Our crystal paperweights category includes shapes that are between 3/4" and 4" thick. The thinner shapes are great for 2-dimensional photo crystals. The 3-dimensional crystals require a minimum of 2" thickness. Rectangular blocks, diamonds, square cubes and the obelisks can be 2D or 3D because they are at least 2" thick. All photo crystals are engraved on the inside of the crystal shape and not on the surface.