When thin leather is colored with a dye, the color usually penetrates all the way through. On leather that is thicker in nature, such a a belt, the edges will be colored as a separate step. The tanning method of the leather has a lot to do with how a dye will penetrate as well. Vegetable tanning is the most common method sold today. However the older method of tannning
(using salt, animal parts, and other natural ingredients) may be found in small batches from a custom leather tanning supplier. The EPA made it clear the toxic nature of that method was to be greatly regulated inside the USA.
