There are two main ways of tanning leather, the old-fashioned way VEGETABLE TANNING, and the new way CHEMICAL TANNING. The easiest way to spot veg tan is that it's usually thicker. Chemical tanning is quick and the chromium struggles to penetrate to the middle of thick hides leaving raw material in there. That is why you see so many laminated belts. It’s cheaper to use two pieces of chemically tanned leather glued together than one good piece of veg-tan.
Chemically tanned leather is essentially dead/static. With veg-tan, the vegetable matter (usually from barks and manures) enter the leather during a six-month long process and attach to the flesh proteins. That process continues after the leather is finished and you get a product that is constantly evolving.
The products of both kinds of tanning have their purpose. At Hassett Goods we prefer veg-tan because it suits our designs. If well looked after these traditionally tanned leathers can last for decades and gain a rich patina that improves with the years.