the
surface tension of the water molecule, causing it to sheet and run off the
negative's surface, rather than bead and dry with a "spot".

Some people use an alcohol rinse in lieu water/photo-flo. Alcohol's are less
polar than water, and have less surface tension. Alcohol's won't form well
defined droplets like water will - i.e. alcohol's readily "sheet".

Here's a trick - put a drop of water on a clean glass plate, then put a drop
(of equal volume) of a water and photo-flo solution beside it. Now get down
and look at the relative heights of the droplets. The water only droplet
should be high and spherical; the the water/photo-flo solution will be
relatively flat in comparison. A drop of alcohol should look like a big blob
on the plate and form a poorly defined drop.

William

 - and if you REALLY care, surface tension has the SI units of millijoules
per meter squared (mJ.m-2).