DEAR MARTY,
Well, I am digging back about 45 years into my RIT memory but here is a quick
summary upon which I hope Richard can expand...
1) The longer an emulsion is left to "ripen" after precipitating the silver
halide xtals from the silver nitrate and halogen salt, the larger the AgX
crystals and, as a larger "target" the better chance of being hit by and
absorbing a photon. However, larger xtals also resulted in larger grain, hence
the correlation between higher speed and coarser grain. This is NOT rigorous
physics which would take pages of explanation.
2) It was discovered by accident in the late 19th or early 20th century that
gelatin made from certain livestock bones resulted in a faster emulsion than
emulsion made with different gelatin from different livestock bones. The Kodak
chemists discovered that the faster emul came from gelatin that had larger
traces of sulfur in it, hence "sulfur sensitization" began. Something the cows
ate or drank...literally!
3) Other trace metals and chems (gold, et alia) have also been added when
precipitating the AgX xtals ("doped") which also increase speed. It has
something to do with making it easier for interstitial Ag+ ions to migrate to
the latent image site created by the first photon strike thereby making that
site more "developable". I think sulfur has the same effect.
4) Now, with Tmax technology, most of the above is still true but the AgX xtals
are grown to have a much larger surface area per unit mass so they are even
"bigger" targets to absorb more photons (faster) but, as the mass is relatively
small for that larger surface area, the result is finer grain for equivalent
speed.
I think synapses have fired in my brain that have been dormant for a
looooooooooooooooong time! But I think this is pretty accurate for a layman's
description. I don't think I have forgotten anything but no guarantees!
CHEERS FROM BARBADOS!
BOB
From: "Martin magid" <martin.magid@xxxxxxxxx>
To: "pure-silver@xxxxxxxxxxxxx" <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, August 9, 2017 10:05:18 AM
Subject: [pure-silver] What's in high-speed film?
What is it that makes T-Max 400 different from T-Max 100? Is it more silver, or
what?
What is it that was done in the late 19th century that made glass plates faster
and faster?
Marty
