Bubbles

Examples of bubbles, either included in the glass, or accumulated at the top of the mold resulting in voids in the drip points; the result of air trapped in the glass batch, foreign material dissolving in the glass and releasing gas, or incomplete mixing of the glass ingredients. These occur as single large bubbles, a collection of smaller bubbles, or thousands of tiny bubbles (seed bubbles). All are relatively common, although some collectors value them.

A large bubble in the skirt of a CD 162.

Bubbles in the crown of a CD 154, the result of
organic material dissolving in the glass, which also produced black carbon swirls.