Leather Manufacturing: Good Practices And Things To Avoid
Being one of the determining elements of the quality of a pair of shoes it is normal to look into the manufacture of leather. Obviously it is not the only one, of course. But without good leather, even with all the goodwill in the world, your shoes will not last very long. As much as recognizing a good assembly or a beautiful seam is relatively simple, as much recognizing a good leather is much more subtle and complex. There is no miracle test, no clear, and precise answer. I do not pretend to be an expert but as I have spent quite a bit of time in the workshops and tanneries where I have been able to discuss with professionals in the sector I will try to give you some leads. In this first part, we will focus on the manufacture of leather which conditions its quality. One night, over a drink, I had a discussion with a friend on shoes and leather goods (especially leather belts) He believed that quality leather should be smooth and shiny. All the other leathers are less good. When I saw how this idea was ingrained in his head I said to myself that he should not be the only one. With great reinforcements of marketing campaigns, certain brands had succeeded in making him believe anything. I know that this article will have very little weight against these behemoths. But it has the merit of being there and allowing those who wish to know more about this material with a thousand faces, mysterious and fascinating, that is leather.
Leather manufacturing: from breeding to tanningUpstream of the tannery (which will transform the skin into leather) there are several economic sectors that are players in what is called the “leather sector”. Their influence is great on the quality and availability of the raw material. Note: all that follows is not necessarily true for so-called exotic skin: alligator, python, stingray, etc.
BreedingIn the case of common leathers (calf, goat, lamb, cowhide, etc.), the skins, for the most part, come from farm animals. Of course, these animals are not raised for their skin (unlike some reptiles) but to meet the needs of consumers for meat, milk, or wool. This stage of leather production is essential because the breeding conditions have a direct impact on the quality of the final product! You don’t like buying meat/eggs from animals that have been bred, poorly maintained, fed with questionable flours, sometimes poorly treated, etc. Because, beyond the cases of conscience for some, we all agree that this has an influence on the quality of the product. Well for the animal’s skin it’s the same thing! Forgive me the expression but an animal that has only the skin on the bones (as we can see in some countries) will not be able to give a beautiful leather. While a well-fleshed animal, cared for and pampered will give, at the same time, very good meat and quality skin! Take the example of parasites: an animal that is not treated/vaccinated risks being injured, being bitten and there will then be scars on its skin which will affect the quality of the leather made from its skin. The sinews of war are money and profit. You who read me and who have a pet, you are well placed to know that the price of a consultation – or worse of treatment – at the veterinarian costs the eyes of the head! You can imagine the costs that this can represent on a herd. And therefore the potential savings: what good is it to treat animals that go to the slaughterhouse?
The SlaughterhouseHere, more than the quality of the leather – although considering the practices of certain slaughterhouses which make the animal live enormous stress which inevitably has repercussions – it is a question of the price. The higher the demand for meat, the more skins are available to make leather, so the lower the prices (and vice versa). You could almost consider leather to be a waste recycling industry for the meat industry. The trader in raw skins intervenes very quickly with slaughterhouses because the skins are wet products (3/4 of the weight of skin consists of water) and extremely putrescible. If left this way the skins degrade in a few hours. They must be quickly dehydrated in order to stop the development of bacteria and microbes that degrade the skin. There are several methods:
- salting (it is the most used because it is more simple and economical)
- cold storage
The TanneryIn general, the tanneries are specialized in a type of skin (lamb, calf, horse, etc.). It is this specialization that gives the name of tannery or tannery. It’s like in a restaurant: are you skeptical when, on the same menu, you are offered a Savoyard fondue and a cassoulet? Well for the tanneries it’s the same thing! In addition, the leather industry uses products that can be very toxic to the environment and to humans. By working with French tanneries, subject to very restrictive legislation on the subject, we ensure that the manufacture of the leather used to make our shoes respects the environment. It is not without incidence on the costs considering the investments which the tanneries must carry out to respect these standards. When you see the environmental ravages in India or Morocco, for example, you understand why, in addition to quality, it is advisable to buy shoes made with French leathers. You treat yourself and in addition, you preserve the planet.
Transformation of the skin into leatherAfter selection, the tanner, therefore, returns with his lots of salted hides. Then begins a long process (finally more or less long depending on the tanneries) process of transformation of the skin into leather. Leather manufacturing begins! He has at his disposal a wide range of techniques and processes which will allow him to obtain very different finished leathers. It is an art that relies on long-standing know-how associated with modern techniques. It is the tanners who will give its characteristics to the leather:
- River work: skin cleansing.
- Tanning: transforming a putrescible material (the skin) into a rot-proof material (leather).
- Wrought iron: give the desired properties to the leathers (solidity, flexibility, etc.) and a basic color.
- Finishing: giving the leather its final appearance (color, relief, shine, etc.) and its surface properties (protection, etc.).
River workThe tanner begins to work with salty but above all very dirty hides! We cut up an animal and then salted its skin. You imagine the head of what the tanner recovers. You have to be damn imaginative to visualize the magnificent leather that we are going to obtain, right? It is, therefore, necessary to start by cleaning them in order to remove all the unnecessary parts:
- the epidermis
- soluble proteins
- subcutaneous tissue.
TanningCleared of hair and other residues, our skin is ready to be transformed into the leather. We then begin tanning. This involves fixing chemical agents in the skin to transform it into the leather. We, therefore, transform a skin, very hydrated and putrescible into the leather which is poorly hydrated, rot-proof and resistant. It is not a discovery for anyone there are several kinds of tanning agents:
- Vegetable tannins
- Synthetic tannins
- fast (24h max)
- cheaper than the others
The wroughtWe have turned our skin into the leather – and you must have finished your steak long ago. But we do not yet have a product that can be used for making leather objects. It does not yet have the necessary characteristics for this. This is the purpose of this step. In reality, it is not a single manipulation but the succession of several which will allow reaching the desired result by the tanner. First, there is the spin. Our freshly tanned leather is loaded with water and it will pass through a machine with cylinders covered with felt which, with strong pressure, will make it possible to lower the water content of the leather. Then comes the yard. It is a strategic operation. The tanner will judge each skin according to several criteria (possible apparent defects and their locations, thickness, size, etc.) in order to constitute homogeneous batches. The consequence of this classification is that when you buy leather you have several choices (from 1 to 10 depending on the tanneries) which represent the quality of the batches of skins. Note: there is no absolute classification. Depending on its commercial positioning, a tanner may judge a defect as downgrading while another does not. I let you, given the customers they have, guess how the skins are judged in the tanneries of Puy and Degermann where our leathers come from. Some tanneries must then split the skins. On one side a leaf containing the flower, on the other the crust. Twice as much material to sell with the same quantity of skins. It’s necessarily interesting, isn’t it? Afterward, in terms of quality, this is not what everyone is looking for. The skin is then neutralized in a fuller before removing all the residual acidity and facilitating the penetration of chemicals (yes it is very chemical leather… but at the same time you expected what to pass from skin of an animal to a luxury product?) of the following operations. Before being dyed, the leather is, in certain tanneries, retanned (yes yes), this makes it possible to homogenize its characteristics within the same batch and to prepare it for dyeing. We, therefore, influence the lending of the skin, the finesse of the flower and the firmness. I do not repeat my blah on money, time, etc … you must have understood since … time … This is then the stage called food. To give suppleness to the leather, we will make it absorb fat (fish oil in general). For shoe leathers, we will find 4 to 8% of the weight of the flat leather. This step is carried out just after dyeing, often in the same drum. Note: by adding more fat (20 to 30% of the weight of the leather) we will be able to waterproof it. We are talking about oily leather perfectly suited for making mountain boots… The leather is then again wrung out and then stretched to reduce wrinkles and folds. It’s drying time. A very important step for the final quality of the leather. It is a skillful dosage that the tanner must carry out: not too fast not to deteriorate the leather but not too slow either otherwise the tannery would have problems of profitability! This is how he chooses the most suitable process among those at his disposal: hanging drying, vacuum, frame or on ice. After drying the leathers may be slightly stiff. We will, therefore, re-moisten them slightly and stretch them to give them all their flexibility. We went from a raw skin from an animal to a magnificent (more or less depending on the case) leather skin. But have you ever noticed that there are leathers with a velvety appearance, others very shiny or others with a grain, right? This is the subject of the last part! Note: earlier I told you about your washing machine that you overload to avoid having to do two… it could also happen to you to save on laundry given the price it costs, right? Well, some tanneries do the same thing. The products used are very expensive and they do not put enough (savings, profitability, blah blah… always the same refrain) so much so that the leather is only tinted on the surface and not in-depth. We can then see, on the edge, the middle layer which is always bluish gray. It is there that the vice is pushed very far: some go as far as painting the edge of the skin or better make a small fold sewn so that it is not seen!
FinishingSo we end up with leather that has all the properties that the tanner wants: flexibility, thickness, etc. However, leather is not usable in this state for the simple reason that it is not necessarily beautiful but it is above all very fragile. The tanner will, therefore, more or less improve the aesthetics of the skin. More or less depends on the starting quality of the skin. You understand why, well before the start of the tanner’s work, it is very important to know the origin of the skins and therefore the breeding conditions. Before protecting it, the tanner will more or less correct the skin. Depending on the appearance of the surface (no flaws or presence of flaws) it will sand (or not) the leather. The most beautiful skins are not corrected and we speak then of full grain leather. A full grain leather without finish will make beautiful patinas on your shoes . It is the rolls of leathers, the thickness of the skin is not changed and we will then have very high quality leather… This is the one we use on all of our shoes. Then the more there are defects the more we will sand the leather to obtain a presentable surface. We therefore reduce the thickness of the skin and make it more fragile. On skin with few defects the sanding will be light and we will obtain a leather called flower-corrected. If the skin is really of very poor quality we will then sand it deeply and get what is called split leather (which is technically no longer leather and it is even forbidden by law to call it leather). In this case, the finishing will aim to “garnish” the skin and imitate the flower in order to… take for consumers the consumers that we are! However, there is only one case where sanding is not used to camouflage poor quality skin: the velvety leathers that are velvet and nubuck. What is commonly called suede or suede leathers are actually skins that have been sanded to give them this appearance. In the case of nubuck, the sanding, flower side, is very light and will not hide any skin defects. So if you are in the presence of real nubuck it is because you have before you a very good quality leather. We obtain a leather with a peach skin appearance and very fine and short “hairs”. For velvet, sanding is done on the flesh side (this is what makes the difference between these two types of leather). To make velvet we generally use skins with a coarse flower but which we do not want to correct (as explained above) to keep a leather with good mechanical properties. As we work on the flesh side, the appearance of the velvet will depend on the type of skin used (goat, veal, pork, etc.). But it is generally less thin and flush than nubuck. For these two kinds of leather, there is no protective layer. You don’t notice anything in particular? We sand the skin to improve its surface appearance (corrected flower or even crust of leather) but we also sand it to obtain a velvet or nubuck which are made on beautiful skins just to obtain a velvety appearance. How to make the difference? With manufacturers who are inconspicuous, it is even more complicated because they go so far as to carry out a fine sanding of the crust in order to obtain a velvety appearance close to nubuck or velvet. Be careful! You can generally recognize a velvet crust because the appearance is less fine and flush than nubuck… In short, back to our skin. It is now ready to receive finishing. If we are in the presence of full-grain leather with very little defect then the tanner will apply a finish called pure aniline (this is an abuse of language because the chemical aniline is no longer used because of its toxicity ). It is, therefore, a “very very” thin transparent layer that will make it possible to enhance the natural appearance and the incomparable feel of a full-grain leather of very good quality. If we are in the presence of full-grain leather with defects – but that the tanner did not want to correct to keep the designation full grain – of a corrected grain or a crust, we will achieve a pigmented finish. We will apply a more or less thick and covering layer depending on the importance of the defects to hide. The touch is not at all the same as a full aniline full-grain leather. We can also achieve an intermediate finish which we will then call semi-aniline (or sometimes just aniline to sow doubt in people’s heads). It is also possible (often with very good quality skins) not to apply a finish at all. We then speak of natural leather. The touch is totally inimitable, very silky but the leather is very fragile and very sensitive to external aggressions (light, friction, stains, etc.) Our leather is therefore almost finished … Unless you want to give it a particular look or insist on a specific characteristic. In this case, we will have, in addition, a mechanical finishing. This is how we give a more marked grain to leather… and thus make grained leather Without going into too much detail here is what we can do:
- Satin finish/graining: the leather is passed through a heated press with smooth or engraved plates in order to reproduce a pattern (reproduction of the crocodile, stingray appearance, etc.) or to smooth it out.
- Dry coarsening: allows to accentuate the natural grain but also to soften the leather.
- Smoothing: provides a very smooth and shiny surface (for example box type leathers)
- Binding: the leather is folded flower against flower in order to create fine wrinkles on the surface This is how, after 4 to 5 weeks in general, we get leather.
Leather manufacturing: the 4 main families
- Full-grain leather with aniline finish: It is a leather made on the skin with very few defects of which we have kept all the thickness. We applied a transparent and thin finish to keep the leather looking natural. They are very beautiful leathers, appreciated by connoisseurs and with an inimitable appearance.
- Full-grain leather with pigmented finish: We have kept the entire thickness of the skin but to hide the flaws we have applied a more or less thick opaque finish. We have a well-protected leather, easier to maintain but with a less natural appearance.
- Corrected grain leather with pigmented finish: The grain of the leather has been sanded to improve its appearance and then a thicker opaque layer is applied than the previous leather. We still lose a little more the aspect and the natural touch.
- Pigmented crust finish: Pn, therefore, sanded very deep (or split the leather) and a very thick, opaque layer was applied to it to garnish the leather. We have an aspect close to the previous leather but it is actually not very resistant and will deteriorate quickly even if it is well maintained. It is a low-end product.