new unit of measurement discovered!

Peter Mumford (103007.3432@compuserve.com)
22 Mar 96 12:42:44 EST

I have lately been making platinotypes. I have been using the method outlined
by John Rudiak in a two-part article in View Camera magazine (Jan & July 94).
This is an excellent and simple method, involving measuring solutions with
pipettes instead of drops, and hydrogen peroxide (H202)as a restrainer instead of
chlorate. The only difficulty I had was trying to find a 1/10th ml.
micropipette. Apparently they are obsolete. The micropipette is used for
measuring very small volumes of peroxide - in cases where, for example, one drop
of 3% H202 might be far too much, like when making up a sample of sensitizer
for a test print.

So I developed a new unit and method of measuring that has proved
useful. I made up a series of solutions of H202 in distilled water: 1/2%, 1%,
1 1/2%, 2%, 3%. Now the peroxide can be added to the sensitizer in units of
DROP-PERCENTS. For example, one drop of two percent H202 contains two drop-
percents of H202. For me, this works out so that two drop-percents added to the
amount of sensitizer needed for a 4x5 test print (.36 ml) corresponds to a
#2 paper grade, and one drop-percent gives a #1 grade, etc. When I make up the
sensitizer for the full size print, I keep the ratio of sensitizer to restrainer
identical to my test, ie for a grade #1 print, with 2.7 ml of sensitizer, 7.5
drop-percents are required. To keep the measuring accurate, I always use the
same dropper for H202 solutions. I dont know if drop-percents will be useful
in other applications than platinum printing, but there they are.

Peter Mumford
Seattle