If the coated paper is dry (important) and perfectly sealed (also very
important) it should last a minimum of several months. I read reports
of carbon papers (gelatin) that would last over a year and such papers
are more prone to fog than dichromated gum papers.
Note that pre-sensitized gum papers used to be commercially available.
This, and the patents to make them are described in _Gum Dichromate
and Other Direct Carbon Processes.
>
>2) Do I remember correctly somebody saying that you can brush the sensitizer
>on the paper first and then spray on the gum/pigment later? Don't the two
This technique was invented by the original inventor himself, Alphonse
Poiteving, and was patented Feb. 15, 1856. Of course, the same idea
"invented" many times later:-) For more on this, consult the above
mentioned book, available in thousands of libraries.
If you use a spray gun to apply the emulsion you should wear a mask,
avoid all heavy metal colors (lead chromate, etc.) and avoid the
dichromate sensitizer in your emulsion. Pre-sensitize your paper in a
solution of dichromate.
Best results are usually achieved with a freshly coated emulsion that
contained everything, including the sensitizer. There is room for
experimentation though.
Luis Nadeau
>suffer from not being mixed ahead? Does the sensitizer still manage to combine
>with the gum? (Of course, the spray method would be advantageous for
>smoothness, and separating the two solutions would mean less wastage when
>using non-artist airbrushes.)
>
>I appreciate any feedback
>Olivo