Leather is best described as an organic material created by the tanning of animal rawhide and skin. The tanning process is necessary to preserve rawhide without which it would otherwise decompose. Furthermore, the tanning process allows different finishing techniques making a durable and flexible material from the rawhide. Leather can be made from almost any kind of rawhide, but the most often used is cattle hide.
There are several tanning processes that transform hides and skins into leather, but the most common are vegetable and chrome tanning (and a combination of those two). Vegetable-tanned leather is tanned using natural tannins from tree bark, wood, leaves, fruits and roots. Vegetable tanning was the first technique used since humans started using animal skins for clothing and protection. The leather produced by vegetable tanning is supple and brownish in color, depending on the mix of chemicals and the color of the skin. Vegetable-tanned leather is the only one suitable for use in leather carving or stamping. Vegetable-tanned leather is not stable in water; it tends to discolor, and in contact with water (after drying) will shrink and become less supple, and harder. Historically, it was occasionally used as armor after hardening (cuir bouilli process), and has been used for book binding as well. Today vegetable tanned leather is often used for fine leather goods and exclusive items from Louis Vuitton and Hermès, to mention a few.
The chrome-tanning process is a far more recent invention. Chrome-tanned leather is tanned using chromium sulfate and other salts of chromium. It is more supple and pliable than vegetable-tanned leather and does not discolor or lose its shape as drastically in water as vegetable-tanned. The process is much faster, thus cheaper, than vegetable tanning. Due to the fact that more esoteric and vibrant colors are possible using chrome tanning, the majority of the leather goods are produced by this process. Visually, chrome-tanned leather differs from vegetable tanned by a blue line in leather cross-section.
I will often use vegetable tanned leather and not leather dyed by the factory. This gives me the flexibility to dye and finish the leather according to specific design requirements. For large parties I use factory dyed leather because of the consistency of color and finish. I use mostly cow and calf hides and sometimes lizard, fish and snake skins for the top layer of the strap. I can easily obtain ray, ostrich, shark and crocodile skins as well, depending on requirements.