AN IMPROVED PIGMENT
Year: 1882

page_text: LETTERS PATENT to Joseph Benjamin Freeman of White Hart Lane, Tottenham
in the County of Middlesex, Varnish and Color Manufacturer for an Invention
of AN IMPROVED PIGMENT
PROVISIONAL SPECIFICATION left by the said Joseph Benjamin Freeman
at the Office of the Commissioners of Patents on the 13th October 1882.
JOSEPH BENJAMIN FREEMAN of White Hart Lane Tottenham in the County
of Middlesex, Varnish and Color Manufacturer, 'AN IMPROVED PIGMENT."
"
This Invention relates to an improved white pigment composed of sulphate of
lead and oxide of zino or zinc white and magnesia prepared in the following
manner I produce sulphate of lead by dissolving litharge in acetic acid and
precipitating by sulphuric acid, or in any other manner, which is then washed and
dried. In this state it is quite useless as a pigment, lacking density and opacity,
but by adding a suitable proportion of oxide of zinc or zinc white and submitting
the mixture to great pressure and friction by grinding under ordinary edge runners
or otherwise when either dry or wet, the particles of the zinc and lead mix in a
remarkable manner, producing an entire change in their character. I add about
2 per cent of magnesia or carbonate of magnesia and grind this with the other
materials. The product when ground with oil in the customary way, furnishes
a pigment having great body and opacity quite equal to the finest white lead
produced by the Dutch method, while it is superior to it in color and possesses
little or no smell.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Joseph Benjamin Freeman in the Great Seal Patent Office on
the 13th April 1883.
JOSEPH BENJAMIN FREEMAN of White Hart Lane, Tottenham in the County
of Middlesex. Varnish and color Manufacturer. AN IMPROVED PIGMENT
This Invention relates to an improved white pigment composed of sulphate of
lead and oxide of zinc, or zinc white (and in some cases carbonate of magnesia) the
pigment being prepared in the following manner :-
produce sulphate of lead (by dissolving litharge in acetic acid and precipitating
by sulphuric acid, or in any other manner) which is then washed and dried. In
this state it is quite useless as a pigment, lacking density and opacity, but by
adding a suitable proportion of oxide of zinc, or zinc white, and submitting the
mixture to great pressure and friction by grinding (preferably when dry) under
ordinary edge runners or otherwise, the particles of the zinc and lead become
incorporated together in a remarkable manner, producing an entire change in their
character.
The zinc white may be added to the sulphate of lead when the latter is in a wet
state, and the mixture then dried and ground as above mentioned.
The product when ground with oil in the customary way forms a paint having
great body and opacity quite equal to white lead produced by the Dutch method,
while it is superior to it in color, durability, and density, and possesses little or no
Bmell.
I find that 1 part by weight of oxide of zinc or zinc white, to 3 parts by weight
of sulphate of lead answers well, but these proportions may be varied, and I do
not limit myself in this respect, as a greater proportion of either ingredient may
be used.
When found necessary-for instance when a larger proportion of zinc oxide is
used a small amount of carbonate of magnesia, (about 2 per cent) may be added
to the mixture with a view to render the combination of the oil with the zinc
oxide more complete. The carbonate of magnesia would by preference be added to
the sulphate of lead and zinc oxide while the mixture is being ground either under
the edge runners or otherwise.
Having described the nature of my Invention and the manner of performing the
same, I declare that what I claim as my Invention to be protected by the herein
before in part recited Letters Patent is.
The manufacture of a white pigment by mixing together lead sulphate and zinc
oxide or zinc white, (with or without the addition of carbonate of magnesia) and
submitting the mixture to great pressure and friction, substantially in the manner
herein specified.
In Witness whereof I the said Joseph Benjamin Freeman have hereunto set
my hand and seal this thirteenth day of April. A.D. 1883.