Re: making regular photo paper POP

From: Ben Coburn <btcoburn@silicodon.net>
Subject: Re: making regular photo paper POP
Date: Thu, 01 Sep 2005 12:22:42 -0700

> This is the first I've heard of producing colors on BW paper with
> such a simple process. Can anyone comment on how the colors are
> actually produced? Is it something like butterfly wings, where
> exceedingly fine structures trap and reflect specific wavelengths of
> light?

Small particles of silver metal tend to scatter light of some colors,
and this is why extreme fine particles in warmtone images look
brown/orange/yellowish. But they can also look green or other colors
depending on the size/shape/crystal structure/etc.

Those interested are recommended to look up "Mie theory" for more
details. In printing out process, the image silver is in shapes not
too dissimilar from sphares and the theory is going to give you good
insight into the image color.

However, in real world pictorial materials, there are a range of
crystal sizes mixed in the emulsion. Also, in developed out
silver-gelatin image, the silver is actually in the form of filaments
and this is a deviation from the Mie theory and therefore the relation
between the image color and size becomes far less clear-cut. After
all, there is no universal theory that can relate the hue of silver
image to grain morphology. There are several more detailed accounts
than the straight Mie theory, but they all have some limitations.
Received on Thu Sep 1 13:43:46 2005