The glutinous matter used with mineral colors must be entirely free of any acids as the smallest particle of acid, which in warm weather is often formed after long standing causes an isolation of the coloring matter in such a way, that it will become curdled when thrown upon the size. The best glutinous matter, that can be used, is dissolved isinglass or parchment-glue with gum tragacanth. As the first two named materials are expensive they can be replaced by fine gum arabic free of acid. Take 4/6 of an ounce of gum tragacanth let it swell in 1 pint of water and dissolve fully by boiling. In this way we obtain a glutinous mass, which is mixed by stirring with a thick solution of gum-arabic. This mixture is used to unite the particles of the body of mineral colors. To grind the colors use a very smooth marble slab, a roller and a palette knife, of wood or horn, as those of steel produce some change upon red colors. The colors which are sold in the market are either in the form of grooved pieces, little cones, or powder. If the color is in pieces or little cones, it is first ground to powder in a dry state and is then mixed with a little water and from 10 to 15 drops of ox-gall to a thick paste. If a mineral color, add a piece of the glutinous matter the size of a nut, if, on the contrary, we have a lake color, the addition of water and gall is fully sufficient. Now commences the grinding. With a muller you continually run in a circular motion over the color using a moderate pressure of the hands. After about two or three hours have elapsed the color will have the requisite fineness which is shown by its greasy, lacquer-lustrous appearance. During the grinding, move the color from time to time into the center of the marble with the palette knife and at the same time the adhering color is removed from the roller. When the color is ground fine it must be diluted with water in a glass vessel and is then ready for use. Bottle tightly and keep it in a cool place, best in the cellar. For grinding the colors and diluting the same, river or rain water should be used, of course, proportionately to the quantity of color so that the latter will not become too thin. The grinding of a color is done mostly by apprentices as the time of a journeyman would be too valuable. In most cases this part of the preparation gives the greatest trouble, since the colors are seldom gotten to that fineness necessary to marbling. This is easily explained as the grinding demands practice and a certain perseverance. From the point of view that time is money, the majority of book-binders concluded to use ready ground colors and this was profitable to them as they could buy them better and finer ground and much cheaper. But, even here, we sometimes find articles, which leave much to be desired, but which, in most cases, can be used.