The coloring of marble has been practiced a long time, but heretofore its results have not been altogether satisfactory. It has always been considered a difficult process, and the piece of marble to be colored required great care in its selection, that it might be free from spots or veins. Heat, to open the pores of the stone so as to prepare the stone to receive the colors, has been considered essential. It is true that many of I the colors used would strike into the texture of marble while cold, but they would not sink to a desirable depth and the color remained upon the surface. The colors required and the vehicles employed to convey them to the stone have been numerous and various. Horses or dogs urine with lime and potash, lye from wood ashes, alcohol, oily liquors, spirits of turpentine, and wine, are men- i struums which have given some of the best results. The coloring matters used have been drawn from the animal, vegeta- I ble, and mineral kingdoms. Among them maybe enumerated, extracts of saffron, buckthorn berries, alkanet root, dragons blood, logwood, cochineal, gamboge, vermillion, yellow prus-siate of potash, etc., etc. The art of marble staining has been generally kept a secret by those who have achieved the greatest success in it. and has proved a lucrative employment. We have said that the results attained have not proved en 154 tirely satisfactory. Either the colors liave proved fugitive or changeable after a time, so as to impair the effect of the com binations in which they were placed, or the stone would net bear polishing after tlie process, or was only a surface color, liable to wear out when used for floors, steps, or in other situations whereit was liable to attrition. The superior advantages of a method which should impregnate the entire mass, as much in the interior as the exterior, and before polishing as well as after, are too obvious to be dwelt upon. Such a process is claimed by Dr. J. A. Weisse, of this city, ] who has for a long time been experimentin g in this field. We have not been put in possession of the details of this process, but we are able, from personal observation, to testify as to the results obtained. The stones are colored through and through, I not only marble but even granite having been subjected to the I process with entire success. We are informed that the process is based upon the discovery of a new mordant, which has such an attraction for stone that when a large block has only its base immersed in the solution, it will in a short time become permeated through the entire mass, increasing its specific gravity, and filling its pores so that the absorption of water is rendered very much less when subsequently exposed to the weather, than previous to the operation. When it is remembered that the absorption of water, and its subsequent expansion by frost is one of the greatest causes of disintegration in our climate, it will at once bo seen that an important collateral gain is obtained by the new process. Marbles colored by this process in the rough, afterward take a most beautiful polish, and specimens of dolomite polished previous to coloring have their polish hightened by it. An effort has been made in this process to imitate the means by which the valuable colored building stones naturally receive their color. No attempt is made to produce a given pattern, or to imitate any particular effect. The general tone of the color is produced and the variations of the tints are determined by the structure of the stone itself. In this way the effects are all natural. We have before us a piece of marble picked up in a common marble yard, of a cheap variety, one side polished the other rough, which has been colored by this process, and which the best judges invariably pronounce to be genuine Sienna marble. The colors produced include the entire range of tints, and the veins and spots which develop themselves in marble, which previous to the operation is pure white, are surprising and beautiful. The cheapest grade3 of stone are thus rendered ornamental and desirable, and the combinations rendered possible by this discovery must arrest the attention of architects. We do not exaggerate when we say that Some of the most excellent specimens of natural stones, celebrated for their beauty, seem dull in their colors when placed by the side of those prepared by this process. Their adaptation to church architecture, as well as the adornment of private dwellings, will be admitted by all who inspect them.