The first process in marbling is the preparation of the size on which the colours are to be floated. This is a solution of _gum tragacanth_, or as it is commonly called, gum dragon. If the gum is placed over night in the quantity of water necessary it will generally be found dissolved by the morning. The quantity of gum necessary to give proper consistency to the size is simply to be learned by experience, and cannot be described; and the solution must always be filtered through muslin or a linen cloth before use.
The colours must be ground on the marble slab with a little water, as fine as possible; move the colour from time to time into the centre of the marble with a palette knife, and as the water evaporates add a little more. About one oz. of colour will suffice to grind at once, and it will take about two hours to do it properly.
Having everything at hand and ready, with the size in |71| the trough, and water near, the top of the size is to be carefully taken off with a piece of wood the exact width of the trough, and the colour being well mixed with water and a few drops of _ox gall_, a little is taken in the brush, and a _few very fine_ spots are thrown on.
If the colour does not spread out, but rather sinks down, a few more drops of gall must be carefully added and well mixed up. The top of the size must be taken off as before described, and the colour again thrown on.
If it does not then spread out, the ground or size is of too thick consistency, and some clean water must be added, and the whole well mixed.
If the colour again thrown on spreads out, but looks rather greyish or spotty, then the colour is too thick, and a little water must be added, but very carefully, lest it be made too thin. If the colour still assumes a greyish appearance when thrown on, then the fault lies in the grinding, and it must be dried and again ground.
When the colour, on being thrown on, spreads out in very large spots, the ground or size is too thin and a little thicker size should be added. Now, if the consistency or the amount of gum water be noticed, by always using the same quantity the marbler cannot fail to be right.
If the colours appear all right on the trough, and when taken off on a slip of paper adhere to it, the size and colours are in perfect working order.