>>Do you have any ideas of the principle or principles involved.
Of the various direct carbon and gum papers mentioned in my last post I
have only general information regarding the coating procedures of two,
Artigue and Fresson.
Artigue -- Literature of the period suggests that Artigue paper was
manufactured by allowing fine pigment particles to settle on paper coated
with wet gelatin. This operations was carried out in a dusting box. The
image was developed with a water/sawdust mixture, as Fresson.
Fresson -- It is clear that Fresson papers have several coating. Luis
confirms this, as will microscopic analyis of a cross-segment of Fresson
paper.
There are perhaps many ways to make good direct carbon papers. Some of the
early literature suggests that a paper with exposure and developing
characteristics similar to Fresson could be made by coating a piece of
sized paper with several layers of pigmented colloid, each varying in terms
of pigment density. If each of the layers were of a different sensitivity,
with the most sensitive and least opaque coating on the bottom, and the
least sensitive and most opaque coating on the top, it would be possible to
make a print with a full tonal range. The theory behind this is similar to
that used in making multiple-printing gums.
No facts or experimental work here, just conjecture based on text research.
Sandy King