I purchased 7 clear glass prisims from an antique shop.

I, too, have such crystals, of various shapes. I have a small window in my foyer, facing West. I used small brass nails in a row above the windows to hold the crystals that I tied with clear fishing line, each crystal ties from its wire loop to a brass nail. I situated them at different levels on the window. Because the sun sets in the West, we see beautiful rainbows on our walls from the sunlight shining through the window, especially in the afternoon. This of course could work well in the morning by choosing an East facing window.

I love hanging crystals in the windows. I have them in just about every window and depending on the time of day I get rainbows in different rooms. In the mornings I have rainbows in the kitchen, in the evening I have them going across the living room walls and floor.