Taw′ing.
A process of tanning in which mineral agents are substituted for vegetable extracts.
The leather produced is known as
Hungarian, white, or
alum leather; the latter from the use of alum as the principal agent.
Tawing was practiced by the Romans.
We read in Isidore of
calcei (shoes), called
alutoe, because the skin was softened by alum.
 |
|
Tatting-shuttle winder. |
The skins usually subjected to this process are those of the goat, sheep, deer, dog, and some other skins of small size, such as the raccoon, ground hog (woodchuck), fox, etc., some of which are tanned as pelts, retaining the hair.
The preliminaries depend upon the purpose for which the skin or pelt is intended; if it be unhaired, the process is accomplished by liming.
The skin is then carefully washed and rubbed to remove the lime.
The skins are then steeped in a fermenting bran mixture, whose proportions are two pounds of bran to the gallon of water.
This develops acetic acid, which neutralizes the lime and swells the skin.
The time of steeping is from three days to as many weeks, according to the temperature.
The sinking of the skins in the menstruum is the evidence of the completion of the process.
The skins are then steeped in the alum bath, which is thus prepared for 100 sheep-skins: —
| Alum | 20 pounds |
| Salt | 4 1/2 pounds |
dissolved in hot water, and diluted so as to saturate the skins.
The skins are tramped in the bath, or subjected to the tumbling operation in a closed revolving cylinder with interior slats.
[
2501]
The skins are then put into a paste made by adding to the alum bath
| Wheaten flour | 20 pounds |
| Yolks of | 50 eggs |
well mixed.
The skins are separately treated with this compound, and then left in it for a night.
They are then drawn, suspended on poles, and left to dry, being occasionally stretched.
They are then worked on the softening iron to remove unevenness, develop whiteness, and stretch uniformly.
The process is completed by stretching on hooks, rubbing with the stretching-iron occasionally, as the drying proceeds.
The skins may be surfaced with pumice, and glossed with a smoothing-iron.
When the
pelt is to be dyed, the wool or hair is colored previous to the alum bath.
The coloring of the
skin is by a tinctorial mixture applied to the grain side while damp, and rubbed in by an iron.
Split horse-hides are made into
tawed, white, or
alum leather, and are the material for leather aprons used by the mechanics of various arts, the pioneers of the army in full dress, for thongs of whips, and for other purposes.
In
Hungary and other countries of
Europe, alum-tanned leather, said to be equal to bark-tanned, is used to a considerable extent for harness.
The process, it is said, may be completed in 24 hours. Heavy ox or cow hides fresh from the slaughter-house are first well washed in salt and water to remove the blood, and then laid on the beam, flesh side up, and well scraped.
The hide is then placed on a smaller beam, and the hair removed with a sharp knife, after which it is placed in a tanning solution of salt and alum pulverized; the hide is well sprinkled with this and rolled up, and, as the liquid oozes out, it is heated and poured over the hide; this process is continued for 24 hours, when the leather is ready to take the grease; using a cold solution produces a firmer and less porous leather, but takes more time, — three or four days, — small quantities of alum being added to the solution each day. After scraping, the leather is colored with logwood and a small proportion of copperas; it is then rubbed with iron-black and dried.
It is finally well rubbed in the direction of its length, and smeared with a mixture of equal parts of hog's lard, tallow, and
train oil on the flesh side, tallow only being used on the grain side.
