Today, Jamestown's Glasshouse recreates the manufacturing process used by glassmakers at Jamestown over 400 years ago. Today's glassmakers use many of the same techniques and tools utilized by their predecessors in the 17th century. The modern demonstration area sits just yards away from the remains of the original furnaces used by glassmakers in 1608 and 1621.
Glass is made of the combined ingredients sand, soda ash, potash and lime. In 1608, the colonists used the natural resources found here: sand from nearby beaches, burned sea weed for soda ash, wood ash converted to potash, and oyster shells slowly burned in a kiln to make lime. [Today, these ingredients come already mixed for the glassblowers and they are melted in the furnace overnight at a temperature of about 2350°.] The heat inside the furnace causes the mixture to become a flexible material, molten glass, which can be shaped into useable glass products.
The large furnace in the center of the demonstration area is the main furnace. On one side of the furnace is an opening called the "working hole". Just inside the working hole is a large pot that contains about 500 pounds of molten glass. When this molten glass is brought out of the working hole it is a bright orange because it is hot---about 2000°. On the opposite side of the furnace are several round openings called "glory holes". These are reheating chambers with temperatures inside at about 2200°. As a glassmaker works with the molten glass, it cools quickly requiring the glassmaker to reheat it in the glory hole several times until the shaping process of the glass product is finished. Once the shaping process is complete, the glassmaker places the piece into the "lehr", which is a cooling structure set at about 890°. The lehr keeps the glass from cooling down too quickly and breaking.
The sources of energy that fire today's furnaces-natural gas and electricity-are not what the glassmakers used over 400 years ago. They used wood from trees such as hickory and oak, known as "hardwoods". By the 17th century, England lacked enough hardwood forests to support glassmaking, which is one reason why the colonists attempted this industry at Jamestown: the nearby abundant natural resources. Today's glassmakers can make glass daily whereas 17th century glassmakers could only make glass 4 or 5 days a month. Much of their time was spent cutting wood and gathering ingredients to make glass. They chopped enough wood to build a two story house and had to stoke the furnace fires day and night for almost two weeks to get a "melt" so they could make glass.
The color of glass is determined by different materials added to the mixture. Green is the natural color of glass because it is made mostly of sand, which contains iron oxide (rust), which causes glass to be green. To create clear glass manganese oxide has to be added to the mixture; blue glass is created by adding cobalt; white glass by adding tin; and brown glass by adding carbon. It is believed only green glass was made at Jamestown in the 17th century as the ingredients needed to produce other colors were not available here at the time and probably not sent over here from England.
Although glassmaking failed at Jamestown, it was the first industry attempted in English North America.
Last updated: May 13, 2015