IMPROVEMENTS IN THE DYEING OF COTTON WOOL (OR WASTE) BLACK AND BROWN
Year: 1860

page_text: LETTERS PATENT to David Dawson, of Milnes Bridge, near Huddersfield,
in the West Riding of the County of York, Dyer, for the Invention of
"IMPROVEMENTS IN THE DYEING OF COTTON WOOL (OR WASTE) BLACK
AND BROWN."
Sealed the 23rd October 1860, and dated the 23rd June 1860.
PROVISIONAL SPECIFICATION filed by tho said David Dawson at the
Office of the Commissioners of Patents with his Petition, on the 23rd
June 1860.
I, DAVID DAWSON, of Milnes Bridge, near Huddersfield, in the West
Riding of the County of York, Dyer, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN THE DYEING OF COTTON WOOL (OR WASTE)
BLACK AND BROWN," to be as follows:-
In order that my improvements in dyeing cotton wool or waste black
and brown, may be perfectly understood, I will describe the old methods
of dyeing these two colors as ordinarily practised. There are two ways
practised for dyeing black, one technically called "sumach way," and the
other "chrome way." For dyeing black the "sumach way," the process
is as follows: First, the cotton is steeped in a decoction of sumach,
the strength of which is proportionate to the depth of color to be dyed.
-

page_text: Generally, however, about fifty pounds of sumach to each hundred pounds of
wool will suffice. After remaining in this, say, about twelve hours, it is taken
out, well drained, and then wrought in a saturated solution of lime. Here
the tannic or gallic acids from the sumach combine with the lime, and form
an insoluble compound within the fibre; it is then taken out of this lime bath,
or more generally the spent lime water is let out by an egress at the bottom
of the vessel.
If the cotton be allowed to remain in this state exposed to the atmosphere
considerable detriment will be done, as the tannate or gallate of lime rapidly
attracts oxygen, and if allowed to remain till the absorption of oxygen is com-
pleted, it no longer yields a black compound when wrought in a solution of
sulphate of protoxide of iron. The cotton must then be immersed in the next
bath, which is made up with sulphate of protoxide of iron immediately when
taken out of the lime bath. There a double decomposition ensues, tannate
and gallate of protoxide of iron and sulphate of lime being formed.
The next process is to destroy the superfluous sulphate of protoxide of iron
which invariably adheres to the cotton when removed from that solution. To
effect this it is wrought through a solution of lime; this being done the
cotton wool is effectually mordanted and ready for dyeing in a decoction of
logwood a deep black.
The other method, or "chrome" method, I will now describe. A solution of
catechu is made by boiling about forty pounds of catechu to each hundred pounds
of wool intended to be dyed, and an 8th part of the weight of catechu used of
sulphate of copper is added. The wool is steeped in this about twelve hours,
it is then, after well draining from the solution of catechu, wrought in a solution
of bichromate of pottassa at boiling heat. It is more than probable that in
this process the chrome acid is reduced to the state of sesquoxide of chromium,
and this oxide forming insoluble compounds with the organic acids of the
catechu. However, cotton wool mordanted in this manner, though effectual
in saturating the organic acids of the catechu, is nevertherless only capable of
taking on a wan or pale color.
The wool is, when removed from the chromate solution, washed in cold
water in order to rid it of the superfluous soluble chromate which always
adheres to the wool when the bichromate of potassa has been used in excess.
and in order to ensure complete saturation it is necessary to use it in excess.
The wool is now mordanted and ready for dyeing in a decoction of logwood.
My process is founded upon the weak basic properties of sesquoxide of iron,
and its liability to separate from its dilute solutions. I steep the cotton wool
in a solution of catechu made exactly as for the chrome black. then I work

page_text: the cotton through a cold dilute solution of sesquoxide of iron. By this means
I can get a perfect saturation of the organic acids of the catechu with the
sesquoxide of iron, which is a far superior mordant to the sesquoxide of
chromium for black; I then destroy the superfluous salt of sesquoxide of iron
which always remains attached to the cotton when removed from a solution of
that salt, by working the cotton through a solution of lime. The cotton is
then ready for dyeing a full deep black with a decoction of logwood, or a good
red brown with the coloring matters of sandalwood, barwood, or camwood.
This process may be used, no matter what the cotton wool may have been
steeped in, whether "sumach," "catechu," "morablaus," "divi divi," or any
other substance containing gallic or tannic acids.
The process will also be most advantageous for cotton skein dyeing.