Included Foreign Matter
Examples of included foreign matter (inclusions), usually pieces of fire brick from the glass furnace, but there can also be small rocks from the sand mixture, nails, screws, bottle caps, or other items. These will often cause cracks in the glass as the insulator cools. Some collectors specialize in pieces with inclusions, especially identifiable objects like nails.
CD 154, embedded rocks or pieces of fire brick with resulting milk swirls.
CD 154, detail of large rocks or pieces of fire brick embedded in crown.
CD 154, showing cracks in glass caused by embedded foreign matter.
CD 162, partially melted foreign material that prevented the lettering from fully forming.
Inclusion of foreign material in a CD 162
CD 162 with piece of firebrick.
CD 154 with a stone (left); detail (right).