A Text-book of Tanning: A treatise on the conversion of skins into leather, both practical and theoretical.Procter, H. R. (Henry Richardson)
Science
A Text-book of Tanning: A treatise on the conversion of skins into leather, both practical and theoretical.
Procter, H. R. (Henry Richardson)
Tanning
The dyeing of glove-kids is done in 2 ways:--_a._ The skins are plunged
into the dye-bath (_Tunkfarben_). In this way, all light colours are
ordinarily produced, such as _gris-perle_ (pearl-grey), _paillé_
(straw-yellow), _chamois_ (reddish yellow), silver-grey, aquamarine,
&c. _b._ The skins are spread on an inclined or rounded table of stone
or metal, and brushed over, on the grain side, first with a mordant
(_Beize_), then with the dye-liquor, and lastly, with a solution of
a mineral salt (Plate 7). The mordant serves to fix the colour on
the surface of the skin, to prevent its striking through, to produce
certain modifications of colour, and to enable any parts of the skin
which yet contain fat to take the colour evenly with the rest. To
satisfy these conditions, the composition of the mordants is very
varied. Potash bichromate, ammonia, potash, soda, and stale urine are
among the most frequently employed, seldom separately, but usually in a
mixture containing 2 or more.
Dye-stuffs of vegetable origin have always held the first place. Those
most in use are logwood (_Blauholz_), Brazilwood (_Rothholz_), the two
fustics--_Cuba Gelbholz_ (_Morus tinctoria_) and _Ungarisches Gelbholz_
(_Rhus cotinus_), several species of willow-bark and of berries,
indigo-carmine, and indigo dissolved in sulphuric acid.
Aniline colours used alone remained in fashion for a short time only,
but are now usefully employed as top-colours (_Ueberfarben_), viz.
brushed in very dilute solution over vegetable colours. In this way,
particularly tasteful shades of green, violet, and marine-blue may be
produced.
After the mordant has been applied once or twice, and the colour
3-6 times, a wash (_Ueberstrich_) containing some metallic salt is
generally applied, with the object either of bringing out the special
tone required, or of making the colour more lively and permanent.
The so-called "vitriols" are mostly employed: "white vitriol" (zinc
sulphate), "blue vitriol" (copper sulphate), "green vitriol" (iron
sulphate), and occasionally other salts.
Before dyeing, the greater part of the flour, salt, and alum must
be removed from the skins by washing with tepid water; and they
therefore require a second feeding (_Nahrung_) of egg-yolk and salt.
In the case of the skins which are dyed by plunging into the dye-vat
(_Tunkfarben_), this is done after the dyeing is completed; in that of
brush-dyeing, before the dyeing process.
After the dyeing, the skins, if dipped, are wrung out; if brush-dyed,
sleeked out with a brass plate, to get rid of superfluous water. They
are then dried in an airy room. Before staking (stretching), the skins
are laid or hung in a damp cellar, or in moist saw-dust. They are
staked twice: once damp, and once nearly dry.
Public-domain text, read in full here on John Shaqi.
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