Tanning Leather: The Tanning Process Explained

The process of tanning leather has been around for a good long while. Some trace it back to 1000 AD, while others argue that some of the earliest instances of the tanning of animal hide date back to before 6,000 BC! The exact date doesn’t really matter, though. Whenever it started, tanning leather is an old craft that humans have been perfecting for centuries.

Despite the longevity of this method, very few people know what tanning actually is (and no, it is not like tanning at the beach). It is a mysterious craft, and yet leather, its most common byproduct, surrounds us, from belts, bags, and watches to wallets, car seats, and baseball gloves. 

So, how is leather made, anyway? Here, we have a simple explanation of the entire process from rawhide to finished product. 

What Tanning Does and Why

These essential questions will make it clear why humans developed the tanning process in the first place. The answers will help you better understand the reasoning behind the processes used. 

Chemical Changes

On its most basic level, tanning changes the chemical composition of the hide. 

In particular, tanning targets the proteins within the cowhide and stabilizes them. This is a complex process that makes use of many chemical mixtures in order to target all the necessary proteins. 

What’s the Point of Tanning?

Since cowhide (or any animal hide, really) is made of organic material, namely skin, there is a possibility of that skin beginning to break down. If this process was allowed to continue, the hide would eventually fall apart completely. 

Instead, tanning aims to lock the hide’s proteins into a state where they cannot decay. From there, the product will keep the same durability that it naturally has, without the ticking clock of time acting upon it. Instead, long-lasting and durable material is born. 

Pre-Tanning Preparation

Before the actual action of tanning, a few actions are necessary, mostly to prevent the hide from breaking down. With the following steps, tanners are attempting to preserve the freshness of the hide.

Salting

Salting is one of the most helpful processes for keeping the hide in its original form. Our ancestors used salt to preserve all kinds of food and other organic materials. 

Salt is either pressed into the hide immediately after being removed from the animal or thrown into a brine solution and transported while in there. Either way, salting is the most immediate part of the prep.

Once the hide arrives at the tannery, it is soaked in water to remove the salt so that it doesn’t eat away at the hide. This is generally referred to as soaking, as the hides are thrown into a vat to sit. Once this step is done, the hides are dried and prepared for the next step. 

Liming

One of the more surprising chemicals used for tanning leather is the use of lime. Lime juice and milk form an alkaline solution that eats away at grease, fat, and hair left on the cowhides. This changes the appearance of the hides—they begin to swell and split in a way that helps them take in chemicals more efficiently. 

In this stage, tanners also remove the last of the hair and flesh, usually with machines but sometimes by hand. 

Deliming is the addition of a balancing chemical that draws out the compounds put into the hide through the liming process to ensure that we’re working with a supple material.

Bating

Bating is the act of adding enzymes that soften the leather. After the number of chemicals that have been added, the leather can sometimes harden, and the tanning chemicals will not penetrate as deeply or effectively. This step ensures that the hides are still easy to work with. 

Pickling

Pickling is not quite what it sounds like. This kind of pickling adds acidic chemicals that will make microscopic inroads within the hide for the tanning chemicals to penetrate to make the process more effective. 

Degreasing

This simple step is sometimes unnecessary. Adding water or other solvents to the hide will take the last little bit of grease off the hide to prepare for the long process of tanning and shaping. 

It is not always required, but the highest-level tanners utilize it. 

The Tanning Process

Now comes the star of the show: the tanning process. 

There are two major types of tanning that we see today. The first is vegetable tanning; the other is called chrome tanning. We will walk through the differences between these two and the advantages of both. 

Chrome Tanning

Chrome tanning is a modern method of tanning. It’s generally is used in large-scale tanning operations exclusively due to high costs. 

Modern machines are used to allow more acidic tanning agents to penetrate the hides more efficiently. The hides are first dipped into acidic salts for a bit to loosen them up, then dumped into chromium tanning agents.

This can be done in about a day and is the most common type of tanning that we see in the modern era. 

After the chromium has been absorbed, the hides are taken and shaken out to let dry. There may be a blue tint on the hides after that soon dissipates, but the hides are still referred to in this stage as “wet blue hides.” Machines then take the hides, cut them to the desired thickness, and shape them all in a short period of time.

Vegetable Tanning

Vegetable tanning has been around for a long, long time. It has its roots in northern Italy but was likely used even before then. 

Tanners mix together leaves, bark, vegetables, and other organic material into different drums of various strengths. Over the course of several months, the hides are moved from drum to drum for different stages of tanning. 

This slower process better preserves the original grains from the animal hides and is generally thought of as a gentler process. This is also where the distinct leather smell comes from. The rich, woody feel and smell are a direct product of the leaves and bark that impart their properties to the hide. 

The Difference Between the Chrome and Vegetable Tanning

In the most basic sense, chrome tanning is used in large, industrial settings, usually with lower-grade leathers, because of its speed and effectiveness. If the leather is to be dyed after tanning or turned into genuine leather, chrome is most effective as it does the job quickly and quite well. 

On the other hand, vegetable tanning is most common in higher-grade leathers. It is thought of as more of a craft and less of a manufacturing process. 

Great leather can be made with either process, though. As with anything, there is a good balance in the industry between the two. However, Andar’s full-grain leather will come from vegetable tanning for our quality line of products. 

Tanning Is a Process Indeed

As you can tell from our short run-through of the process, tanning leather has many steps, from acquiring the hide to the finished product in your hand. It has to go through phases of preservation with salts, liming, bating, and pickling, then to the actual tanning process. All of this is done before even being shaped into a bag, wallet, or other leather product! 

It is a joy to be in a field with such a history that requires an intimate knowledge of so many parts of the process. Next time you pick up an Andar product, don’t forget the time it took to make it, and know that we loved doing so! 

Sources:

Products of animal skin from Antiquity to the Medieval Period | JSTOR 

A Brief History of Salt | Time