Research

Leather

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Interior Design
 
By: Christel Mononen, Pinky Ngai, Sarah Griffin, Vancouver, Canada

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Leather is the hide or skin of a mammal, reptile, bird or fish. Leather is one of the oldest materials known to man. Our ancestors used skins to clothe themselves and to keep warm. There are so many different types of hides and skins available from calves, goat, sheep, lamb, horse, pig, kangaroo, deer, reptile, seal, walrus and cowhide, which are most commonly used. Even nowadays there is still a great demand for leather, depending on consumers demand for beef. Leather continues to be a material of choice used around the world, not only for clothing, but also for interiors of cars and marine application.

Leather has a unique texture and color on each individual hide. Climate and the framing conditions affect the appearance of the hide. Cattle in the fields sometimes will be in contact with barbwire fences, trees and bushes that leave them with scars. The term hide is defined as the skin of large animals, i.e. cows, steers, horses, buffalo… In manufacturing upholstery cows or steers hide is generally used. Three or four hides are generally used for upholstering furniture, so that seams don’t show. There are only five percent of all hides that are picked each year, which are suitable for furniture and the rest used for garments.

If hides are not tanned or treated quickly, they will decompose and cannot be used for leather making. The two properties used for preparing the leather are called curing and tanning. Tanneries buy leather hides by pound from slaughterhouses. Hides with the hair still attached are called salted hides. Salted hides are shipped all over the world in packaged containers. Temperature of storing the hides is very important, so that the hides do not rot or become too dry.

All hides have a different texture left by the hair roots (called grain pattern); each animal shares its own unique structure. Older animals seem to have coarser pores, whereas young animals have finer ones. The top layer is called the grain layer, which contains hair patterns and the bottom layer is called corium layer, which is a looser fiber texture.

History of Leather
Like stone, wood and wool, leather is a natural product, a prized commodity throughout history. Leather upholstery was favored in the Renaissance, particularly by the Spanish and English. Techniques for embossing, tooling, painting and gliding leather were developed by Spanish craftsmen in the 16th and 17th centuries. Throughout this period, all types of furniture were covered with leather and studded with decorative nail head patterns. By the 18t century, the art of preserving hides and tanning them into leather was an old and respected trade. The tanning process took almost a year. Hides were coated with oil and grease, scraped, then softened by human foot power. Oxide and calfskins were preferred for late Louise XIV styles. Fine goat leather was often the choice of Chippendale and later designers.

The primitive people, who lived during the Ice Age some 500,000 years ago, were likely the first human beings to use the skins of animals to protect their bodies from the elements. As it is today, leather was a “by-product”: those ancient ancestors of ours hunted animals primarily for food, but once they had eaten all the meat from their kill they would clean the skin by scraping off the flesh and then slinging it around their shoulders as a crude form f coat. Furthermore, they invented footwear out of necessity to protect their bare feet from rocks and thorns. These first shoes would hardly qualify for designer awards, as they consisted of pieces of animal skin slashed into a rough bag fitting loosely over the man’s foot and tied at his ankle wit thin strips of skin or even with vines. The main problem that primitive man encountered was that after a relatively short time the skins decayed and rotted away. Man with his limited knowledge and experience had no idea how to preserve this hides. As centuries past, it was noticed that several things could be done to slow down the decaying process. First, if the skin were stretched out and allowed to dry in the sun, it made them stiff and hard, but they would definitely last longer. In order to make them soft and supple, various oily substances were rubbed into pores of the skin. This process was useable, but could hardly be termed leather.

In any case, a great deal of time passed before it was discovered that the bark of some trees contained “tannin” or tannic acid, which could convert raw skins into what we recognize as leather. The fact that this was an effective method of preservation was undoubtedly discovered by pure chance. It is hard to substantiate chronologically at exactly what time this method materialized, although you will recall that the famous “Iceman”, dating from at least 5000 BC that was discovered in the Italian Alps several years ago, was clothed in very durable leather.

Somewhat later, techniques used by the American Indian were likely very similar to those used in this early period. The Indians took the ashes from their campfires, put water on them and soaked the skins in this solution. In a few weeks, the hair and bits of flesh came off. Leaving the raw hide. By working the hide with his hands and rubbing it with sticks, the Indian made the hide soft and pliable. The tanning, which was done in a solution of hemlock and oak bark, took about three months and the leather was again worked by hand. This method was similar to that used by mankind in numerous geographical areas throughout the early periods of human civilization.

Types of Leather
There are three types of Full Grain Leather: Finished Leather, Naked Leather and Grain Suede Leather.

1- Finished Leather
This is the most popular kind of leather because of its smooth and sanity finish. It has a breathable protective finish to it that makes it to be the most suitable for high traffic areas or contract use. You can maintain it just by wiping it with a cool, damp cloth, and for tougher spots, use a ph-balanced soap on a damp cloth and rinse.
2- Naked Leather
This type of leather has no surface finish other than dyes, so furniture that has been selected with this type of leather is recommended to be used in lower traffic areas. There is no barrier to prevent staining or spotting, so this should be kept in mind, when selecting this type of leather. The only was to clean this type of leather is to wipe the whole surface with a cool, damp cloth. Spot rubbing will only darken that one area; you must keep in mind that the idea of cleaning this type is to even out abrasions or stains.
3- Grain Suede Leather
These are full grain leathers that have been buffed lightly to raise the nap of the surface, which produces very soft suede. These leathers have received a treatment for soil resistance that increases its durability. To prevent staining, you should blot any spill right away; you should never let it sit. Grain suede leather can be maintained reasonably as any spill will bead and roll off. For regular maintenance, it should be brushed occasionally with a soft brush, and you can remove any general spots with a suede-cleaning block.

Full Grain Leather requires very little maintenance, it is not very demanding. It should not be abused by using wax or leather polishes, mink oils, saddle soap or other kinds of cleaners that may damage the leather by not allowing it to breath. Using these will eventually dry them out, causing them to crack. Under regular conditions, all that is needed is a wipe down with a damp cool cloth to clean it.

When taken care of properly leather can last a very long time, it is resilient, and can outlast some fabrics by many years. Woven fabrics change as they get older, and its beauty lessens with age. Leather, if taken care properly, ages gracefully, and adapts to its environment, and is expected to change. Anything can change its surface, even the oils from our hands help imrove the patina.

Leather Classifications and Grades
There are four classifications of leather: Aniline, Nubuck, Semi-aniline and Pigmented.
1- Aniline
This dying process helps produce beautiful feeling leather in its most natural form. The natural beauty of this leather is enhanced by subtle colors in the grain and the hide marks.
2- Nubuck
These leathers have been processed to raise fibers on the grain side of the hide to give the effect of Suede.
3- Semi-aniline
A light color and finish is applied to the leather to bring out the natural characteristics of the leather, and increases its resistance to wear. Doing these balances out and dye color abnormalities, and allows for a greater color range.

Leather arrives at the manufacturers in two kinds: Finished (corrected) Leather and Natural (uncorrected) Leather. It is also organized into different grades of leather depending on their finishes.

Finished or corrected leather includes grade 6, 7 and 8 after the curing and tanning process. The leather is then buffed, embossed and pounded to bring out its natural texture and softness.
They are graded depending on the time spent on correcting the leather, this means that grade 7 is not better than grade 6 and so on. Grade 6 is just as durable as any other grade of leather, maybe better because of its protection, but it might not feel as soft as the grade 7 or 8 Leather.

For high traffic areas, it is suggested to use grade 6 or 7 leather; it will become softer the more often it I used, and it will feel better. Grade 8 can be used as well for this purpose; it has just been processed for a longer period of time making it softer, and the color might not be as strong from fewer scars, burns or scratches that were covered because of it coming from a cleaner section of the hide.

Grade 9 and 10 leathers fall under the natural or uncorrected leather finish, and can also be called “naked” finish.

Grade 9 Leather is the natural hide, which has been dipped into a dye for a certain amount of time, then hung to dry. After it is dry, it can be buffed with sandpaper to give it a very soft feel, or can be given a texture by machine or by hand to give a unique look. It receives a protective coat against stains, but not as high of quality of protection as grade 6, 7 and 8.

Grade 10 Leather is considered to be similar in preparation as grade 9, except the quality of leather is a bit higher. It has fewer scars, burns and scratches, making the appearance a bit more even. After being dyed, it is hung for hours to dry, then tumbled to break the fibers down making it feel softer.

In tanneries, they come across on average %5 of hides are considered to be unmarked enough to classify as grade 10. The term “naked” means that there is a very minimum of protection that was applied in the preparation. It requires more care, when a spill or an accident occurs, but if you don’t mind the care of it you will have furniture that as the softest and the best feeling leather in the world.

Cost of Leather
The overall cost of leather is determined by its Grade. A sofa made from an almost flawless, top-grain leather, will cost anywhere from approximately $700.00 (a good sale on corrected grain leather) to around $6000.00 depending on the designer name or where you buy it from.
Prices also vary depending on what kind of animal the leather was from. If it is from an animal that is common, such as a cow, it will be cheaper than leather that is from an animal that is harder to acquire.

Care and Maintenance
Tiny dirt particles that are rubbed onto the surface of your furniture can wear it down leaving it shiny, and can thin the leather causing small cracks. Regular cleaning can prevent this.
There are many ways to take care of your leather furniture. Some of the basic methods are to vacuum leather with a soft brush nozzle often to remove dust, and to blot any spills immediately with a dry cloth and let air-dry. There are also creams and cleaners that if used regularly can lengthen the life of your furniture and keep it feeling soft and supple.
You can buy leather care products from furniture manufacturers and stores; the salespeople will recommend products for your furniture and its specific requirements.

The 6 and 12 months guideline for cleaning is a good idea to follow, and it makes it easier to remember. It is recommended that you use a leather conditioner every 6 months, and a leather cleanser every 12 months followed by a conditioning treatment. It is also suggested that if you live near the ocean, you should clean it more often, however, it is possible to over-clean or over-condition your leather. Most leather is treated with a coating to help prevent stains, and if you clean it excessively, you might wear away that protective coating. Basic rule for cleaning: Less is More.
If you do accidentally spill something onto your leather, make sure you wipe the area as soon as possible, and when it is convenient, apply a small amount of leather conditioner to the area. This will help prevent any marks from occurring.

Leather Repair
Leather is very easy to take care of it; it is timeless. Although stains are easy to remove, but tears and holes in the leather need to be patched. There are 10 steps to repairing torn leather. First you need to evaluate the damage. Secondly, the leather needs to be shrunk with a hot and cold method, using a heat gun or a dense metal for cooling referred to as a chill bar. The leather needs to be opened to patch the “through holes” with a large piece of leather or vinyl. Several other materials can be used for patching like rubber, fabric and plastics, applied with chemical activators or heat. The heat allows the patch to stick to the leather is called a heat cure compound. Next, the patch needs to be stretched and worked in through the hole, so that it sticks to the back of the hide. The heated compound is repeatedly applied to the hole until the hole is level and sanded smooth.

All leather has a texture, so a grain texture is added with a grain-mold. The grain-mold is pressed up against the leather, after the final coat of vinyl is applied and then the mold is slowly peeled away. There is also spray or grain texture using liquid graining method sprayed on through a mouth-atomizer. The glue used to patch the hole is transparent, so therefore it needs to be color matched to the leather, by using water based color in a leather and vinyl finish. Color should always be tested on small area, so that color will match up the leather. Leather is sprayed with an airbrush technique or can be brushed on or wiped on with a cloth. If material is heated, while it’s being sprayed, it is quicker to repair and will also produce the desire texture. After leather has been colored, clear topcoat should be applied and will give the leather its smooth shine.

Processing of Leather
Raw hide is made up of %70 water, so to process the leather it needs to be kept refrigerated or water needs to be removed, so that the hide does not rot. Hides are never clean to begin with so the need to be cleaned of blood, dung and of hair. Before the tanning process takes place, the hide needs to be cured by salting or drying them after being removed from the animal. There are two methods used for salting: wet-salting or brine-curing.
Wet salting is when the hides are piled on top of each other for 30 days, so that the salt will pervade the skin. Brine curing is much faster, which is most commonly used by placing skins in large tanks that contain a disinfectant and absorb full saturation in about 16 hours. The skin is then soaked in pure water to get rid of all salt residue, blood and dirt; this process takes from 2 hours to 7 days.
The flesh I removed mechanically from the inner surface and hair is removed by soaking the skin in a solution of lime and water, containing sodium sulfide for 9 days. The hair is the removed by machine and any excess hair or remaining flesh is scraped off by hand with a knife. This procedure is called scudding. Tanning is the first and most important part in processing the hide into leather, so it can be made into product. Tanning makes the leather resistant to bacteria.

There are 6 procedures used to process leather:
1- Curing
Curing is used to saturate the skins in salt.
2- Soaking and Un-hairing
Skins are soaked in water to eliminate salt, blood and dirt. Un-hairing the skin is done to remove the hair with a machine.
3- Deliming and Bating
Deliming the skins are soaked in acid to reduce swelling and “Bating” is a material used to give a flexible and smoother texture.
4- Vegetable, Mineral / Chrome Tanning
The three tanning agents are used to prevent the skin from decaying or shrinking. These agents for tanning are for different types of skins depending on what the leather is intended to be used for. Vegetable tanning is extracted from bark, wood, fruit and leaves of trees. Mineral tanning is a salt compound of chromium, known as chrome tanning.
5- Lubrication and Dyeing
The leather is lubricated with soap, greases and wax, and runs through a machine to give leather Thickness and high gloss. The process of dyeing is when the leather is put in a spinning drum with several colors to attain color and durability. After the dyeing, the leather is then stretched for drying.
6- Finishing
Lastly the leather is finished with a top coat with a finishing compound by buffing it with a brush-covered cylinder.

Availability
Leather Furniture can instantly create luxury and warmth in your home. While initially more expensive than fabric upholstery, leather is recognized as a better investment over time. Leather is also a comfortable material that ‘breathes’ – making it cool in the summer and warm in winter. The leather industry is one of the oldest industries known to mankind. Our earliest ancestors used skin to protect their body, hands and feet.

Leather is made from the skin of any animal, reptile, bird or fish through a process known as tanning. This process preserves the skin, which would otherwise quickly putrefy or decay. Because of its durability and comfort, leather has been used for seating purposes throughout the history of transportation and furniture.

The early leathers were made from cowhide, calfskin, pigskin, deerskin and goatskin. The hides and skins coming from animals either hunted or farmed for food purposes.

- Leather is highly aesthetic.
- It is fashionable.
- It is a natural product.
- It has status appeal.
- It is a comfortable material to be in contact with.
- It is extremely durable.

In the late fifties, the elegant but informal line of Scandinavian furniture design revolutionized furniture industry. The need for softer cushion-style seating catalyzed the development of upholstery leather that was softer, more flexible, sophisticated and yet maintained a good level of durability.

Traditionally, vegetable tanning was the method used to preserve leather, which resulted in firm, fairly unyielding brown color leather (similar to saddle leathers). The development of mineral tonnages resulted in leather that was softer, finer and more durable and does not deteriorate with aging.
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