From: Ryuji Suzuki (rs@silvergrain.org)
Date: 09/28/03-09:40:15 PM Z
From: Kate Mahoney <kateb@paradise.net.nz>
Subject: Re: coating method Part 2
Date: Sun, 28 Sep 2003 22:04:34 +1200
> What are you using for a surfactant?
Triton X-100 or PhotoFlo 200. PhotoFlo 200 contains some propylene
glycol in addition to Triton X-100 but it doesn't seem to affect
much. PhotoFlo of higher concentrations (600 and 2000?) omit propylene
glycol but Eastman Kodak doesn't seem to supply them in small sizes.
Reed and Jones say copious amount of PhotoFlo is called for, but I
think a few drops for 30ml is enough. Speaking of Reed and Jones, they
recommend to add too much glycerol. Also, I find emulsion formulae by
P. Robbins specify too much sulfur sensitizer.
I made a emulsion conditioner to be added immediately prior to
coating. The formula is roughly as follows:
3 parts 2.5% glutaraldehyde solution
4 parts glycerol
1 part PhotoFlo or Triton X-100 solution adjusted for similar concentration
and 8ml of this is added to 200ml of emulsion. (or 1ml to 25ml emulsion)
I have found that addition of glutaraldehyde by itself may make
localized clots of gelatin and this is undesirable. When glycerol
(glycerin) and glutaraldehyde is pre-mixed like this, and added in a
thin stream while stirring the emulsion, I have found that the amount
which can be added has a wider latitude. However, when too much of it
is added, the emulsion becomes excessively (uselessly) viscous or even
solidify in several minutes.
I'm trying to locate Kremer Anti-foam. When I find it, I'd probably
add a few drops of it to this conditioner. (This provides convenience
as well as dilution as suggested by Judy Seigel.)
I have found dishwashing soap (the stuff to apply to the sponge to
clean dirty dishes) to work very well for cleaning glass, to which
emulsion is coated. The emulsion is conditioned with the additive
described above. I purposely maltreated test plates but it was
perfectly fine, even with less than perfectly dried plate emulsion,
regular processing with non-hardening fixer and running water washing,
as long as I didn't touch the coated side.
Coated glass is best chill set in freezer for several minutes, and
then dried in a fridge (best) or at a room temperature.
I also found that wiping the cleaned and dried glass with PhotoFlo
diluted with isopropyl alcohol immediately before coating to help
adhesion of emulsion. But I think trace amount of residue from
dishwashing soap is adequate and usually this step is unnecessary.
> Did you use actual silk in the screen or a polyester??? Maybe it
> would make a difference. Forcing the emulsion through the screen
> obviously created little air pockets that form bubbles as you lift
> it off..can't think of any solution to that one. Maybe the emulsion
> doesn't need glutaraldehyde to print with a screen but rather would
> be better thinned a little?
Clearly, I was an ignorant of screen printing process. Terry told me
that there should be a clearance between screen and the material to be
printed (coated), so that only the part where squeegee is applied
should be in contact with the substrate, thereby making the screen
self releasing. Without any viscosity the emulsion would run away
without the help of the squeegee and is not a good idea. So I'll be
trying this next weekend.
I use a screen made from something like polyester, definitely not the
silk.
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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