So What Is Leather?
Obviously, here at Lake Leather we are in the business of selling leather products in Australia, and we pride ourselves on the quality of our product selection. We are able to choose our selection because we have a good knowledge of leather and its unique properties. Our owner Georgie trained for two years with the world-famous Society of Master Saddlers in the UK. This institution of leather craft has been building its leather knowledge for many centuries and sets the benchmark for quality leather production and leather craft.
Leather tanning has been conducted since ancient times, with evidence it was being done some 5,500 years ago.
But what is leather? Where does it come from and how is it made? And how do we tell the difference between good and bad leather. In this series of discussions, we will look at some interesting aspects of leather and the fine craft of turning it into leather products. In this article we will discover what leather is, how we turn skins into leather and discuss some of the unique characteristics these different processes will give to the hides.
What is leather?
Simply, leather is the skin of an animal which has been treated to make it resistant to putrification through the process of tanning. Most leather products in Australia are made from the hides of cows, but virtually any skin can be tanned. Other commonly used leathers are lambskin and sheepskin from sheep, pigskin from pigs, and kidskin and goatskin from goats. You will also regularly see deerskin, buffalo hide, camel hide and many others.
The tanning process essentially uses chemicals to change the structure of the protein layers within the skin, stabilising them to prevent decay. These chemicals are called tannins and can be found in many natural substances such as grasses and tree barks. Interestingly (and a little disgustingly), brain matter contains tannins, and most animals have a big enough brain to tan their own hide. Various chromium salts can be used as tanning agents and have been widely used since the industrial revolution. The different types of tanning agents give the leather different qualities, and we will discuss these differences briefly below.
The place where animal skins are tanned is called a tannery, the people conducting the work are called tanners.
Traditionally, tanning was a pretty disgusting process involving lots of unsavoury things like dog poo, buckets of urine and vats of noxious and dangerous solutions. Historically, it was considered an ‘odoriferous trade’ and tanneries were generally relegated to the edges of town or the poorer areas. Nowadays, sustainability and ethical production methods are forefront of development within the industry. Great strides have been made in reducing the harmful impact of leather production and it is a hot topic in industry discussion.
Curing- when an animal is slaughtered its skin is removed before the carcass cools, allowing it to be removed easily with little damage. In its raw state animal skin is prone to deterioration and putrification. Raw skins will usually be salted, or cured, to stop this putrification process beginning. Kgs of salt are spread on the flesh side of the skin, or the skins are submerged in a brine solution. Curing removes much of the moisture content from the skins, raises the pH level and increases cell pressure within the proteins making it an inhospitable environment for bacteria to grow. Skins will be packed and delivered to the tannery cured.
The next phase in the process is what is known as the ‘beamhouse operations’- preparing the cured hide for tanning. At this point the wet hides are thick, heavy, hairy and have much of the gore still attached.
Soaking- on delivery to the tannery the cured hides will be soaked in clean water to remove much of the salt and rehydrate the skins.
Liming- after soaking the hides are limed. This involves soaking them in a milk-of-lime solution. That is chemical lime, a base chemical derived from limestone, not the sort you might find in a gin and tonic! The alkaline properties of the lime solution can remove the hair or fur (depending on additional ingredients), and will start removing some of the unwanted proteins, remove natural greases, clean the hide and plump the collagen fibres so they are ready to accept the tanning agent.
Fleshing- the skins are scraped to remove any soft tissue still remaining on the skin. Any remaining meat fibres and connective tissues are now removed, usually using a series of rotating scraping blades. Traditionally, this would have been done by hand and been very labour intensive.
Dehairing- if required, chemical agents such as sodium hydroxide are added to the skin to remove the hair. Initially the dehairing is usually done mechanically, then finished by hand in a process called scudding. The grain is rubbed with a blunt blade to remove the hair or fur from the skin.
Deliming- acids are added to the skins which reduce the pH of the skins. The swollen fibres shrink ready for bating and the lower pH means the enzymes can work effectively.
Bating- bating is the process of softening the hides ready for tanning, through the action of enzymes. This is one of the most ‘odiferous’ parts of the process in historic times. Traditionally, bating would involve smearing excrement (e.g. urine, dog poo, bird guano) all over the hides and leaving for these some time. The hides would be worked on by enzymes produced through a fermentation process caused by bacteria from the excrement, and the high pH; nowadays purified enzyme extractions are used.
Pickling- the final stage before tanning can begin. The skins are treated with salt and then acid to prepare the collagen fibres for the tanning solutions. This process stops any ill-effects on the fibre structure from the rapid drop in pH.
Now that the hides have been through the beamhouse operations to prepare them, the actual process of tanning can begin. Tanning comes down to chemical processes within the structure of the proteins in the skins and we will not be getting too scientific in our discussion here. The process of tanning is an artform; anyone can have a go, but to do it well takes lots of knowledge, skills and equipment. There are many trade secrets within the industry: different tanneries, many being family businesses passed down for many generations have their own set of highly valued and guarded processes and trade secrets. Here we will have a brief look at the final stages of the different forms of tanning.
Tanning- the hides are immersed in the chosen tanning solution and left for varying amounts of time, depending on the tanning agent, to absorb the solution. Chemical changes occur within the structure of the collagen in the skin, differing depending on the agent used.
Vegetable Tanning- the skins are stretched on frames and immersed in increasingly strong tannin solutions. Vegetable tannins occur widely in nature, especially the barks and leaves of trees and other plants. Not to get too technical, the tannins bind to the collagen protein fibres and cause them to be less susceptible to bacterial attack. Veg tanned leathers tend to be thicker and stiff compared to chrome and other mineral tanned leather. Ideal for saddlery, footwear, belts, luggage and case making, furniture, and small leather products, veg-tanned leathers are highly valued for their natural beauty and deep hues. Veg tanning takes around two months and the process is mainly conducted by hand. It requires patience, skill and care to produce these beautiful hides. Veg tanning is less harmful to the environment as it uses natural compounds to tan the skins.
Chrome Tanning- chrome tanning is a much quicker process than veg tanning, often tanning a skin in as little as one day, being driven by chemical process rather than natural penetration. It requires careful coordination of pH, temperature and the addition of particular solutions at the right point in the process to complete the chemical changes. In essence, the tanning agent removes the moisture from the hide and binds with the collagen proteins making them much less prone to bacterial decay. The process is quick, effective, much cheaper than veg tanning, and the colours are bright and stable over time. It produces a much more supple and stretchy leather than veg tanning. Chrome tanned leather is ideal for handbags, upholstery and garment making. The major cost here is the impact chrome tanning has on the environment. Wastewater from tanneries can have a massive detrimental effect on the surrounding environment if it is not treated. This is particularly a problem in third-world countries where environmental protections are less stringent. We will discuss the pros and cons of these different processes at a later time and investigate the ethical issues and problems of the leather industry in another article.
Other Tanning Methods- there are many other methods of tanning leather. Many alternative minerals exist which will tan leather, such as aluminium, aldehydes, titanium, and zirconium. These are less commonly used than chromium salts in industrial tanning.
Natural tanning occurs when hides are immersed in environments naturally high in tannins such as peat bogs. Indeed, this is where evidence of some of the oldest examples of tanned leather are to be found today. Human remains naturally mummified in bogs have been found wearing tanned leather footwear. This snapshot of our distant past preserved in amazing condition over the eons has given us this insight into the development of leather making. This evidence from thousands of years ago shows that humans have been in possession of the knowledge of tanning since before our written history began.
Today we are faced with new and unprecedented ethical issues relating to the production of leather and the leather products in Australia that are used. The industrial scale the process is now conducted on has serious environmental impacts not considered in the past. We will look at these issues at a later time. I hope this article has been an informative and interesting look at the production of leather. The transforming of skins from raw and deteriorating animal hides into the beautiful natural material we call leather.
Until next time x