Let me jump in here in the fog discussion.
I have no experience with stored tissues cause I make my own one allways
fresh for printing (pre sensitised as I described).
So I can only talk about this:
My experiences say that we have to distinguish two kinds of fog:
1. Fog caused by carbon technique itself
2. Fog caused by poor working/storing contitions or useless materials
1. I proofed this kind of fog by processing a freshly coated tissue of plain
gelatin without sensitizer on a pice of plexiglas ( to avoid any kind
of chemical reaction with final). The result was an absolutely even
and very thin layer of pure gelatin where the tissues was in contact with
plexiglas. I made it visible by inking it after development.
What we can say is the more pigment a certain amount of gelatin contains,
the more fog (of this kind) the tissue will produce and vice versa.
To avoid this kind of fog, let me call it a >basic layer of gelatin<, I
mention to give the pigment paper a second very thin top coat of plain
gelatin. This second layer will not influence the graduation or
highlight density cause you expose simply through the pure gelatin.
In practice, I think, this method has no practical advantage, because
the amount fog described here caused by typical carbon formulas can be
neglected. Typical for this kind of fog is that it is limited to tissues
format and very even and that it cannot be reduced by prolonged
developement, heavy agitation or higher temperature.
2. The second kind of fog is more interesting for us. It is caused by a
certain amount of undefinite hardening with takes place in the emulsion
caused by:
- poor storing conditions
- overworked sensitizer
- useless pigments
- useless paperbase or final (chemical reaktions)
- lond drying times
- heat (eposure)...
Avoid this factors will eleminate or at least reduce fog problem.
Typical for this kind of fog is that it is on the hole final, uneven
(caused by hardened gelatin/pigment-slime in developing water whith
adheres then on the finals surface) and that you can reduce it by heavy
agitation several changes of water, prolonged development or rising
temperature.
That s what I found out, hope its helpfull for this discussion
Stefan Stecher