As an excess of grease is apt to dull the gold and soil the leather, it is better to use it very sparingly when laying on fresh gold for mending. For patching, benzine may be used instead of grease. When the gold is picked up on the cotton-wool pad, rapidly go over the leather with wool soaked in benzine, and at once lay down the gold. Benzine will not hold the gold long enough for much tooling, but it will answer for about half-an-hour, and give plenty of time for patching.
Imperfect tooling arises from a variety of causes. If an impression is clear, but the gold not solid, it is probably because the tool was not hot enough, or was not put down firmly. If only one side of an impression fails to stick, it is usually because the tool was unevenly impressed. If an impression is blurred, and the gold has a frosted look, it is because the leather has been burned, either because the tool was too hot, or kept down too long, or the preparation was too fresh.
To mend double or burnt impressions the leather should be wetted and left to soak a short time, and the gold can be picked out with a wooden point. When nearly dry the impressions should be put in again with a cool tool, reglaired and retooled.
It is very difficult to mend neatly if the leather is badly burnt. Sometimes it may be advisable to paste a piece of new leather over a burnt impression before retooling.
If a tool is put down in the wrong place by mistake, it is difficult to get the impression out entirely. The best thing to do is to damp the leather thoroughly, leave it to soak for a little while, and pick up the impression with the point of a pin. It is best not to use an iron point for this, as iron is apt to blacken the leather.
Leather is difficult to tool if it has not a firm surface, or if it is too thin to give a little when the tool is struck.
When the tooling is finished, and the loose gold removed with the rubber, the leather should be washed with benzine, to remove any grease and any fragments of gold that may be adhering by the grease only.
The inside margins of the boards are next polished and varnished, and the end papers pasted down. Or if there is a leather joint, the panel left on the board may be filled in (see [Chapter XVII]).
When the end papers are dry, the sides and back may be polished and varnished.
It is important that the varnish should be of good quality, and not too thick, or it will in time turn brown and cause the gold to look dirty. Some of the light French spirit varnishes prepared for bookbinders answer well. Varnish must be used sparingly, and is best applied with a pad of cotton-wool. A little varnish is poured on to the pad, which is rubbed on a piece of paper until it is seen that the varnish comes out thinly and evenly. It is then rubbed on the book with a spiral motion. The quicker the surface is gone over, provided every part is covered, the better. Varnish will not work well if it is very cold, and in cold weather both the book and varnish bottle should be slightly warmed before use. Should an excess of varnish be put on in error, or should it be necessary to retool part of the book after it has been varnished, the varnish can be removed with spirits of wine. Varnish acts as a preservative to the leather, but has the disadvantage, if used in excess, of making it rather brittle on the surface. It must, therefore, be used very sparingly at the joints. It is to be hoped that a perfectly elastic varnish, that will not tarnish the gold, will soon be discovered.