There's optical science and high school physics, and then there's making pretty colors with this little 4-1/2" x about 1" acrylic prism. It makes the same rainbows that the beveled edges on the glass in the French doors to your grandmother's living room used to make on the floor in the afternoon while she was making supper. If you had a grandmother with French doors with beveled glass, who made you supper. If not, you'd better buy this prism or you won't have anything to remember after she's gone.

Polished glass equilateral prisms. Equilateral because each edge of the end is the same length. Thus, as all you geometry students know, each of the angles is also the same, 60 degrees. These are school grade and are fine for decorative and demonstration. They do a nice job of refracting light to produce a nice rainbow-like spectrum, but are definitely not up to instrumentation standards. Sides range from 23-25mm and the missing dimension, length, is shown below.