The Manufacture of Upholstery Leather

Curing - As soon as the hide has been removed from the animal it must be protected from putrefactive bacteria. Curing is a method of short term preservation. This is achieved by either sprinkling it liberally on both sides with common salt, or by immersing it in a saturated brine solution.

Soaking - On arrival at the tannery the hides are soaked in water to remove the curing salt. This is most generally done in revolving processors holding anything from 100 to 200 hides in a load.

Liming - The hair and epidermis are removed by treating the hides in a solution of lime (calcium hydroxide) and sodium sulphide. The hide also swells up in this process, which gives the finished leather the required softness and flexibility required for upholstery purposes. This process lasts one to two days.

Tanning - Tanning involves combining the tanning agent and the hide protein to form a stable, durable, non-putrescible leather. After liming and fleshing (the removal of fat adhering to the back of the hide) the hide is split layerwise to produce a fine, smooth grain leather after tanning. The hides are then delimed to remove all the alkalies from the liming process, this is followed by a weak enzymatic treatment called bating. This last named treatment makes the grain finer and smoother and gives the correct elasticity and plasticity in the finished leather. The final treatment before tanning makes the hide weakly acidic and is achieved either by pickling the hides in a weak acid and salt solution, or by a suitable pre-tanning process. The tanning process are of two main types, vegetable tanning and mineral tanning.

Vegetable Tanning - In this case the hide is treated with vegetable tannins found in the bark and wood of certain trees. For centuries the bark of the oak tree was used as a source of tannin, but today a more common tannin is mimosa tannin found in the bark of various species of wattle tree. Traditionally the vegetable tanning is done in pits, the hides are suspended in a series of pits or vats of tannin solution which gets progressively stronger. This process is slow and may take several weeks, or even months, before the hides are fully tanned. This method is now rarely used in the production of upholstery leather. More modern scientifically controlled processes are carried out, using drums in the later stages of the process, to accelerate the process.

Mineral Tanning - This tannage is commonly carried out with the aid of basic chromium sulphate, a mineral salt which penetrates the hide very rapidly, tanning being complete in twenty-four hours. The leather is a pale duck-egg blue in colour, and after suitable processing yields fine soft modern leather. Other mineral tannages (eg Aluminum Sulphate) are also used. Retanning - Hides are now in the finishing stage of production. A wet drum process allows the addition of dyes, anti-mould chemicals, a re-tan agent, fat licquors to give the finished product a soft feel, and where necessary, flameproof chemicals.
Drying - Hides are dried by first of all wringing excess water out in a large mangle, or setting machine, and then by stretching the hides on a frame which is then passed through a lagre heating chamber.

Pigmentation and Lacquering - Finished hides will have pigments applied to the surface. This is done using a combination or a roller coated for the initial application, and a spray carousel to add subsequent coats of pigment. A top lacquer coat is applied to give the finish a layer of protection against wear and soiling.

Embossing - An embossed grain pattern is sometimes "printed" onto the leather's surface. This creates a more uniform break (the natural pattern which occurs along the folds of the hide) and will help to disguise scars and marks.

Drumming - The hides are placed in side large stainless steel drums and tumbled. During this process the natural fibres start to loosen and a soft feel (or handle) is created.

Inspection - Andrew Muirhead has a 100% inspection policy where we make final checks for colour accuracy, thickness and general appearance of the hides. This is carried out on our inspection table and in our testing laboratory. For more information on our testing, click here.

Packing - Hides are distributed from our factory in bales of up to 10 hides. Packing lists and full customer order details accompany the hides. We offer a next day service for goods despatched from our warehouse facility.