AN IMPROVEMENT IN TINTING OR COLORING SPECTACLE AND OTHER LENSES
Year: 1872

page_text: LETTERS PATENT to Robert Thomas, of Shepherds' Bush, in the
County of Middlesex, for the Invention of "AN IMPROVEMENT IN
TINTING OR COLORING SPECTACLE AND OTHER LENSES."
Sealed the 26th July 1872, and dated the 22nd May 1872.
PROVISIONAL SPECIFICATION left by the said Robert Thomas at the
Office of the Commissioners of Patents, with his Petition, on the
22nd May 1872.
I, ROBERT THOMAS, of Shepherds' Bush, in the County of Middlesex,
5 do hereby declare the nature of the said Invention for "AN IMPROVE-
MENT IN TINTING OR COLORING SPECTACLE AND OTHER LENSES," to be as
follows:-
Hitherto ordinary colored lenses have been subject to the defect of
want of uniformity in the depth of tint, which necessarily increases in
O proportion to the thickness of the lens, owing to the greater body of
color at that part, the pigment being equally distributed through the
mass of glass of which the lens is composed.

page_text: bine two lenses, using in both cases uncolored glass, and unite the two
parts or lenses by means of an adhesive substance, with which a sufficient
proportion of the pigment has been previously mixed to impart the
desired tint to the lens. For this purpose Canada balsam colored as
required may be used, the aid of heat being employed to distribute it
equally between the parts, and expel air bubbles. It is necessary that
the surfaces to be united should correspond with truth to ensure an
equal distribution of the coloring matter whereby to obtain a perfectly
transparent and even tint of the same shade at all parts of the lens.
Lenses so colored may be applied to telescopes and other glasses as
well as to spectacles and eye glasses.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Robert Thomas in the Great Seal Patent Office on
the 17th September 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
THOMAS, of Shepherds' Bush, in the County of Middlesex, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-second day of May, in the year
of our Lord One thousand eight hundred and seventy-two, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Robert Thomas, Her special licence
that I, the said Robert Thomas, my executors, administrators, and assigns,
or such others as I, the said Robert Thomas, my executors, adminis-
trators, and assigns, should at any time agree with, and no others,
from time to time and at all times thereafter during the term therein
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "AN IMPROVEMENT IN TINTING OR
COLORING SPECTACLE AND OTHER LENSES," upon the condition (amongst others)
that I, the said Robert Thomas, my executors or administrators, by
an instrument in writing under my, or their, or one of their
hands and seals, should particularly describe and ascertain the nature
of the said Invention, and in what manner the same was to be

page_text: performed, anu cause the same to De red in the Great Seal Patent
Office within six calendar months next and immediately after the date
of the said Letters Patent.
NOW KNOW YE, that I, the said Robert Thomas, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement, reference being had to the accompanying Drawings,
and to the letters and figures marked thereon (that is to say): —
Spectacle lenses made of ordinary tinted glass have hitherto been
subject to the defect of inequality in the density of the tint, which in a
convex lens, for instance, is darker at the centre than at the edges
because the coloring pigment being contained in the substance of the
glass from which the lens is made, a greater body of color is necessarily
present where the lens is thickest. This defect it is the object of my
Invention to remedy.
According to my Invention I make the lens of two parts, or lenses of
uncolored glass, combined like those of an ordinary achromatic lens,
and united by means of a colored transparent cement, whereby the
desired tint is imparted to the lens.
This method, which I term "intertinting," I will now proceed to more
fully describe by the aid of the annexed Drawings, in which are shown
the different forms of lenses commonly in use.
Figure 1 is a cross section of a plano-convex lens composed of a
bi-convex lens a, and a plano-concave lens b, these lenses being precisely
similar to those of an achromatic lens, and united as hereafter described;
Figure 2 shows a bi-convex lens composed of two plano-convex lenses
and a bi-concave lens consisting of two plano-concave lenses united in
a similar manner; Figure 3 shows similar lenses composed of a bi-convex
or a bi-concave lens a and a meniscus lens b, similarly united.
In Figures 1 and 3 lenses a are preferably of crown glass, and lenses b
of flint glass, while in Figure 2 the lenses are made wholly of crown
glass.
I employ Canada balsam previously colored as required for uniting
the two lenses or parts of lenses. I prefer to employ Prussian blue as a
coloring matter, but any other transparent color desired may be used, the

page_text: pigment being rubbed down in a little turpentine, which is then mixed
with the balsam until the desired depth of tint is attained. The lenses
to be united are first heated on a plate to about 120 degrees Fahrenheit,
and when hot sufficient colored balsam is applied on one lens, and the
other lens then immediately applied thereon with a gliding motion and
slight pressure to expel the air and any excess of balsam, precisely as in
mounting transparent objects for the microscope. The complete lens is
then placed on a levelled stand and submitted to a uniform temperature
of about 95 degrees for about 2 hours in order to bake or harden the
balsam and perfect the union of the parts. It is necessary that the
surfaces to be united should correspond with truth to ensure an equal
distribution of the coloring matter. By this method of intertinting a
perfectly transparent and even tint of the same shade at all parts of the
lens may be obtained.
Lenses so colored may be applied to spectacles and eye glasses, and
also serve as the eye lenses of telescopes, opera and field glasses.
Having described the nature of my Invention, and in what manner
the same is to be performed, I would observe that I am aware that it
has been attempted to tint a certain kind of lens used by oculists by
interposing a thin layer of colored glass between two plano lenses, but
this renders the lens useless for the purposes to which the lenses of my
Invention are applied, and moreover such a method is quite distinct from
the method of my Invention; but what I claim as my Invention to be
protected by the herein-before in part recited Letters Patent is, making
tinted or colored lenses by uniting two colorless glasses or lenses by
means of a transparent colored cement or adhesive substance applied
between them, substantially as and for the purpose herein-before
specified.