When the substance is reduced to fine powder, the painter begins to incorporate the oil with it. He has a _grindstone_ of marble or porphyry, on which he places a small quantity of the dry colour, and moistens it with a little oil. With a large flattened pebble, called a _muller_, he then grinds up the powder with the oil, until both form a perfectly smooth paste. That portion is then removed by a palette knife, (which is a broad thin knife,) and placed in an earthen paint-pot. Another small portion of powder and oil is ground up in a similar manner, and put into the paint-pot; and so on, until a sufficient quantity has been obtained. When this is done, the pot contains paint, which is too thick for use; to liquefy it, therefore, a given quantity, which is determined by experience, of oil or turpentine, or a mixture of both, is added, until the paint has acquired a consistence--thick enough to prevent it from running into drops when laid on the work--and thin enough to make it work with ease. The Process of Painting. Supposing the carpenter to have left the doors, the windows, &c., in a clean and smooth state, the painter’s first office is _knotting_. Knots are round places in a plank, in which the grain of the wood runs through the thickness of the board, so as to show the ends of the pores at the surface. These ends absorb a greater quantity of paint than the other portion of the wood, so that if the same number of coats were given to all alike, the knots would have an ugly, dead appearance, in consequence of the absorption. The painter, therefore, gives the knots more paint than the rest of the wood-work; and the preparatory coat, which is laid on the knots only, is called the _knotting_. The paint used is generally red lead, and boiled oil; or sometimes red lead and size. When this knotting is dry, the _priming_ is applied, consisting of a thin coat of white paint. White is used for the priming under almost every variety of circumstances, whatever the subsequent colours may be. This white paint is a mixture of white lead, linseed oil, and oil of turpentine, and is laid on, as are the subsequent coats, by means of brushes which are too well known to need a lengthened description. They vary from a quarter of an inch to three inches in diameter, and are generally made of hog’s bristles bound round with string, or sometimes with tin.