Carbon Swirls

Examples of carbon swirls, black ribbons or swirls through the insulator, the result of foreign matter in the glass, often organic material such as sawdust that oxidizes releasing tiny gas bubbles that trap the black residue in the glass. While uncommon, they generally appeal only to specialty collectors.

CD 106 with carbon swirls in skirt	CD 162 with carbon swirls
Carbon swirls around skirt of CD 154	Carbon swirls / bubbles in crown of CD 154