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The history of Basic Chrome Sulfate as a tanning agent for Leather
Leather has been always very important for mankind, for two reasons: one, cattle rising is of great importance and generates enormous amounts of skins that must be handled; second, tanned cattle skins become beautiful and soft leather, a material very appreciated in everyday life.
Tanning has been a very traditional craft done in several ways. After the dawn of the industrial revolution, the demand for softer leather rose dramatically and a very efficient tanning agent was developed to respond to this need: Basic Chrome Sulfate. Chrome tanning, in the 1800's, enabled a shorter time in the entire process. Chrome forms complex chelates with conditioned raw skin, which in this way becomes durable, strong, and soft leather, able to stand all kinds of practical situations.
The tanning process involves several stages, as follows: preparation of the skin for tanning; actual tanning and other chemical treatment; retanning, in which retanning agents and dyes are applied to the material to provide physical strength and desired properties and finishing, in which finishing materials are applied to the surface or in other cases, the surface is physically polished and finished.
Before the Chrome tanning process, the hides and skins are treated with a mixture of salt and sulfuric acid to lower the pH of the skin collagens and so facilitate the penetration of the tanning agent into the substance. This process is called pickling. After pickling, the tanning Chrome salt is added in a bath with the conditioned skins until a desired penetration of Chrome into the substance is achieved. The pH of the material is then being raised again, in the so called basification, which helps fixing the chrome in the skin, which gets a blue color and referred to as "wet blue." Chrome tanning is faster than vegetable tanning and produces stretchable leather which is excellent for use in handbags and garments.