This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Knotting is the material used by painters to cover over the surfaces of knots in wood before painting. The object is to prevent the exudation of turpentine, etc, from the knots, or, on the other hand, to prevent the knots from absorbing the paint, and thus leaving marks on the painted surface. Ordinary knotting is often applied in 2 coats. "First size" knotting is made by grinding red lead in water and mixing it with strong glue size. It is used hot, dries in about 10 minutes, and prevents exudation. "Second" knotting consists of red lead ground in oil, and thinned with boiled oil and turpentine. Patent knotting is chiefly shellac dissolved in naphtha. Following is a recipe for a similar knotting: - Add together 1/4 pint japanners' gold size, 1 teaspoonful red lead, 1 pint vegetable naphtha, 7 oz. orange shellac. This mixture is to be kept in a warm place whilst the shellac dissolves, and must be frequently shaken. Sometimes hot lime is used for killing knots. It is left on them for about 24 hours, then scraped off, and the surface coated with size knotting; or if this does not kill the knots, they are then painted with red and white lead ground in oil, and when dry rubbed smooth with pumice.
Sometimes after application of the lime the knots are passed over with a hot iron, and then rubbed smooth. When the knots are very bad they may be cut out, or covered with silver leaf.