Fig. 12From: After the paint has dried: a review of testing techniques for studying the mechanical properties of artists’ paintGeometry of a a Berkovich tip and b a spherical tip commonly used in indentation experiments on paint materials. The angle, \(\alpha\), is \(65.35^{\circ }\) for a standard Berkovich tip. The figure is based on images available in the public domain through Wikimedia CommonsBack to article page