Paste is best made with old flour, water, and a little size or glue; alum is also added, to make it spread more freely without losing any of its tenacity or sticking quality. It should be brought to a slow boil and made rather thicker than ordinary gruel, and then allowed to get cool before using. It should be laid on the paper smoothly and equally, with a good brush, not putting on too much, or it will squeeze out at the edges. Where this takes place it must be renewed with a clean damp sponge. Any accidental smears of paste may be removed in this way, if taken off lightly as soon as they are made.