Improvements in or relating to the Tanning of Hides or Skins.
Year: 1895

page_text: Date of Application, 1st Apr., 1895-Accepted, 11th May, 1895
COMPLETE SPECIFICATION.
Improvements in or relating to the Tanning of Hides or Skins.
We, FRANCESCO PRELLI, of Via Bouzanigo 43, Turin, Italy, Tanner, and
BARTOLOMEO DEMO, of Via del Mercato 42, Turin, Italy, Tanner, 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:-
This invention has for object to reduce the time and cost heretofore usually
required for tanning hides or skins (hereinafter called hides).
For this purpose, after the hides have been subjected to the usual preparatory
processes for removal of the hair and flesh, and for cleansing them, we subject them
whilst agitated, to the action of a strong extract of tannin such as is obtained in
commerce in the form of a syrup of about 20° 25°, or 30° Beaume, the proportion
of the extract of tannin used, being varied according to the percentage of tannin
present therein.
In carrying out the invention the hides and the tannin are placed in a drum
or other vessel which is then revolved, oscillated or otherwise operated or a
stationary vessel provided with an agitating device, the arrangement in either
case being such as to subject the contents of the drum or vessel to violent agitation.
The speed of revolution or oscillation may vary, but the most suitable speed when
à drum is used, is from about 12 to 20 revolutions per minute.
The absorption of the tannin by the hides is very rapid, under the action of
the rotary motion, especially at the beginning of the operation. No disadvantage
results from the richness of the tanning liquor diminishing as the process proceeds.
It should however be noted that the heat produced during the process, is useful
only up to a certain degree, say up to about 40° Centigrade. If the heat should
rise beyond this limit, it is liable to damage the hides, and in such a case the
drum or vessel must be stopped and opened to allow the temperature to fall;
or if the heat is very great, the hides should be taken out, which will do them
no harm.
By this method, the tanning of hides is effected in from 3 to 30 hours according
to the thickness of the hides. As the method is based essentially on the simul-
taneous use of a highly concentrated solution of tannin and of violent motion in
an apparatus of suitable construction, such as herein before referred to, it is not
necessary that the hides should be subjected to special processes for swelling the
same, and for removing the grease therefrom. Nor is it essential to add substances
such as sulphuric acid or turpentine to the extract of tannin.
To ascertain when the tanning process is completed, the hide treated can be cut
in the thickest part; it can then be seen whether the tannin has properly entered
the pores therein, and whether the proportion of tannin used to the weight of the
hides being treated, has been correctly calculated. When the hides are completely
tanned, the tannin should have been almost entirely absorbed, leaving merely an
almost exhausted liquor behind.
Although by means of the method described, hides can be properly tanned without
the addition of other substances to the tanuin, we have obtained the best results by
adding to the tannin an emollient such as an oil, fat, solution of soap, fatty mucilage
or other fatty body. The emollient protects the hide from a too energetic action
of the tannin, and it softens the grain of the hide, and improves the quality thereof.
On the selection and amount (which is always small) of the said substance, depends

page_text: the applicability of the hides for the operations which the latter are intended to
undergo subsequently. For the tanning of hard skins to be used for soles, a less
quantity of emollient is necessary, whilst for. supple skins a greater quantity is
necessary. The choice of the emollient depends on the quality of the skin that it
is desired to tan-e.g. for tanning skins for soles, there are preferably employed
emollients that are less fatty, and for supple skins more fatty emollients are by
preference employed.
The particular feature which distinguishes our method from other methods of
rapid tanning heretofore proposed, consists in the use of the tannin in a dense and
syrupy condition without the necessity of maintaining the percentage thereof
during the process in which the hides absorb the tannin gradually, leaving behind
merely a spent liquor which we have found to be of no value, the small number of
degrees it still shows being due rather to the substances rejected by the hides,
than to tanning principles.
The amount of tannin required may if desired, be introduced in two or more
stages, allowing the hides to absorb one lot before adding a second.
: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The herein described method of rapidly tanning hides by subjecting the hides
to the action of an extract of tannin of very great strength, and particularly such as
is found in commerce of about 20°, 25°, or 30° Beaume, the hides being simul-.
taneously agitated in a vessel, such as a revolving or oscillating drum, or in a
stationary apparatus provided with an agitating device, in such a manner that all
parts of them are subjected to the action of the taunin, as set forth.
2. In carrying out the method of tanning specified in the preceding claim, the
addition of an emollient substance such as an oil, fat, solution of soap, fatty
mucilage, or other fatty body to the extract of tannin for the purpose specified.
3. In the method of tanning specified in Claim 1, the gradual using up of the
tauuin of the tanning liquid without the addition of fresh tannin to maintain the
strength of the said liquid as set forth.
Dated this 1st day of April 1895.
Dated this 1st day of April 1895.
For the Applicants,
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.