Digital BW, The Print

Sorry for the cross-post -I put this on archivalcolor by mistake.

My old Random House College Dictionary defines pigment as: A 
coloring matter or substance; A dry insoluble substance, usually 
pulverized, that when suspended in a liquid vehicle becomes a paint, 
ink etc. ...

Well.... There are pigments and there are pigments. Some pigments 
are finely particulate minerals that are for practical purposes both 
inert and insoluble. Some are particulates derived from an organic 
source such as cochineal and may tend to be fugitive. Some azo dyes 
are reasonably "permanent" and others are fugitive (check out a 
Windsor & Newton or Holbein chart of oil or water colors). Point 
being that merely being a pigment is no guarantee of permanence and 
being a dye no guarantee that it will not be more or less permanent. 

In histochemistry it is common to have a chemical reaction produce 
an "insoluble" particulate chromophore at the site of the reaction. 
The "pro-dye/pro-pigment", if you will, is a completely soluble 
chemical substrate, often uncolored, but becomes a "pigment" under 
the proper conditions.

If dye molecules cross link or polymerize when they are "curing" 
they can  take on the physical characteristics of a pigment and may, 
or may not be more resistant to the effects of UV etc depending on 
their chemical structure and they may be insoluble in one vehicle 
and very soluble in another.

I think paint and ink making still has a healthy dollop of 
witchcraft in it and simplistic claims have to be taken with some 
degree of skepticism. Objective testing that describes in physical 
terms (such as delta OD) the effect of time, light and temperature 
on an ink-paper combination under specified conditions, whether it 
be pigment, dye or both  is to my mind the only real arbiter of 
permanence. One rub is that there are no generally agreed upon 
standards of testing for our needs. This leads to our trying to 
interpolate from study to study and try to make sense of what is 
somewhat of a muddle. 

At this point I would be wary of making any firm statements of 
permanence concerning ink jet produced prints beyond a simple 
statement that current data suggests that there will be no fading 
for at least XXX years under specified conditions. To some extent 
that is even true of traditional silver halide prints since their 
permanence is largely dependent upon proper archival processing.  I 
have a friend with a couple of prints by Atget that are brown and 
fading. He has been tempted to try and refix them but then decided 
to leave well enough alone. The only claim  I ever made for silver 
gelatin prints was they were archivally processed and mounted and 
matted on acid free board.

Roger