This is glow in the dark glass, Pyrex/borosilicate made by Mike Suchocki. The size of the circle is about 1.5 inches. The thickness is as thick as an average pencil. The glass is white in normal lighting. There are two colors available when glowing, yellow/green and blue. If you have a preference of either color let me know during checkout, if not I will surprise you. The black suede necklace is included, if you would prefer it can be sent with hemp string instead. The glass stays charged for hours. Blacklight or sunlight fully charges it in seconds. Any bright light charges it well.