Jim Flanagan of Fremont Antique Glass blowing antique glass.
When it comes to "antique" or "restoration" glasses in the United States, the one that has the largest footprint is cylinder blown glass. It can be referred to as antique blown glass, mouth blown glass, hand blown glass, but they are all describing the same historic process of glass manufacturing. This process of window glass manufacturing became prevalent in the 1800's and continues in limited production today.
In this type of glass the process is to draw or gather molten glass out of the glass furnace and form a molten blob of glass on the end of a blow pipe. Through a gradual process of adding air the bubble and reheating, turning and swinging the molten glass a cylindrical bubble is formed. During this phase different surface characteristics are introduced to the glass. These surface distortions can be in the form of various sized bubbles or "seeds" in the glass, striations or straw marks and other degrees of surface textures. Once the desired size and texture is achieved the glass is removed from the blow pipe and a glass cylinder or muff is then put into an oven for annealing, a process of gradual cooling.
Flattening cylinder glass.
After the cylinder has cooled it can then have the ends removed leaving a glass cylinder. This cylinder is then scored and a fracture is achieved in the glass along the length of the cylinder. The glass cylinder is now ready for flattening into sheet glass. Once again the glass will be placed into an oven and heated to approximately 1,250º F. At this temperature the glass will once again be in a pliable state and can be flattened into a sheet form. The newly formed sheet will then be removed from the oven and placed into an annealing kiln again for gradual cooling.
There are only two glass manufactures making mouth blown window glass in the U.S. today. Fremont Antique Glass in Washington state and Blenko Glass in West Virginia.