AN IMPROVED METHOD OF DYEING LEATHER BLACK
Year: 1880

page_text: LETTERS PATENT to Niels Georg Sörensen, of Stockholm, in the Kingdom of
Sweden, for an Invention of "AN IMPROVED METHOD OF DYEING LEATHER
BLACK"
PROVISIONAL SPECIFICATION left by the said Niels Georg Sörensen at
the Office of the Commissioners of Patents on the 7th October 1880.
NIELS GEORG SÖRENSEN, of Stockholm, in the Kingdom of Sweden.
IMPROVED METHOD OF DYEING LEATHER BLACK."
<< AN
This Invention relates to an improved method of dyeing leather black, by means
of which such operation is effected in a more convenient, cleanly, effectual, and
durable manner than is the case when the ordinary methods are employed.
The leather to which the said method of dyeing applies is such as has been
tanned, that is to say, treated by or with tannic acid, or gallic acid, or any of those
derivations or combinations of or with such acids as turn black when acted on by
compounds or preparations of vanadium. The particular derivations or combi-
nations of the said acids on which the compounds or preparations of vanadium
have the desired effect, and also the nature of the said compounds or preparations
which it is desirable to employ, are known to chemists.
•
The dyeing can be effected at any time after the leather has been tanned, as
above referred to; the action of the vanadic compound or preparation, which is
employed in solution on the surface or body of the leather treated, is to turn it
black (the word black is not employed here in its strictly literal sense, but in its
ordinary acceptation).
It will be well understood that in order not to in any way injuriously affect the
quality of the leather it will be most advantageous to employ a neutral vanadic
solution, and I have successfully employed a neutral solution of vanadiate of
ammonia containing one per cent. of the latter salt.
In order to bring out a full black colour I have found that the moderate use and
application of heat is of beneficial influence.
The blackening of leather by vanadium compounds or preparations, as herein-
before described, is especially advantageous in the treatment of manufactured
articles, such as boots and shoes, as the risk of damaging the upper portions of the
same is avoided, and in the case of ornamental stitching in saddlery ware the
leather is rendered black whilst the said stitching retains its proper color, it also
allows the operation to be performed without soiling the hands of the operator;
another advantage is, that by the employment of vanadic compounds or preparations
the color can be made to penetrate deeper into the leather than is the case with
the ordinary dyes used.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Niels Georg Sörensen in the Great Seal Patent Office on the
7th April 1881.
"
NIELS GEORG SÖRENSEN, of Stockholm, in the Kingdom of Sweden. AN
IMPROVED METHOD OF DYEING LEATHER BLACK."
My said Invention relates to an improved method of dyeing leather black, by
means of which such operation is effected in a more convenient, cleanly, effectual,
and durable manner than is the case when the ordinary methods are employed.
The leather to which the said improved method of dyeing applies is such as has
been tanned, that is to say, treated by or with tannic acid or gallic acid in any
ordinary manner, so that it will contain such acids or any of these derivations or
combinations thereof as turn black when acted on by compounds or preparations of
vanadium. The compounds or preparations of vanadium which it is desirable to
employ for the purposes of this Invention are such as will not deteriorate the
quality of the leather treated, and I have found that a neutral solution of vanadate
of ammonia, or a solution of vanadic acid in water will effect the desired object in
a satisfactory manner.
The dyeing can be effected at any time after the leather has been tanned, even
after it has been oiled or greased. The leather is placed in the vanadic solution,
or impregnated with the same in any suitable way, by which means the black
colour is quickly developed; it is necessary to expose greased leather longer to the
action of the vanadic solution than leather not oiled or greased. The time during
which the leather should remain exposed to the action of the vanadic solution
depends upon the quality of the leather, and also upon the degree of concentration
of the vanadic solution employed; for instance, I have found that for the purpose
of dyeing finished leather goods, such as boots or saddlery ware, the desired object
is advantageously attained by moistening the surfaces of such leather goods with a
neutral solution containing one per cent. of vanadate of ammonia, the action of
which, in dyeing leather black, is very rapid; if treating greased leather, I immerse
it in a solution of one tenth of one per cent. of vanadic acid in water, to the action of
which I leave it exposed for several hours. For producing a full black colour I
find it advantageous to use moderate heat during the process of impregnating and
dyeing the leather.
Although in the above examples I have referred to certain proportions, I do not
confine myself to the same, as they can be varied without departing from the
principles of this Invention, as will be well understood.
The blackening of leather by vanadic compounds or preparations, as hereinbefore
described, is especially advantageous in the treatment of mauufactured articles,
such as boots and shoes, as the risk of damaging the upper portions of the same is
avoided, and in the case of ornamental stitching in saddlery ware the leather is
rendered black whilst the said stitching retains its proper color, it also allows the
operation to be performed without soiling the hands of the operator; another
advantage is, that by the employment of vanadic compounds or preparations, the
color can be made to penetrate deeper into the leather than is the case with the
ordinary dyes used.
Having thus described and ascertained the nature of my said Invention, and
the manner in which it is to be performed, I would observe in conclusion that what
I consider novel and original, and therefore claim as constituting the Invention
secured to me by the said hereinbefore in part recited Patent is,-
The method of imparting by the use of vanadic compounds or preparations a

page_text: black color to leather, containing tannic acid or gallic acid, or derivations or
combinations thereof, substantially as herein before set forth and described.
In witness whereof, I, the said Niels Georg Sörensen, have hereunto set my
hand and seal, this Thirty first day of March, in the year of our Lord One
thousand eight hundred and eighty one.
NIELS GEORG SÖRENSEN. (LS.)