In time, the color of the exposed interior becomes more like the color of the surface because of the rock varnish's regrowth. There are several techniques for making petroglyphs. Striking one rock with another is called direct percussion . Indirect percussion refers to pecking the surface of one rock by holding a second rock as if it were a chisel and striking that with a third rock. A third technique, resulting in various line depths, is to scrape at the surface of the rock.
Pictographs are designs made by painting on rocks or in caves.
Colorful plants and minerals were ground up and mixed with protein based liquids such as egg, blood, or urine to make different colors of paint. The pigments were applied using sticks, brushes, fingers or hands. Rock Art was made by people all over the world. Much of it was made by prehistoric people. American Indians made most of the rock art in North America.