Re: DuPont Velour Black AND POP

From: BOB KISS <bobkiss@caribsurf.com>
Subject: RE: DuPont Velour Black AND POP
Date: Mon, 18 Jul 2005 12:22:52 -0300

DEAR BOB,

During high intensity exposure, reciprocity law fails because many
tiny and undevelopable latent subimages are created instead of a few
developable latent images. This is because many photoelectrons are
generated in very brief time and they make their own latent subimages,
instead of "slowly" growing latent images that are already present. I
don't think chaning developer type can be a lot of help here.

Most modern emulsions are well corrected for this problem, when high
intensity exposure is expected. Typically, AgX crystals are doped with
agents that create deep electron traps that release electrons slowly,
such as iridium. There are a few other things that are commonly done
to reduce HIRF (among other goals).

I hear some people complaining about Dektol but I have not seen any
convincing evidence that glycin develoeprs work better. Dektol is a
versatile developer, where you can adjust it for many applilcations by
changing dilution and by adding KBr and sometimes benzotriazole or
other agents. In other words, you may need a bit of tweaking to pull
the optimal performance out of this developer.

The difference in fog you observed may be because of developer
concentration, pH or bromide concentration. I think Ansco 130 1+1 has
2.5g/L or so of KBr while Dektol 1+2 has about 0.7g/L. Dektol has
rather minimal amount of bromide for a print developer, especially
when the solution is diluted for normal use.
Received on Mon Jul 18 11:58:33 2005