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How to Determine Colonial Glass

There are several methods of determining if an old glass bottle, plate or window is from the colonial era, which extended from 1492 to 1763. During this era, glass was blown without the use of molds, and contained different components which lent various features like weight and color. Glassmakers of this era were considered on par with nobility, due to the remarkable skill and stamina required to create objects from glass.

Instructions

- 1
  Look for any identifying marks on the glass, from seals, stamps, dates, names or even the pontil mark. The pontil is the area where the glass was broken away from the rough shape, leaving a smoothed, leveled and sanded hollow scar that can help identify the individual glass blower. There are no standards among these markings, but any mark may lead you to discover the glass' origins.
- 2
  Look for seams. Seams indicate the use of molds, and prior to the early 19th century, molds were not used. Any seam present means that the glass in question was not blown during the colonial era.
- 3
  Have the glass analyzed to find out what it is made of. Colonial glassblowers used lead and arsenic to improve the weight, color and workability of glass. These ingredients were used in conjunction with sand, potash, saltpeter and manganese. Some Colonial blown glass pieces may have been comprised of up to 1/3 lead, which was known as flint glass.

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