When straight lines occur in patterns that are blinded through the paper, it will be enough if the ends only are marked through with a small piece of straight line, and the lines completed with straight-edge and folder, after the paper has been removed.
Unless the finisher has had considerable experience, it is best to deepen all folder lines by going over them in blind with a fillet or piece of straight line.
When the pattern has been worked in blind, either through a paper pattern or directly on to the leather with the tools, and any inlays stuck on (see page 213), the cover should be well washed with clean water. Some finishers prefer to use common vinegar or diluted acetic acid for washing up books. If vinegar is used it must be of the best quality, and must not contain any sulphuric acid. Cheap, crude vinegar is certain to be injurious to the leather. Porous leather, such as calf or sheep skin, will need to be washed over with paste-water, and then sized.
Paste-water is paste and water well beaten up to form a milky liquid, and is applied to the leather as evenly as possible with a sponge. When the paste-water is dry, the leather should be washed with size. Size can be made by boiling down vellum cuttings, or by dissolving gelatine or isinglass in warm water.
For the less porous leathers, such as morocco, seal, or pig skin, no paste-water or size is necessary, unless the skin happens to be a specially open one, or the cover has been cut from the flank or belly. Then it is best to put a little paste in the vinegar or water used for washing up. When the leather is nearly, but not quite, dry the impressions of the tools must be painted with glaire. Finishers' glaire may be made from the white of eggs well beaten up, diluted with about half as much vinegar, and allowed to settle. Some finishers prefer to use old, evil-smelling glaire, but provided it is a day old, and has been well beaten up, fresh glaire will work quite well.
The impressions of any heavy or solid tools should be given a second coat of glaire when the first has ceased to be "tacky," and if the leather is at all porous, all impressions had better have a second coat.
As glaire is apt to show and disfigure the leather when dry, it is best to use it as sparingly as possible, and, excepting where the pattern is very close, to confine it to the impressions of the tools. It is not at all an uncommon thing to see the effect of an otherwise admirably tooled binding spoilt by a dark margin round the tools, caused by the careless use of glaire. Glaire should not be used unless it is quite liquid and clean. Directly it begins to get thick it should be strained or thrown away.