Today we take for granted that if we purchase a book it will come with a protective paper or cloth binding but this has not always been the case. The concept of the publisher printing and binding a book is a relatively recent phenomenon, dating from the first half of the 18th century. Before the Industrial Revolution books were made entirely by hand, from the paper production to the typesetting to the binding.
Generally each part of the production was performed by a separate business but, in contrast to today, the binding took place after it had been purchased by the consumer. The bookseller sold the books in a crude protective paper cover with the expectation that the consumer would have the volume bound to their taste and budget. This explains why you can take six examples of a 17th century work and find they are all bound in different materials and different styles. Cheaper bindings would have paper covers or use cheap leather such as sheep. The brown leather binding we’re familiar seeing on rare books is calf while the most expensive bindings would use goat skin, commonly known as morocco. Morocco has an attractive grain and takes color well. More expensive bindings could also be extravagantly decorated with gold tooling.