CURING
For transport (from source to tannery) purposes, simple methods of stopping putrefaction arose. Drying is the most obvious method. Dry skin does not putrefy and can be soaked in water to return to the raw condition. Wet-salting, dry-salting, (or pickling with acid and salt) are other methods of preservation.
Wet-salting: the cold, flayed hide is spread out, flesh side up, on a concrete floor and wellsprinkled with salt (coarse grained salt spreads better). A second hide is placed on top and also sprinkled with salt. The salt dissolves in the moisture in the skin and the brine permeates the pile. Amount of salt (clean) used 25-30 % of raw hide weight.
Marine salt bacteria give rise to red or colored patches on the flesh. Their action can be stopped by mixing soda ash and napthalene with salt (for 44kg salt, 0.5kg napthalene and 1kg of soda ash is used).
Brining: more efficient. Hides are cleaned and hung in large paddles in a very strong salt solution(14kg salt to 45.5kg of cold water). Uniform salt penetration in 12-14 hours. Hides are then drained and piled. Both brining and wet salting require large quantities of salt and the cured hide is still damp (50 % water).
Dry-salting: the flayed skin is salted by either or both of the above methods and then hung up to dry. This reduces weight and cost of transport.
Drying: Activity of bacteria ceases when hide contains 10-14 % moisture.
important: drying should be gradual and even(parts getting too hot may gelatinize and dissolve away when put in water).
Ground dried- disadvantages: poor ventilaton on the ground side, high temperature on exposed side.
Sun-dried when laid or hung on poles or ropes, better ventilation and quicker drying but heat damage and rope marks may result.
Frame dried- if put too tightly weakness and thinness may be caused.
Shade dried- dried open sided, covered shed, off the sun and well ventilated.
Dried hides require careful packing. Must not be bent or creased (cause cracks). Dried hides are open to insect attack. Insectisides used for prevention. Anthrax (sirpence) may be present on dry hides. May be fatal for workers that may be infected (destroys red blood cells). No danger after liming.
Pickling: Always used for hides after unhairing, liming and fleshing.
After unhairing, liming and deliming the skins are washed and then paddled or gently drummed in a 12 % salt solution (5.5kg per 45kg of cold water ~12%) 10 to 21 degrees C- to which 1 % or 1.2 % of sulphuric acid is added. Continued for 2 or more hours. Salt and acidity of the liquor should be checked to ensure salt concentration is still more than 10 % and acid concentration is still above 0.8 %.
May now be stored for several months (at above 320C, acidity may cause damage to skin).
All known putrefying bacteria stops activity at pH 2.0, but not mould growth.
Fungisides (at 1/1000 parts of liquor) used: ie. sodium trichlorophenate, sodium pentachlorophenate, beta-napthol, p-nitrophenol (may give yellow color).
Pickled skin should not be allowed to dry (acids or crystals may cause damage).
