Re: Daguerreotypes again-mercury

From: Etienne Garbaux <photographeur@softhome.net>
Subject: RE: Daguerreotypes again-mercury
Date: Mon, 23 Aug 2004 22:50:31 -0400

> Indeed! It was known at the time that silver halides were light sensitive,
> but what leap of logic made him ask, "What would happen if you suspended an
> exposed silver iodide plate in mercury vapor?"

Discovery of development in Daguerreotype is said to be accidental,
when he left an insufficiently exposed plate in his chemical cabinet
and found images was visualized later. He repeated the same
experiment, but by removing some of the chemicals each time, and
finally identified mercury vapor was responsible for development of
the image.

On the other hand, Calotype used acid pyrogallol solution fortified
with silver nitrate, which is a physical developer, more similar to
"silver intensifier" solution (like Kodak IN-5) than commonly used
chemical developers. It took many years to realize alkaline pyrogallol
without silver nitrate was a better (chemical) developer, which was
after silver gelatinobromide plates. But then, a race was started to
search for a new, better developing agent.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)