A Process of Imparting a Permanent Coloring to Turquoises and other Precious Stones.
Year: 1891

page_text: Date of Application, 25th Aug., 1891-Accepted, 26th Sept. 1891
COMPLETE SPECIFICATION.
A Process of Imparting a Permanent Coloring to Turquoises and
other Precious Stones.
A communication from AUGUST KÜHNE, of 31, Striessener Strasse, Dresden, in
the Empire of Germany, Schoolmaster.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
M.I.M.E., do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement :-
It is often found that turquoises and other similar precious stones are defective
in coloring and show at some parts spots of a different hue to the other parts.
In the case of turquoises for instance these spots have generally a greenish hue.
It has also been observed that in course of time turquoises are apt to lose their
original blue color and to "bleach" i.e. become pale or assume a greenish hue.
The object of this invention is to remedy these defects by first removing that
which in the primitive coloring of the stone is apt to change or disappear, thereby
altering the chemical condition thereof and then permanently coloring the stone by
means of aniline whereby a turquoise for example will acquire a beautiful uniform
blue color not only covering its surface but penetrating its substance so as to enable
the stone to be subsequently ground or cut.
In the first stage the stones are immersed in a solution of tartaric acid and water
(20 grammes of acid in one litre of water). Considering however that the coloring
substance of turquoises and like stones mainly consists of combinations of copper
or iron the dissolving process of such coloring substance may be commenced by
using, instead of tartaric acid, a mixture of such acid with sulphate of copper or
iron (say 40 grammes of sulphate and 10 grammes of tartaric acid dissolved in
one litre of water). The solution containing the stones is heated up to the
point of ebullition, when the stones are removed and placed into an alcohol bath
into which are gradually introduced the aniline colors mixed with a little water.
In this bath the stones are left for 24 hours after which the coloring material
contained in the solution will have sufficiently permeated the stones to color them
not only on the surface but a certain distance inwardly so that they may be cut or
ground without losing any of the uniformity of their coloring.
Having now particularly described and ascertained the nature of the said inven-
tion as communicated to me by my foreign correspondent and in what manner
the same is to be performed, I declare that what I claim is :-
A process for coloring turquoises and other precious stones by means of aniline
colors the stones being first purified or decolorized in a bath consisting of a
solution of tartaric acid or of a mixture thereof with sulphate of copper or iron
and then colored in an alcohol bath to which the required aniline color dissolved
in water is gradually added.
Dated this 25th day of August 1891
W. P. THOMPSON & BOULT,
Agents for the Applicant.