The sizing on these may vary as a result of the production process, optimally they are about 20mm. The dichroic adds such sparkle and depth to the bead which is very difficult for photography. Our new line of Coral Shimmers, the colors vary depending on the light here we get copper and coral colors. Each bead is completely unique as the application method and dichroic achieve a different result in each bead. The size is approximately 18mm LENTIL with a base of black Moretti Glass. They are exquisite. A dichroic filter or thin-film filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors (from Wikipedia) Dichroic Beads are a great way to upscale your Murano Glass Jewelry.