Until the mid-20th century, those of mass-produced books were covered in cloth, but from that period onwards, most publishers adopted clothette, a kind of textured paper which vaguely resembles cloth but is easily differentiated on close inspection. Most cloth-bound books are now half-and-half covers with cloth covering only the spine. In that case, the cover has a paper overlap. The covers of modern hardback books are made of thick cardboard.
Some books that appeared in the mid-20th century signature-bound, appear in reprinted editions in glued-together editions. It is often difficult to find a copy of such books stitched together in their original format. They are sought for aesthetic and practical reasons. A variation of the hardcover which is more durable is the calf-binding, where the cover is either half or fully clad in leather, usually from a calf. This is also called full-bound or, simply, leather bound. Library binding refers to the hardcover binding of serials and paperback books intended for the rigors of library use. Though many publishers have started to provide "library binding" editions, many libraries elect to purchase paperbacks and have them rebound as hardcover books, resulting in longer life for the material.
Methods of HardCover Binding
Oversewing, where the signatures of the book start off as loose pages which are then clamped together. Small vertical holes are punched through the far left-hand edge of each signature, and then the signatures are sewn together with lock-stitches to form the text block. Oversewing is a very strong method of binding and can be done on books up to five inches thick. However, the margins of oversewn books are reduced and the pages will not lie flat when opened.
Sewing through the fold, where the signatures of the book are folded and stitched through the fold. The signatures are then sewn or glued together at the spine to form a text block. In contrast to the previous method, through-the-fold books have wide margins and can open completely flat. However, the text block of a sewn-through-the-fold book is not very secure, which can cause some signatures to come loose over time. Many varieties of sewing stitches exist, from basic links to complex decorative stitches. While Western books are generally sewn through holes punched along the fold, some Asian bindings, such as the Retchoso or Butterfly Stitch of Japan, use small slits instead of punched holes.
Double-fan adhesive binding starts off with two signatures of loose pages, which are run over a roller "fanning" the pages to apply a thin layer of glue to each page edge. Then the two signatures are perfectly aligned to form a text block, and glue edges of the text block are attached to a piece of cloth lining to form the spine. Double-fan adhesive bound books can open completely flat and have a wide margin. However, certain types of paper do not hold adhesive well, and, with wear and tear, the pages can come loose.