DO NOT EXPOSE THESE PLATES TO THE LIGHT FOR A LONGER TIME THAN IS
NECESSARY.
The pigments used in the preparation of these Plates are the most
durable known, those which have been proven unstable having been, as
far as possible, discarded. The latter include carmine and other
cochineal lakes, colors of vegetable origin (as gamboge, violet
carmine, indigo, etc.), and most of the aniline or coal tar dyes,
though among the last are a considerable number which are really more
permanent than several colors habitually used by artists. Certain
colors in this work could not, however, possibly be reproduced except
by the employment of pigments which are more or less sensitive to
_prolonged exposure_ to light, and hence this caution not to expose the
plates unnecessarily.
(See _Church_: "The Chemistry of Paints and Painting," third edition,
pages 257-263.)
_Plate I_