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Raw hides meaning2/16/2024 ![]() retanning - additional tanning agents are added to impart properties.neutralisation - the pH of the leather is adjusted to a value between 4.5 and 6.5.shaving - the leather is thinned using a machine which cuts leather fibres off.splitting - the leather is split into one or more horizontal layers.sammying - 45-55%(m/m) water is squeezed out the leather.wetting back- semi-processed leather is rehydrated.Crusting may include the following operations: The culmination of the crusting sub-process is the drying and softening operations. The chemicals added during crusting have to be fixed in place. Often a coloring operation is included in the crusting sub-process. ( June 2014) ( Learn how and when to remove this template message)Ĭrusting is when the hide/skin is thinned, retanned and lubricated. Unsourced material may be challenged and removed. ![]() Please help improve this section by adding citations to reliable sources. The pH of the leather when chrome tanned would typically finish somewhere between 3.8 and 4.2. This basification process fixes the tanning material to the leather, and the more tanning material fixed, the higher the hydrothermal stability and increased shrinkage temperature resistance of the leather. Once an even degree of penetration is observed, the pH of the float is slowly raised in a process called basification. Regular checks will be made to see the penetration by cutting the cross section of a hide and observing the degree of penetration. The hides are allowed to soak (while the drum slowly rotates about its axle) and the tanning liquor slowly penetrates through the full substance of the hide. At this point the hides are loaded in a drum and immersed in a float containing the tanning liquor. The acidity (pH) of hides once they have finished pickling will typically be between 2.8 and 3.2. This product is commonly called “wet blue”. The most commonly used tanning material is chromium, which leaves the leather, once tanned, a pale blue colour. A large number of different tanning methods and materials can be used the choice is ultimately dependent on the end application of the leather. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that can putrefy when re-wetted ( wetted back), while tanned material dries out to a flexible form that does not become putrid when wetted back. Tanning is the process that converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. Main article: Tanning (leather) Barrel for leather tanning, Igualada Leather Museum, Spain depickling - raising of the pH out of the acidic region to assist with penetration of certain tanning agents.Pickling is normally done to help with the penetration of certain tanning agents, e.g., chromium (and other metals), aldehydic and some polymeric tanning agents pickling - lowering of the pH value to the acidic region.bleaching - chemical modification of dark pigments to yield a lighter coloured pelt.frizing - physical removal of the fat layer inside the skin.degreasing - natural fats/oils are stripped or as much as is possible from the hide/skin.bating - proteolytic proteins are introduced to the skin to remove further proteins and to assist with softening of the pelt.deliming - liming and unhairing chemicals are removed from the pelt. ![]()
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