The basic tools for both carving and etching marble are the hammer and chisel. The sharpened end of the chisel is placed against the marble and the hammer is swung against the chisel's unsharpened end. The transfer of force causes the chisel to displace the stone and make a mark on the marble. Different sizes of both chisel and hammer are used depending on the amount of detail work that needs to be done.
Another tool for etching marble (as well as other materials, such as steel) is acid. The first step in this process is to get some contact paper and make sure that your etching design is printed on it. (Printing on contact paper means that the design is cut out of the paper, leaving small gashes removed from the contact paper.) This paper is then placed flat against the marble and a strong acid such as hydrochloric acid is poured over it. The contact paper doesn't react with the acid, so the acid will slide through the printed holes in the contact paper. In this way it will form the necessary design in the marble. The longer the acid is left in place, the deeper the etching's grooves will be.
Perhaps the most advanced method available for etching marble is to use a powerful laser to cut grooves into the stone. A photograph or other computer-rendered design is loaded into a computer that controls the laser. The computer will make all the necessary adjustments, determining the thicknesses and depths of lines, whether or not color will be present in the final etching and so on. Then the program is run and the laser follows the instructions from the computer, discoloring the marble to change the color or vaporizing it to create a groove.