When etching on granite, the laser melts the surface of the stone, altering the polish on the surface of the granite. Although the depth of the image is less than that of a human hair (approximately 20 microns) and is discernable to the touch only as a slight roughness, the image becomes a permanent feature of the stone and will not wear off except to the extent that the stone itself wears. Granite is the hardest stone that is commonly used in decorative applications, and is the only one recommended for use in flooring (signs, logos, designs), since granite will not wear appreciably unless foot traffic is extraordinarily heavy. Laser etched floor inlays have been in place for many years with no noticeable wear on the image.

Absolute Black granite is the most popular variety for laser etching, due to its relative clarity, with very small crystals visible in the stone. The larger the crystals and the more variation in the granite, the more distracting the background becomes, and the harder it is to see a graphic image etched in the granite. Very bold images can be effectively etched on other types of granite, sometimes using a technique called “inverting”, in which the image is left in the polished granite, and the background is etched away. This can be an excellent way to display a corporate logo, for example, or other relatively simple designs. For detailed work, however, such as photographs, small text or other complex images, Absolute Black is the most effective granite medium.

More information on granite can be found at:

http://en.wikipedia.org/wiki/Granite

http://uts.cc.utexas.edu/~rmr/

http://www.fi.edu/fellows/fellow1/oct98/expert/granite.htm

http://www.granite-sandstone.com/granite-information.html