Re: APIS, hydroquinone hardening

From: "Christina Z. Anderson" <zphoto@montana.net>
Subject: Re: APIS, hydroquinone hardening
Date: Thu, 14 Jul 2005 09:41:38 -0500

> Martin, so our silver developers that contain hydroquinone harden the
> cornea? Bummer...is there no safe hardening agent out there? How about
> chrome alum?

Hardening reaction itself is an aggressive reaction to the host
molecules, which are not too dissimilar from protein molecules we
have. So hardeners are by definition highly reactive agents... Some
hardeners are a bit easier to handle but they come with all sorts of
other problems.

> Ryuji, re: fog, if it completely hardens the gum layer applied then
> it would be useless, but if it just hardens a bit of the layer that
> is in contact with the paper, then that could just be developed out.
> That's one thing gum has going for it--it is not a one shot deal.
> There are always variables along the way. The only way I'll be able
> to find out is when my hydroquinone order arrives from B and S. But
> your point about glut hardening slowly and not instantly is an
> important one.

That would depend on how much excess hydroquinone is contained in the
sized paper. Hydroquinone is water soluble and diffusible through
paper and gelatin layers when the paper is wetted by the dichromated
gum coat. So I'm worried about this effect as well.

Glutaraldehyde is actually a very rapid hardener if the rate of
crosslinking reaction is compared to that of formaldehyde, glyoxal or
chrome alum. It's simply that we are using much smaller amount of
glutaraldehyde in more dilute stock solution to take advantage of its
superior hardening properties with gelatin, so that our exposure to
the hardening agent is minimized. This is better approach for the
safety of the users as well.
Received on Thu Jul 14 08:55:29 2005