Re: Yupo, yucca paste and emulsion

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, January 31, 2004 12:02 AM
Subject: Yupo, yucca paste and emulsion

> For those who don't know, yucca paste is the creamy stuff
made from
> starch of yucca, mainly served with rice and stew in
Brazil.
> (Brazilian people - feel free to elaborate)
>
> From: Sandy King <sanking@clemson.edu>
> Subject: Re: Yupo, was Re: Temperaprint & Gum
> Date: Sat, 31 Jan 2004 00:10:46 -0500
>
> > I may try Pete's suggestion and add a bit of colloid to
the
> > sensitizer and try again. Would this make the coating an
emulsion?
>
> I guess you and most people know this, but the term
"emulsion" used in
> silver gelatin process is entirely a misnomer. It's just
that everyone
> knows silver gelatin emulsion is actually a dispersion, it
just
> doesn't matter what it's called, and the misnomer never
got fixed
> (though I occasionally persist in saying dispersion, or at
least being
> reluctant in using the term emulsion). Mayonnaise is an
emulsion, some
> salad dressing are emulsion, the real hollandaise sauce is
an
> emulsion. Silver gelatin sensitizer, yucca paste, the
liquid part of
> the Chinese egg drop soup or sweet and sour soup,
thickened sauce of
> stews made with connective tissue rich cuts cooked near
boiling point
> for hours (collagen breaks down to gellatin in such a
condition), many
> fake hollandaise-like sauces are dispersions, not
emulsions. Emulsion
> involves tiny droplets of fats, water, or both. Aquaous
phase of
> gelatin or starch may give thickened texture but does not
involve
> droplets of fat or water.
>
> Many silver gelatin literatures use term "emulsification"
to mean what
> is correctly called precipitation. This is clearly also a
> misnomer. There is no emulsification going on. You have to
stir the
> reacting vessel during precipitation stage, and you'll get
an instant
> milky appearance as soon as you let the jet (buret or any
apparatus
> providing one of the reacting agent, usually silver
nitrate) flow, but
> it's just the appearance, and the amount of stirring is
nothing
> compared to the vigorous stirring needed to make
hollandaise
> sauce. Real emulsification would typically need a lot more
vigorous
> stirring. (You could make hollandaise emulsion much
easier if you
> added Kodak PhotoFlo 200 and antifoamer before adding
lemon juice, but
> it's probably considered inedible)
>
> Ok enough on another piece of useless information that
doesn't let you
> do anything new. As long as it is clearly understood that
it's a
> misnomer and people know what's right, one can call
anything an
> emulsion but that would void the word. I personally think
it's
> sensible to avoid incorrect use of emulsion altogether in
a small
> attempt to break the chain of nomenclature misuse.
>
> --
> Ryuji Suzuki

  Many years ago I attended a SMPTE meeting where the
Technicolor process was discussed. The Technicolor people
kept refering to "the emulsion" in a puzzling way. I turned
out that they meant the _support_ not the sensitive layer,
which they called something else. I am not sure about the
nature of cellulose nitrate or acetate, perhaps it is a true
emulsion. Anyway, the Technicolor people explained that
photographic emulsion is actually a dispersion and that
company practice was not to call it an emulsion. That
confused the stuffing out of everyone there.
  This point is made by C.E.K. Mees in his famous book on
photographic chemistry. He says that while photographic
emlusion is not an emulsion the practice of calling it that
was so well entrenched that to try to change it in his book
would only lead to confusion. So emulsion it remains
whatever its true nature. Older books on photographic
chemistry, particularly British books, tend to use
terminology dating from the days of alchemy. There is a web
site giving modern chemical names for ancient terms.
http://dbhs.wvusd.k12.ca.us/Chem-History/Obsolete-Chem-Terms1.html
  Perhaps somewhere there is some bacon of selenium to go
with the liver of sulphur.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com