AN IMPROVED COATING FOR PAPER AND OTHER MATERIALS DESIGNED TO RECEIVE LEAD PENCIL MARKS, WHICH MAY BE REPEATEDLY EXPUNGED WITH MOISTURE
Year: 1866

page_text: PROVISIONAL SPECIFICATION left by Sylvester Franklin Schoonmaker
at the Office of the Commissioners of Patents, with his Petition,
on the 24th December 1866.
I, SYLVESTER FRANKLIN SCHOONMAKER, of New York City, United States of
America, now of Euston Square, in the County of Middlesex, Chemist, do
hereby declare the nature of the said Invention for "AN IMPROVED COATING
FOR PAPER AND OTHER MATERIALS DESIGNED TO RECEIVE LEAD PENCIL MARKS,
WHICH MAY BE REPEATEDLY EXPUNGED WITH MOISTURE," to be as follows:-
.!
The said Invention relates, more particularly to a coating for paper and
other materials,, which is composed of a resin having incorporated with it a
white, soft, and non-gritty material, by means of which the resinous coating is
rendered capable of receiving distinctly the marks of a lead pencil.
It is well known that resinous solutions when applied over any surface will
harden with such a complete union of the particles as to present a glassy
and lustrous coating, which will not readily receive marks of lead pencil.
Various attempts more or less successful have been made to overcome this
difficulty by incorporating with varnish certain materials essentially of a gritty
nature, whose particles are sufficiently harsh to abrade the lead of a pencil.
This method, however, is to a certain extent imperfect, as, though the required
abrasion of the lead of the pencil is effected, a corresponding effect is pro-
duced upon the varnish by the action of the pencil upon the gritty particles
incorporated with the said varnish, which is thereby soon completely worn
tbrough.

page_text: The resins or "gum resins" which form the principal component part of
the said varnishes are sufficiently hard in themselves to freely abrade the lead
of a pencil if the glassiness of surface due to the close union of the particles
of the said resins can be prevented.
To accomplish the last-mentioned object and to avoid the disadvantages
attending the use of a gritty substance for that purpose, china clay or tris-nitrate
of bismuth are employed in the form of an impalpable powder which is
incorporated in the proportions, herein-after stated, with the gum resin in
solution before its application to the paper, or afterwards by distributing it
evenly over the coated surface before the solution has hardened by drying.
Other soft and white material, as, for example, the substance known in
commerce as terra alba or terre blanc, may be successfully employed in the
same proportions as are stated for the china clay. The said china clay or.
other material employed must be carefully separated by flotation or suspension
in water from all gritty particles which may accidentally be present.
The gum resins employed by preference are sandarach or bleached lac
dissolved in either methylated or pyroxylic spirit in the proportion of about
three and one quarter pounds of the resin to one gallon of the spirit. When
the resin is completely dissolved, thirteen and a half ounces of the finest china
clay are thoroughly incorporated with the solution, which is then ready for
application to the paper or other materials to be coated. The coating of the
said paper is by preference effected by dipping the same in a bath of the
solution, but other methods of applying the latter may be employed.
The proportions of the materials above stated may be varied to a certain
extent, and the solvents named may be replaced by others, but with less
advantage. When the tris-nitrate of bismuth is used as a substitute for the
china clay, its proportion to the resin must be considerably greater. The
different layers of the coating may contain either one or the other of these
ingredients.