The word “cordovan” alludes to much more than just the pinnacle of quality in leather. Historically, it refers to a city that was the pinnacle of art, culture, and education in the known world, the culmination of centuries of war and many men’s lives: Qurtuba. Qurtuba, later called Cordoba (hence, cordovan) by the Spanish, was the capital of Islamic Iberia for around 100 years between 930 and 1030 a.d. Right around 929, a myriad of political and diplomatic conditions aligned in such a way as to grant the city of Cordoba an extended period of peace and the freedom to orient their culture towards leisure and finery; the library in Cordoba, for instance, was said to contain more books than all the other libraries in europe put together and its Great Mosque, referred to as a miracle of art and architecture, attracts visitors from all over the world still today. Prime amongst their artistic accomplishments was the Cordobans’ renowned mastery of leather arts, specifically tanning.

While it’s not exactly clear what the Cordobans did differently or how they made their leather such high quality, it is possible to speculate why they devoted so much time and effort to perfecting it. First, leather was used to bind the Qur’an. Cordoba was strongly Islamic and their ability to enshrine their holy book, which for them was the very presence of god on earth, in the finest materials available was a high priority. Although the most notable example of this is the elaborate tooling and gilding done to the surface of finished leather it would surely also have been important to develop finer tanning techniques to further enhance the book’s appearance. Secondly, it appears that a combination of fashion, availability of exotic animals, and ideal conditions for tanning (i.e. the quality of water in nearby rivers) turned the countryside surrounding Cordoba into a hotbed of leather production. The fact that the wealthy city of Cordoba was so nearby meant that the producers of these leather goods were encouraged by the Cordobans’ high standards and demand for luxurious goods to up the ante on quality and keep bringing leather into the city.

Regardless of exactly how, we do know that Cordoba became a center for the leather trade in the 10th and 11th centuries and that it had a monumental influence on the rest of the world in this regard. So much so that it permanently imbedded itself into the language used by other countries to describe leather and leather goods, specifically shoes. The french word for shoemaker, for instance, became “cordoanier,” which, transliterated into English, means cordovan-er; someone who works with cordovan leather.

“the leather work of Cordova became so famous that in the 11th century records of France the shoemakers were designated cordoaniers and leather as cordovan. It was to Spain that England and France owed their knowledge of the art of tanning and embossing as the English terms cordovan, cordwain (Spanish leather), and cordwainer (shoemaker) indicate.” (S.M. Imamuddin)

So it’s clear that the word Cordoba could hardly be spoken in the late 10th century without conjuring an association with high quality leather, but what about shell cordovan? Why is it that nowadays the word Cordovan is so inexorably tied with the shell layer of a horsehide? I’ll admit that I was only able to find very little information on this, so much of the following is admittedly conjecture, but it appears that tanning horsehide shell was something of a Cordoban specialty. The part of Iberia that Cordoba occupied was formerly home to the Visigoths, who seem to have been the first to tan horsehide shell. When the Moors invaded and took control from the Visigoths, their tradition of hide tanning remained and was adapted to cordovan tanning techniques to become shell cordovan. Because shell is so dense and famously difficult to tan, and because of Cordoba’s reputation for its leather, Cordoban tanned shell was likely the best, if not only, shell leather available in the medieval world. From there I can only imagine that horse shell became so closely associated with Cordoba that the connection remains today. Alternatively, there is also evidence to suggest that “Cordoban” became something of an adjective used to describe leather of the highest quality in medieval England and, because horse shell is arguably the finest type of leather available, the two became intertwined that way.

As for the material itself, shell cordovan isn’t exactly leather in the usual sense of the term. Unlike conventional leather, shell cordovan comes from a subcutaneous (literally: under the skin) layer of hide that is entirely unique to equines. The specific location and composition of this layer is something of a subject of debate (which sounds strange). While it’s clear that the shell is an oyster shaped region on the horses rump, people still argue about which layer of skin or hide the shell resides on. Different sources say different things, but few of them with much authority. Some say that it’s a surface layer of muscle and not even technically part of the hide while others say it’s sandwiched somewhere in between. As for its composition, I’ve seen people say that shell is made up of everything from a honeycomb-structured cartilage to a muscle called “panniculus carnosus” and none of these seem to be exactly true. The plain and simple answer is that these misconceptions stem from trying to understand horsehide in terms of bovine biology, whereas the truth is that horses have a third layer of skin and they are quite unique in this regard.

I finally started to find concrete information about this third layer in book published in 1923 by the Chemical Catalogue Company on “The Chemistry of Leather Manufacture,” which contains a few snippets about shell cordovan. I found this one particularly interesting:

“The dense mass of fibers, often called the glassy layer, can be seen running horizontally across the middle of the picture and appearing much darker than the remaining fibers. The portion of the hide containing the glassy layer is known as the shell and is used to make leather sold under the name of cordovan.”

This glassy layer, also called the “horse mirror,” is more properly called the “hyaline” or “hyaline layer,” which separates the epidermis from the corium. The hyaline is a layer of skin (present in all mammals) in which the fibers become “so tightly woven that there are no loose ends beneath the epidermis, thus, when the epidermis is removed, a smooth layer is revealed (called the hyaline layer), which gives the characteristic grain surface to leather” (source). As mentioned above, however, the hyaline in horses is unusually dense to the point that it takes on a glassy appearance. Furthermore, a horse’s hyaline is not only dense, but also incredibly thick. So much so that, rather than simply form a surface as it does in other mammals, it helps to make up an entirely different layer of skin so unique to horses that it is sometimes called the cordovan layer. This layer actually covers a large area of the horse’s body but is so especially dense around the rump (or crup) that it was designated the “shell.”

One final note on shell cordovan in the market today:

Its fantastic quality, combined with the difficulty of tanning, and the very small amount of it available per hide makes shell cordovan some of the most expensive leather available; Nick Horween, of Horween leather in Chicago, says it goes for about $100 / square foot on average. As one final note, it’s also worth mentioning that shell cordovan is especially scarce in the United States. Cow leather is relatively cheap because the hides are produced as a byproduct of the beef industry; i.e. the cows are raised primarily for meat and the hides provide extra profit. Americans love to eat meat so there are plenty of hides. On the other hand, we don’t exactly like to eat horses. Not only that, even if we did, most states have laws against raising horses for human consumption and congress passed a law that virtually prohibits USDA inspection of any such facility; which you need in order to operate legally.