THE SIZE.
The first process in marbling is the preparation of the size on which the colors are to be floated.
By the name of size is meant a consistent glutinous mass, which is obtained by boiling or dissolving with water certain bodies derived from the vegetable kingdom.
Mucilage is found in many plants, especially in the outer skin of seeds, also in many roots, barks, stems and leaves, but its solubility and consistency are very much varied.
Generally the mucilage of plants is classed among the gums; but there is a large difference from them in this, that it will not give a perfect, diaphanous and homogeneous solution, but only swells in it to a thick, massy and viscous fluid, which is similar to starch paste. It is composed of small quantities of gum, starch, sugar and consistent plant-mucilage. If prepared from certain plants, for example the algae of the sea, it also contains small quantities of iodine.
Starch swells in hot water, while with mucilage the same result is achieved by using cold water.
Smaller quantities of mucilage are found in every plant, but larger in gum tragacanth, carrageen or Iceland moss, salep, the leaves of mallows, or of colts foot or tussilage, the roots of marsh mallow, seeds of plantago-psyllium, (flea-bane) linseed and quinces.
Of this number but few are of interest to us, which I shall mention further on.