This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
92. The pigments described in the preceding pages are received from the manufacturer in the form of powder, and must be mixed or ground with oil to prepare them for use. This work is usually done in a color mill, where the pigments are ground in large quantities by manufacturers, from whom they may be purchased in the form of a thick paste; but where the painter prefers to mix his own colors, he may do so by grinding them on a color slab with a muller, such as is shown in Fig. 2. This consists of a semiellipsoidal stone, about four inches broad across the flat base, and sufficiently high to permit it to be grasped by both hands. Mullers smaller than this are likely to become rounded on the flat surface from unequal pressure, and in this condition are practically useless. The color slab is a flat piece of porphyry or other close-grained stone, upon which the pigment is placed preparatory to grinding.
93. Grinding is accomplished by mixing the powdered pigment with a sufficient quantity of linseed oil to form a thick paste, and grinding it under the muller by moving the latter backwards and forwards under pressure, lifting the advancing edge sufficiently, at each stroke, to cover the pigment which has been squeezed out from under. The pasty color must be frequently scraped up from the edges of the slab and deposited in the center to come under the strokes of the muller; this is usually done with a thin blade called the palette knife, shown in Fig. 3. This consists of a very flexible steel blade, with dull edges and a rounded end, set into a hard wood handle. There are several sizes, varying from four to twelve inches in length, but the larger ones are usually termed stone knives, as they are never used for any other purpose than mixing the pigment and oil for the slab, while the palette knife is also used for mixing colors on the palette as described hereafter. After sufficient color has been ground on the slab, it is scraped up with the stone knife and placed in a tin pail, or paint pot, and thinned down with oil to proper consistency for use. The operation of grinding with the muller may have to be repeated several times, in order to prepare a sufficient quantity of paint, but not till it is all ready is it thinned down for use; a quantity of drier may then be added, to cause the paint to harden more quickly, or varnish put in the mixed color, to cause it to dry with a glossy surface. In preparing paint for use, boiled oil is generally used to thin it down when it is intended for outside application, unless it is for decorative work, in which case a little turpentine and some pale linseed oil may be added. For indoor work, linseed oil, turpentine, and a little drier are generally used in varying quantities, according to the finish desired. The smaller the proportion of oil used, the less will be the gloss, and the greater the ultimate hardness of the coating.
94. Another blade used by the house painter is the stopping knife, shown in Fig. 4. This is a stiff blade with parallel edges and pointed end, used to stop or fill cracks, nail holes, etc., with putty before the painting is proceeded with. Stopping is not resorted to until after the first coat of paint is laid, as the pores of the wood are likely to absorb the oil from the putty, and render it brittle and inadhesive.
95. The palette, Fig. 5, is used by the painter to prepare his colors when executing small work, such as sign painting, interior decorations, etc. It consists of a thin piece of wood, either rectangular or elliptical in form, with a hole near one end, through which the thumb is inserted to hold it when in use. On the palette the various colors are mixed with the palette knife until the desired shade is attained, and the brushes are then dipped in the mixed color as it lies on the palette, instead of in the paint pots, as is the case with the colors mixed in large quantities for a general house painting.
96. If the colors on the palette are too thick to be applied with the brush, they may be thinned down with linseed oil, to hold which, a palette cup is used. This is a little tin vessel about two inches high and one inch in diameter at the top, as shown in Fig. 6. It is secured to the palette by means of a tin spring clamp on the bottom, which grasps both sides of the wood and holds the cup and oil in a handy position for the painter to dip his brush and thin down his paint.