Very fine particles of other materials such as titanium white may appear opaque, black. The large difference in the refractive indices of the particle and the mounting media creates a thick dark border. At low magnifications only this border and not the transparent center of the particle is observed. At the left, photographs of titanium white are taken with 5,20,50 and 100x objectives. In each case the particles appear opaque.

Note: color differences are due to lighting variation.