BASIC FACTS ABOUT GLASS  

By Rebecca Markman, ISA CAPP, AM  © 2007

The beauty of glass has captivated humans for centuries.  There is evidence that glass existed in  early Mesopotamian civilizations, and examples of glass bottles, bowls and beads survive from Egyptian antiquity.  The main ingredient of glass is silica (sand).  It is mixed with other mineral substances to purify and/or color it.    In very basic terms, the recipe is heated to liquefaction in a  furnace, then man or machine works the molten mixture to shape it.  After the basic shape is created, surface decoration can be applied before the piece is annealed (cooled in a controlled way).  After cooling,  decoration can be engraved, etched or cut into the glass.   Lead was discovered to improve the sparkle, clarity and luster of glass in England in the 17th century.  Crystal (fine cut leaded glass) reached technical and popular heights during the American Brilliant Period of glass production (1880-1914).

Colored decoration can be applied in the mixture or painted later on the surface with molten glass, enamel (powdered glass) or gilding (metallic leaf or powder).  In the late 19th century, glass was sometimes cased (enclosed in another layer of colored glass) and cut, or refired and polished to produce certain color effects that were enormously popular.  In the 20th century, chemical painting or staining was invented to cheaply produce versions of these expensive wares for the masses. 

A short list of famous high quality American Art glass and Brilliant Period glass makers whose products very well could be in your home today: Dorflinger, Egginton, Fry, Handel, Hawkes, Hobbs Bruckunier, Libbey, Mount Washington, Pairpoint, Quezal, Steuben and Tiffany.  Items dating to the late 19th and early 20th centuries and in excellent condition are typically the most valuable.

A short list of famous high quality European Art glass makers that you might possess:  Daum, Gallé, Lalique, Muller Frères, Loetz, Moser, Murano, Val St. Lambert, Webb, WMF.  Again, the earlier production period Art glass in good condition is typically the most desirable.  Later 20th  and 21st Century production falls into a different market level as it is not yet rare or antique.

Basic facts about the care of glass: if you subject glass to sudden temperature changes or extreme heat or cold, it can crack.  Stacking glass without a protective layer or allowing it to contact other glass directly can cause chips and scratches.  If you leave liquid in glass, staining or clouding may occur.  Glass should be cleaned gently with warm soapy water.   Check the terms of your insurance policy; sometimes breakables are specifically excluded from coverage.

Rebecca Markman, ISA CAPP, AM  is a certified personal property appraiser specializing in 18th, 19th and 20th century American, British, and European antique furniture, tableware, silver, glass, porcelain, pottery and paintings.