[pure-silver] Re: You're making your own emulsion!
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 31 Dec 2004 15:51:37 -0500 (EST)
From: "Gene Johnson" <genej2@xxxxxxx>
Subject: [pure-silver] You're making your own emulsion!
Date: Fri, 31 Dec 2004 08:12:50 -0800
> I know your emulsion has been mentioned before, but I just thought
> I'd take a moment to say bravo! That's pretty darned
> impressive. I'd love to see a scan or two.
Thanks - I should have some surviving test strips that I can scan.
I don't know how much a scan can convey, though.
My homemade papers are hand coated on watercolor or printmaking paper
of 300 g/m^2 weight, and they make a perfect holiday's greeting
card. So most of good ones were disposed of that way :-)
I started vaguely playing with the idea of making my own emulsion at
the beginning of 2003. I needed to rent a dedicated darkroom to
realize this project (I'm a renter, and I had a darkroom at the corner
of my residence, where I could print only during night). I found a
space and about to sign the lease but the guy was a total asshole and
refused to do the plumbing work at the last minute, even after I put a
lot of building out work. So I had to find another place, which took
many months. I moved in to my current place August 2003. Finding the
right space was more than half of the problem. If you already have a
light tight garage with running water, it is possible to make emulsion
in house.
In chlorobromide emulsion, it took me some work to make emulsion fast,
high contrast and absence of fog. Chlorobromide emulsion is very
sensitive to impurities from anything, and also react with many
things. It's a great trouble because paper sizing has to provide very
good chemical barrier to prevent emulsion form touching the
paper. Otherwise, the print will be pure black, Dmax everywhere. But
it is worth the trouble because the tonality is different from bromide
papers. The emulsion contrast also responds well to different
development techniques in tray, unlike many modern commercial materials.
In bromide emulsion, it is absolutely essential to remove reaction
byproducts in the middle of emulsion making process. This process is
called desalting or washing. Without this process, chemical
sensitization process to boost the speed and contrast will be greatly
impaired. Traditionally, this was done by gelling the emulsion to
stiff jelly, cut it into noodles, and soak it in cold water for
several hours with many changes of water. This is exactly the same
idea as soaking salted codfish (a Portuguese favorite, but possibly also
Scandinavia as well.) in water for two days with several changes of
water before cooking. I had to improve the efficiency of this step in
order to make "production" quality plate emulsion without hiring a
technician, which is not an option for me. I read great many times
this old Kodak patent (expired), which chemically modified gelatin so
that it can be made insoluble as desired, and can be solubilized
again. The method worked in principle, but when I tried, it worked
very poorly. I think the patent was hiding one important step that
must be used in order for that method to work well. Well, knowing that
the method should work in principle but doesn't work in practice, I
started varying parameters that are not described in the patent, and I
finally found what was missing in the patent. After that,
experimenting plate emulsions became a lot easier.
Bromide emulsions require this troublesome desalting step, but the
emulsion is generally more robust and easy to handle than chloride
emulsion. With the idea of making prints with my existing negatives, I
started this venture with chlorobromide emulsion without knowing the
difficulty. If anyone is interested in starting the emulsion venture,
I recommend to start with a bromide printing emulsion. If you screw
up, the most likely error is too low a contrast as a printing
emulsion. That way you can use it as a very slow plate emulsion!
After figuring all these, I read the history of Fuji Photo Film. The
company had bromide paper when the business started in 1934 (it was a
spinout of a celluloid company, to which a dry plate company
merged). But commercial chlorobromide paper had to wait for many
years. It seems that it was not just me who had extra trouble by
trying to chase this difficult animal. AGFA had a decent chloride
paper by WWII. The formulae for AGFA Lupex printed in post-war
intelligence report have traces of how they managed the problems.
By the way, another pure-silver participant Terry Holsinger also made
his plate emulsions.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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