Pewter is an excellent rust-resistant material with substantial weight. Pewter is soft enough to be easily bent by hand. To add strength to such soft material against easy bending, a hammer is used to beat the pewter to tighten the molecule structure, producing minute undulations as a result. It also changes the way the surface looks and improves the way it feels to touch. This was how the technique to create three-dimensional shapes from pewter was developed. The head of a hammer is used to beat small dents into the metal sheet, creating tiny undulations resembling the surface of a rock which is rough to the touch.