Marbling and graining is the painting of a surface, to give the appearance the it is made of wood or marble. The technique is at least 4000 years old, but was crude in style until around 1840 when British artist  Thomas Kershaw, took the art to level that has seldom been equalled. Sucessive  layers of transparent paint (glaze) are built up to give the work the illusion of depth and luminosity.   It is not uncommon to have a dozen or more layers of glaze on some marble. Arguments can be made about it being a cost effective alternative (not always true), providing a solution to problems of weight with natural materials, or even a creative ecological choice over endangered rainforest woods.  The best argument however, is that these techniques in the right hands can be simply breathtaking.