Re: a versatile surfactant that kills bubbles

From: Etienne Garbaux <photographeur@softhome.net>
Subject: Re: a versatile surfactant that kills bubbles
Date: Sun, 16 Jan 2005 16:14:59 -0500

> If I may ask, why are you brush-coating gelatin emulsions? For a
> specific look?

That's one reason. Minimally apparent but not annoying degree of
imperfections. When I coat plastic film like Yupo, I have to use dip
coating or wire rod because brush doesn't work well on Yupo.

> Decent results can also be produced with a coating rod wrapped with very
> fine wire. (The original sources said to wrap in a spiral. I found that
> putting a number of discrete "rings" of wire on the rod worked much better.)

I use those for glass plates. I want plates to be coated as perfectly as
possible.

> (I almost always coat
> commercial baryta paper, so there is no need for this.)

If I do that, I'll get something like commercial papers of 20 years
ago, so I don't see a point of doing...

> mylar, it is much easier to start with a product like DuPont Cronar,
> which has a hydrophilic coating, than to try subbing it yourself.

It's practically impossible to coat on poly(ethylene telephthalate)
films like those unless films are pretreated at the plant. But I had
no luck in buying pretreated polyester films so far. (Not that I tried
hard enough so far, though.)

> James Browning, of Digital Mask in New Hampshire,
> published plans for a much more sophisticated system, which is legitimately
> capable of coating mylar film about as well as the Big Boys do it (albeit
> in much smaller quantities).

His coater is impressive. But frankly I don't have space or money to
build one like his.

But no matter what coating method is chosen, there is no substitute
for a good surfactant in many aspects of wet processed photography.

I don't know if you make emulsions yourself, but TL62 in precipitating
kettle allows very smooth mixing of the jet with no worry about
bubbles interfering. Addition of TX200 to the acid jet in desalting by
coagulation method using phthalated gelatin makes nicely big, tight
and stiff curd, instead of zillion of loose tiny particles that stick
to everything and never sink to the bottom.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)