The darkeners generally used are logwood, lime, brown, soft-soap, dyed oil, and various chemicals, such as aquafortis, sulphate of iron and nitrate of silver. An intelligent manipulation, however, of the stains themselves will render special darkeners unnecessary, for in most cases the required depth of color can be obtained by repeating the stain, or by darkening it for a second wash, and a small quantity of coloring matter may also be mixed up with the varnish.

When it is desired to deepen the natural color of woods, or to restore such as may have become discolored by time or other circumstances, the process called Improving is adopted, and this differs in no essential particular from staining, excepting that its object is merely to improve the color and bring out the natural grain of the wood itself, instead of attempting to make it represent another from which its veining may entirely differ. Barberry root boiled in water, Gamboge or Turmeric dissolved in spirit, give good yellow stains adapted for the purpose. A good red oil for rubbing discolored mahogany or rosewood, or for deeping the color of bay-wood, may be made in the following manner: Tie up some Alkanet-root in a muslin bag, and let it soak over night in some sweet oil. The oil which is then pressed from the bag will impart a beautiful red color to all the rest. The grain of the wood is well brought out by its being rubbed with ammonia before the oil is applied. Rectified naphtha, colored with Camwood dust, is another good red tint.

Discolored ebony may be improved by washing over it a strong decoction of gall-nuts in which a quantity of steel filings has been immersed, this liquid should be allowed to stand a day, and should then be carefully strained, and, as before stated, a little indigo should be added to the French polish. Raw oil mixed with a small quantity of turpentine serves to improve most woods when well rubbed into them, and this may be greatly enhanced in value by grinding up with it a small quantity of the color which it is desired to impart to the wood, or by mixing with it oil previously colored in the manner already described.

The well-known pigment called Gamboge is a gummy and slightly resinous exudation from the young wood of the Gamboge-tree. Though not a dye-stuff, Gamboge is much used in coloring, forming a valuable water-color, and is also used in coloring lacquer for varnish for brass-work. There is some reason to believe that Gamboge is made from more than one species. There are three kinds of Gamboge:

Pipe Gamboge, which is the best, it cmes from Siam in rolls one inch and a half in diameter and about twelve inches long, through which there is a hole about half an inch in diameter. Lump Gamboge, in masses weighing about one or two pounds, and having the appearance of a hardened yellow paste. Gamboge in tears or small drops.

Turmeric is the rhizone, or root-stalk, of a plant called the Curcuma longa. There are several varieties, of which the China and Bengal are considered the best. The colors produced by Turmeric are various and very beautiful shades of yellow. It is not as a dye-stuff considered permanent, but in the stains, when oiled or varnished, this failing is materially remedied.

Alkanet-root. The plant from which this root is obtained is of a diffuse character, rarely attaining a height of a foot. It is much cultivated in the south of France, and some portions of Germany. Its chief use is in giving a fine crimson color to perfumery and woods, for which purposes it is soaked in oil in the manner above described.

Cam-wood. This tree is a native of Sierra Leone, and has shining leaves and white flowers. It is of considerable size, often attaining the height of fifty feet. The stem is the part used, it is cut into logs about four feet in length, and these, after the removal of the bark and outer wood, are split and trimmed square for exportation, they are of a deep red color, and yield a brilliant red dye, which is rendered much deeper by sulphate of iron.