Managing corners is a skill required in many walks of life: car drivers ~ seamstresses ~ bookbinders. Here we outline some techniques used by bookbinders, and provide links to more details on the more popular methods.
This method is quickest and easiest. It leaves an exposed edge, and so the covering is not complete. If flush covering is acceptible then it is sensible on the grounds of economy of effort to flush-finish the coverings at the corners. One phrase I have heard used is that "...a bookbinder would never use flush coverings whereas a bookcrafter might well do it."
This ~ the most common method ~ involves a mitre across the corner. The mitre has to be cut in such a way as to completely hide the interior material. Therein lies the technique which is more fully described here .
Using this method results in the thickness of the cover at the corners having four layers of bookcloth over a very small area. This makes for unacceptable bulk when using thick covering material such as leather....read on...
Both the above methods may be used with leather. If binding with leather indicates quality of work then mitres are called for. If thick leather is used than this will require the leather to be pared down. Beginners ~ wisely ~ think twice at this stage. For them quarter binding is recommended. If the paring knife slips then a great deal of expense time and effort will be saved.
Vellum is harder and tougher than leather. Corners can be protected against future wear by the use of vellum quarter binding. It is often the practice to reduce the size of the vellum to very small pieces, foresaking the normal proportions of the larger quarter-binding pieces.
Round corners do not reduce the amount of wear on the corners, but it disguises the impact of daily battering. The time and skill in making a good round corner ~ or four ~ needs to be justified by the final price of the item. All the techniques of leather-paring need to be supplemented by patience and nimble fingers ~ and numerous tidy tucks with careful gluing.