Re: Calling LIAM RE: update on lumen prints

From: Liam Lawless <liam.lawless@blueyonder.co.uk>
Subject: RE: Calling LIAM RE: update on lumen prints
Date: Thu, 08 Sep 2005 09:39:59 +0100

> It is certain that the
> silver metal will have a surface layer of chemisorbed silver iodide, which
> does absorb in the near UV and blue regions, and it may be a photo-electric
> effect within this semiconductor surface layer that provides the mobile
> electron/hole pair needed to promote the redox reaction above.

I agree with this reasoning, but the lifetime of such a photoelectron
would be very short, and many electron-hole pair would recombine for
no net effect. The hole may bleach a small silver speck but the
photoelectron also tends to be trapped at places in AgX where metallic
silver (or sulfide) is present.

On the other hand, iodide ions themselves are probably reactive with
oxidants and moisture in air over the course of a century, and
products of this reaction may have larger impact on the image silver.

Although this is by no means recommended in practice for various
reasons (such as one in the previous paragraph), if completely
processed silver image is treated in weak potassium iodide solution,
the image will be more resistant to oxidative attacks.
Received on Fri Sep 16 12:05:45 2005