about leather
Leather has been prized for centuries for its durability, softness and form fitting nature. Even as fabrics displaced hides as the primary means of covering the skin, leather has retained immense popularity for use in jackets, saddles, shoes, hats and numerous accessories. Formally, leather is any tanned hide of an animal, regardless of species, though most leather is made from cattle (bos primigenius). Animals such as deer, pigs, goats, alligators and even ostriches are also used. Animals which have a similar biological makeup, such as deer, will tend to produce leathers which are quite similar to those from cattle.
Deerskin, for example, looks and feels quite like bos primigenius leather, though afficianados would certainly know the difference. Essentially any animal skin can be used. As a general rule hides from younger, unscarred animals will generally be used in higher grades of leather, while older and more blemished examples will be used for lower grades.
The process of transforming the raw hide of the animal into a usable product is called tanning.
In ancient times, tanning was considered a noxious trade, which is not surprising when one considers the techniques used. Raw hides were soaked in urine or left to putrefy before dipping into a salt solution. After scraping off the hair, tanners would pound dung into the skin, or worse, mix dung and water in a vat and knead it with their bare feet. We shouldn't be surprised that tanneries were relegated to the outskirts of town!
Times have changed. The modern tanning process is highly automated and now uses neither urine nor dung!
If you are interested in a professional Vermont house cleaning service please go to our contact page and let us know. Nancy will be happy to discuss with you the details of your cleaning project.
The first step is curing. At this stage excess moisture is removed and the hides are suffused with salt either through brine curing or by salt packing. Subsequently the salt is removed by soaking the hides in clear water.
Next is the process of liming. Hides are soaked in a solution of quicklime (calcium oxide) or other disulfide reducing agent like cyanide or an amine. The goal is to reduce the fat content as well as to remove hair and keratin. Any hair left after the liming phase is removed physically, first through a mechanical process and then manually to ensure a clean hide. A further pre-tanning process called "bating" may also be done depending on the type of leather.
At this stage the hides are ready for the true tanning process. Tanning is required to strengthen the collagen in the hide to make it more durable and resistant to decay.
There are two essential types of tanning: Vegetable and mineral.
Vegetable tanning uses a substance which occurs naturally in many species of tree bark called tannin (hence the name "tanning"). This is a slow process, requiring the skins be stretched for weeks in tannin solutions. Vegetable tanning is used largely for leathers which need to be tough and durable, such as for soles, belts and watch straps.
Mineral tanning typically uses chromium sulfate for processing (though some other methods such as tara-aluminum tanning are occasionally used). The method is ideal for items which need to be soft and supple such as jackets, handbags and wallets. Because this requires a low-pH skin to facilitate penetration of the chromium, the hides are pre-treated in a solution of salt and acid. Once the chrome has suffused the skin adequately, the process of basification is started. This raises the pH to more neutral levels. Mineral tanning is much faster than vegetable tanning. Processing time is measured in hours rather than days.
Synthetic tannins (called "syntans" for short) have attained widespread use. Whitish when finished, these compounds are similar to vegetable tans only they are derived through chemical synthesis rather than by processing organic materials like tree bark. Initially these were seen as poor substitutes for true vegetable tannins, however improvements in the process have meant they have become fully accepted in the tanning industry, especially for "retanning" before the finishing phase.
Once the tanning process is done the leather is piled down, wrung and split. Splitting separates the flesh from the grain layers. The grain layer is that which faces the outside of the animal and is used for smooth grain finishes. The flesh layer is on the inside and is eventually processed to produce suede.
The processes at this point diverge depending on the type of tanning. In the case of vegetable tanned leather, the skins have to be suffused with moisture, colloquially known as "horsing up", then allowed to dry for one to two weeks in a cool enclosure.
Retanning is usually used in mineral tanned leathers to stabilize the tanning agent. This prevents leaching and, in the case of chromium tanning, removes the characteristic blue color. In fact the retanning agent is often some combination of vegetable tannins and/or syntans. Since the syntans have a bleaching effect, these are commonly used for white or pastel shades of leather.
After retanning, many leathers are dyed to achieve a desired color. This is as much of an art as a science because of the differences in pigmentation of the retanned leather. To achieve a desired end color, adjustments may be needed on the basis of the pigmentation of the ingoing leather sheets.
During fatliquoring leather is strengthened and moisturized by using various "sponging" compounds. Which sponging compounds are used vary greatly depending on the desired qualities of the finished product. Glycerine, soaps, animal oils, epsom salt, bicarbonates, mineral oil, egg yolk among other substances may be used. Recently steps have been taken to reuse the natural fats removed in the preparation phase for use later in fatliquoring, helping to reduce cost and waste in production.
After fatliquoring, the leather goes through a process of "setting out". This compresses and smooths the leather. Finally, the product is dried to bring moisture levels down to normal, equilibrium levels.
There are a variety of finishes available for leather.
Analine finishes use analine as a dye. This is intended to have a natural look. Such finishes require consistent sections of high quality leather because any grain faults will be clearly visible. Calf leather is often finished in this way as it tends to be free of blemishes and is well suited to the soft, "non-invasive" technique. Aside from showing any faults in the leather, analine finishes require special care from the user since it retains a fair degree of porosity, and is susceptible to staining and water damage.
Pull up aniline uses a top treatment of oil and sometimes wax. Though these do offer somewhat better resistance to moisture, the finish may be compromised through rubbing and scuffing.
Full pigment finishes are usually used in the sections of hide which have more imperfections. Such leather may be buffed to correct any blemishes. These use an opaque inorganic pigment with a binder such as acrylic resin and are often embossed with a "faux" grain pattern.
If you are interested in a professional Vermont house cleaning service please go to our contact page and let us know. Nancy will be happy to discuss with you the details of your cleaning project.
Deerskin, for example, looks and feels quite like bos primigenius leather, though afficianados would certainly know the difference. Essentially any animal skin can be used. As a general rule hides from younger, unscarred animals will generally be used in higher grades of leather, while older and more blemished examples will be used for lower grades.
The process of transforming the raw hide of the animal into a usable product is called tanning.
In ancient times, tanning was considered a noxious trade, which is not surprising when one considers the techniques used. Raw hides were soaked in urine or left to putrefy before dipping into a salt solution. After scraping off the hair, tanners would pound dung into the skin, or worse, mix dung and water in a vat and knead it with their bare feet. We shouldn't be surprised that tanneries were relegated to the outskirts of town!
Times have changed. The modern tanning process is highly automated and now uses neither urine nor dung!
If you are interested in a professional Vermont house cleaning service please go to our contact page and let us know. Nancy will be happy to discuss with you the details of your cleaning project.
The first step is curing. At this stage excess moisture is removed and the hides are suffused with salt either through brine curing or by salt packing. Subsequently the salt is removed by soaking the hides in clear water.
Next is the process of liming. Hides are soaked in a solution of quicklime (calcium oxide) or other disulfide reducing agent like cyanide or an amine. The goal is to reduce the fat content as well as to remove hair and keratin. Any hair left after the liming phase is removed physically, first through a mechanical process and then manually to ensure a clean hide. A further pre-tanning process called "bating" may also be done depending on the type of leather.
At this stage the hides are ready for the true tanning process. Tanning is required to strengthen the collagen in the hide to make it more durable and resistant to decay.
There are two essential types of tanning: Vegetable and mineral.
Vegetable tanning uses a substance which occurs naturally in many species of tree bark called tannin (hence the name "tanning"). This is a slow process, requiring the skins be stretched for weeks in tannin solutions. Vegetable tanning is used largely for leathers which need to be tough and durable, such as for soles, belts and watch straps.
Mineral tanning typically uses chromium sulfate for processing (though some other methods such as tara-aluminum tanning are occasionally used). The method is ideal for items which need to be soft and supple such as jackets, handbags and wallets. Because this requires a low-pH skin to facilitate penetration of the chromium, the hides are pre-treated in a solution of salt and acid. Once the chrome has suffused the skin adequately, the process of basification is started. This raises the pH to more neutral levels. Mineral tanning is much faster than vegetable tanning. Processing time is measured in hours rather than days.
Synthetic tannins (called "syntans" for short) have attained widespread use. Whitish when finished, these compounds are similar to vegetable tans only they are derived through chemical synthesis rather than by processing organic materials like tree bark. Initially these were seen as poor substitutes for true vegetable tannins, however improvements in the process have meant they have become fully accepted in the tanning industry, especially for "retanning" before the finishing phase.
Once the tanning process is done the leather is piled down, wrung and split. Splitting separates the flesh from the grain layers. The grain layer is that which faces the outside of the animal and is used for smooth grain finishes. The flesh layer is on the inside and is eventually processed to produce suede.
The processes at this point diverge depending on the type of tanning. In the case of vegetable tanned leather, the skins have to be suffused with moisture, colloquially known as "horsing up", then allowed to dry for one to two weeks in a cool enclosure.
Retanning is usually used in mineral tanned leathers to stabilize the tanning agent. This prevents leaching and, in the case of chromium tanning, removes the characteristic blue color. In fact the retanning agent is often some combination of vegetable tannins and/or syntans. Since the syntans have a bleaching effect, these are commonly used for white or pastel shades of leather.
After retanning, many leathers are dyed to achieve a desired color. This is as much of an art as a science because of the differences in pigmentation of the retanned leather. To achieve a desired end color, adjustments may be needed on the basis of the pigmentation of the ingoing leather sheets.
During fatliquoring leather is strengthened and moisturized by using various "sponging" compounds. Which sponging compounds are used vary greatly depending on the desired qualities of the finished product. Glycerine, soaps, animal oils, epsom salt, bicarbonates, mineral oil, egg yolk among other substances may be used. Recently steps have been taken to reuse the natural fats removed in the preparation phase for use later in fatliquoring, helping to reduce cost and waste in production.
After fatliquoring, the leather goes through a process of "setting out". This compresses and smooths the leather. Finally, the product is dried to bring moisture levels down to normal, equilibrium levels.
There are a variety of finishes available for leather.
Analine finishes use analine as a dye. This is intended to have a natural look. Such finishes require consistent sections of high quality leather because any grain faults will be clearly visible. Calf leather is often finished in this way as it tends to be free of blemishes and is well suited to the soft, "non-invasive" technique. Aside from showing any faults in the leather, analine finishes require special care from the user since it retains a fair degree of porosity, and is susceptible to staining and water damage.
Pull up aniline uses a top treatment of oil and sometimes wax. Though these do offer somewhat better resistance to moisture, the finish may be compromised through rubbing and scuffing.
Full pigment finishes are usually used in the sections of hide which have more imperfections. Such leather may be buffed to correct any blemishes. These use an opaque inorganic pigment with a binder such as acrylic resin and are often embossed with a "faux" grain pattern.
If you are interested in a professional Vermont house cleaning service please go to our contact page and let us know. Nancy will be happy to discuss with you the details of your cleaning project.