Each of these prisms is made of optically worked glass and is in the form of narrow isosceles triangles.
These prisms are designed to provide a progression of ideas from the principles of refraction in prisms to the properties of lenses.
When these prisms are placed base to base, a convex lens may be simulated and a concave lens maybe simulated, when placed vertex to vertex.
Students can appreciate and understand the working of a prism. Also it will become clear as to how in the case of very narrow prisms, the angle of the prism and the refractive index of the material affects the angle of deviation.
Various options in these prisms are available and they can also be customized as per one's requirement.