There are many different types of Restoration Glass available in the market place. The earliest form is a process called “Spun” glass or “Crown” glass. The glass is scooped out of a vat of molten glass on a long pipe and a ball is begun to be blown. The pipe is then spun and the centrifugal force spreads the glass out into a large “plate” form. In the old days, the flatter glass around the perimeter of this “plate” was cut into lites for window glazing. This window glass is rarely made today. The center of the “plate” which was thick and ringed with several concentric ribs of glass, is most popularly called “Bull’s Eyes”, “Roundels”, or “Crown Bullion”. They were used typically in locations to admit light into a building where it was not necessary to see objects through. Typically this would be in places like door transoms, where this glass is often used today. Green Mountain Insulated Glass, Inc. has access to this product and even has successful experience in turning these lites into insulated glass units.
Over time, glass making techniques improved. “Cylinder” glass or “Mouth Blown” glass was this improvement. This type of glass is made by dipping a large “pipe” into a vat of melted glass and at first blowing it into a ball. The softened glass is then swung over a pit while the artisan continues to blow, elongating the glass ball into a cylinder. This cylinder is then cooled, the ends are cut off, the glass is split down the length of the cylinder and put back into the kiln, and then flattened, removed from the kiln and cooled at the proper rate to anneal the glass. While this glass is labor intensive, it is an historically accurate method of producing glass common about 150 years ago. Usual features of this glass are: reams, bubbles, inconsistent thickness, and occasional manufacturer handling marks. The sheets are typically 6 to 9 square foot sheets.
The next significant improvement are that of “Drawn” glass and “Rolled” glass. Drawn glass is glass that is actually pulled out of a hot vat of molten glass with a special tool and Rolled glass is made from molten glass that is poured from a hot vat onto a table and then passed through rollers. Both processes achieve much more consistency in both optical qualities and thickness. The glass is characterized by slight to pronounced waviness, very occasional bubbles. And a very few manufacturer’s tool marks. These sheets are larger and because of their thickness and consistency, can sometimes be tempered. As with most glass, they also can be laminated.
The next great improvement in making glass, that is primarily used today, is that of “Float” glass. Lord Pilkington is credited with inventing the process in the late 1950s where the hot glass is “floated” out onto a molten bed of tin. This glass is able to provide us with the optical clarity which we see in our windows today. However, when it is desired to only have a very subtle hint of distortion; modern float glass can be put back into the kiln and reheated to remove some of the glass’s flatness and optical clarity. This “Faux Restoration” product will sometimes be the given look a customer is desiring. Because of the degree of control available during this process, the distortions available can be slight to significant and be similar to distortions characteristic of earlier glasses mentioned above. Sometimes dust is even introduced into the kiln to create a pitted appearance. While Faux Restoration glass is not made with a truly historic process, its appearance might be exactly that which a given customer desires.
There are other very old and new; decorative or obscuring patterns and processes available to Green Mountain Insulated Glass, Inc. for use in our products. An example might be that of “Glue Chip” glass which is made with an antique process in which hot glue is spread onto glass as it comes out of the rollers. The glue cools at a different rate from the glass and chips off an organic pattern from the surface of the glass, similar to the fern leafy pattern sometimes seen on a frosty window. Green Mountain Insulated Glass, Inc. almost always either has in stock or is able to acquire and work with any given kind of glass our customers specify. We are happy to work with our customers on their custom products.