[pure-silver] Benzotriazol Was: Old paper
- From: "Nicholas O. Lindan" <nolindan@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 29 Feb 2008 08:34:24 -0500
"Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
The nature of the fog
centers and development centers produced by light is not
quite the same so the fog centers can be to some degree
suppressed without affecting the light centers ...
benzotriazole
A soliloquy on Benzotriazole - a most interesting chemical.
In addition to its use as an antifoggant in photography, it
has other uses as a metal protectant and may be a substitute/
enhancement to selenium toning for image protection.
BTA forms a water-proof polymer on metal surfaces, which is
pretty neat trick when the BTA is itself dissolved in water.
It is used to protect against corrosion and tarnishing and is
added to glues to increase their bonding strength to metal.
The protection is self-healing to an extent: If the BTA-polymer
it is scratched through to the metal then the next bit of moisture
will dissolve some unpolymerized BTA which will then promptly
cling to the exposed metal. There is a lot of research action
going on in combining BTA with corrosion inhibiting paints as
micro-encapsulated beads that rupture when the paint is disturbed.
My guess is that it's antifog properties arise as the activated
site of a silver-halogen grain promotes BTA polymerization which
protects the site from the developer. Once the developer has
started acting on the site I imagine the BTA is no longer
protective.
I wonder if the BTA forms a polymer coating on the developed
silver strand extruded by the developing site? Are there
any studies of BTA and photographic protection. All I can find
is that BTA has been used by museums as a protectant for antiquities
where it provides anti-corrosion protection without disturbing any
patinas.
At a guess BTA inhibits the action of selenium toner - adding
BTA to the developer prevents color change when toning. To me
this indicates that maybe the BTA does indeed coat the silver strand.
OTOH it may be that the action of BTA preventing the development
of small grains of silver - the reason it gives a cold color to prints -
that is the reason for the lack of color change, assuming it is
the small grains that are responsible for most of the color.
Adding BTA to film developer may give more 'bite' to the grain, when
this effect is desired. Has anyone played around with TX/TMZ developed
in Rodinal/Dektol with the addition of BTA?
BTA is also a UV protectant and is found in suntan lotion, textile
treatments and color photographic emulsions. It shows up in automatic
dishwashing detergent as a silver tarnish inhibitor. It is one of a
large family of compounds including mercapto and thiazole variants.
It even shows up in darkroom timers, where a well known manufacturer
uses it to passivate the front panel against corrosion under the
Lexan overlay.
--
Nicholas O. Lindan
Darkroom Automation - the source of the well passivated f-Stop Timer.
www.darkroomautomation.com
Cleveland Engineering Design, LLC
Cleveland, Ohio 44121
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
- » [pure-silver] Benzotriazol Was: Old paper
