dealt with vegetable-tanned leather. I
have used, with some success, chrome-tanned calfskin. Chrome leather
is difficult to pare, and to work, as it does not become soft when
wet, like vegetable-tanned leather. It will stand any reasonable
degree of heat, and so might perhaps be useful for top-shelf bindings
and for shelf edging. It is extremely strong mechanically, but without
further tests I cannot positively recommend it except for trial.

While the strength and probable durability of leather can only be
judged by a trained leather chemist, there remains for the binders
selection, the kind of leather to use, and its colour.

Most of the leather prepared for bookbinding is too highly finished.
The finishing processes add a good deal to the cost of the leather,
and are apt to be injurious to it, and as much of the high finish is
lost in covering, it would be better for the bookbinder to get rougher
leather and finish it himself when it is on the book.

The leathers in common use for bookbinding are:--

Goatskin, known as morocco.
Calf, known as calf and russia.
Sheepskin, known as roan, basil, skiver, &c.
Pigskin, known as pigskin.
Sealskin, known as seal.

_Morocco_ is probably the best leather for extra binding if properly
prepared, but experiment has shown that the expensive Levant moroccos
are nearly always ruined in their manufacture. A great many samples of
the most expensive Levant morocco were tested, with the result that
they were all found to contain free sulphuric acid.

_Calf._--Modern vegetable-tanned calf has become a highly
unsatisfactory material, and until some radical changes are made in
the methods of manufacturing it, it should not be used for
bookbinding.

_Sheepskin._--A properly tanned sheepskin makes a very durable, though
rather soft and woolly, leather. Much of the bookbinding leather now
made from sheepskin is quite worthless. Bookbinders should refuse to
have anything to do with any leather that has been artificially
grained, as the process is apt to be highly injurious to the skin.

_Pigskin._--Pigskin is a thoroughly good leather naturally, and very
strong, especially the alumed skins; but many of the dyed pigskins are
found to be improperly tanned and dyed, and worthless for bookbinding.

_Sealskin_ is highly recommended by one eminent librarian, but I have
not yet had any experience of its use for bookbinding.

The leather that I have found most useful is