From: Robkin, Eugene (erobkin@uwc.edu)
Date: 02/15/01-08:20:03 AM Z
I have to take some exception to the idea of trying to make cellulose
nitrate on a small lab scale.
First of all cellulose nitrate dissolved in things like acetone along with
some other stuff is an old fashioned airplane fabric coating called dope.
You may be able to find it in some model airplane shops. Just be sure it is
not the more modern coating which is cellulose butyrate (which I may have
misspelled). Its great virtue is that is shrinks like mad when it dries and
thus makes the fabric coatings drum tight. The more modern stuff works
better and is much safer.
Second ether is worse than inflamable, it is violently explosive when mixed
with air. The advice to have a fire extinguisher handy is correct but it is
for the people who will rush into the room to pick up the pieces. You
yourself will not be concerned anymore with putting out the fires.
Finally, I don't know a thing about coating glass plates from my own
personal experience but I happen to have a copy of E.J. Wall's book
Photographic Emulsions: Their preparation and coating on glass, celluloid
and paper, eperimentally and on the large scale. Published in 1929 by the
American Photographic Publishing Co. On page 163, in the chapter on glass
plates, he claims:
"The older substratum [that's for coating plates, E.R.] was a solution of
potassium or sodium silicate, water glass, but this is apt to fog the
plates. A much better solution is
Gelatine 5 grams
Chrome alum 0.5 grams
Water 1000 cm
The plates should be dipped bodily into this solution, at about 20 deg to 25
deg C (68 to 77 F), and then stacked on a rack to dry. The coating left on
the glass is extremely thin, but quite sufficient to make the emulsion
adhere well."
This is a pretty simple formula. The alum is there to make the gelatine
waterproof. I suppose that other things would work as well.
He also recommends the old standby dichromate sulphuric acid mix for
cleaning. I've worked with that stuff myself and it is nasty to handle but
it really cleans glass. It also removes skin very well. There are better
home methods.
Eugene Robkin
This archive was generated by hypermail 2b30 : 03/06/01-04:55:39 PM Z CST