Monthly Archives: February 2010

Glass Furniture

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Can you collect glass furniture? Sure you can. But keep these things in mind: if you care going to use it as well, you need to be very serious about protecting it from breakage or scratching. You are also going to be willing to give up a wooden piece if you find a glass replacement unless you have a lot of space.

By furniture, I am not talking about shelves with a glass door, or a curio vitrine. I am talking about furniture predominantly made out of glass. In some cases, glass furniture is easy to acquire. Look at a clear or black glass dining table. It is at least half glass. For dining chairs though, you are going to have to settle for wood, chrome and/or leather. If a glass chair is available, it is probably an art piece and not intended to be functional.

There are also clear and black glass tables for end tables or a coffee table. If they are considered part of your glass furniture collection, the key is to make sure they do not get scratched. Cleaning should be often and thoughtful, or you will damage the surface.

In my books on cut glass I have seen a reference to a cut glass table. It was a pedestal table, and both the pedestal and the top are made of cut glass. It was made for by a cut glass manufacturer for one of the international exhibitions that occurred in the late 19th century and the first half of the 20th century. No doubt more than one has been made over the years, but tracking such down may take time. An antique dealer might be the place to start to find one. It would make a marvelous addition to a library or living room.

A glass bed existed at one time. It also was created to exhibition purposes buy a glass firm in New York State. I doubt it was at all functional, and has been lost to history. A glass bed – some statement, even if you can’t sleep in it.

Still thinking about collecting glass furniture? It can be done, and you will not have many calls to buy once you get past the glass table made today. But when the call comes, have lots of money available, because the older glass furniture is going to be pricey. And let me know how it goes.

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How Glass Is Made

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OK, for those of you who like to know how things are made, here is a brief lesson in making glass, the material itself.

First, the raw ingredients are placed in a pot. These include:

  • silica sand (usually washed to remove extraneous material)
  • soda (originally ash from plants, now potash which is mined) to make the silica melt at a lower temperature
  • lime (to make the soda glass insoluble) from lime stone, and later flint (from which we get the term flint glass)
  • any colorants needed.

Cullet, recycled glass, can be used in part to make up the silica portion of the mixture. The exact proportions of the ingredients depends on the ultimate purpose for the glass and the manufacturer’s experience.

The pot is moved into the furnace, where the ingredients melt together. The glass is heated until all air bubbles have been removed. This takes place at 2400 degrees Fahrenheit (1315 degrees Celsius). The molten glass, also called metal (presumably because the same process is used in preparing metal for pouring), appears white-hot.

The temperature of the glass is dropped to 2000 degrees Fahrenheit (1100 degrees Celsius) for working. The glass itself has an orange glow. At this point mechanized processes for forming or molding the glass can begin. The glass loses heat to the molds forming it and loses the orange glow, but it is still too hot to touch. Each piece is cooled as it travels conveyor belts.  If cooling is slow enough, the resulting piece is tempered. If not, it moves into a lehr, where the heat rewarms the glass and it is left to cool slowly. This relieves any stress within the glass body so it is more robust.

For hand working, the glass maker works at a temperature between 1600 and 1900 degrees Fahrenheit (870-1040 degrees Celsius). A gather is taken out of the pot using a blow-pipe.  The glass worker forms the preliminary shape either by hand or in a mold. Using his lung power, the glass blower then inflates the vessel to the size desired. One of the great characteristics of glass is that at this temperature the item retains its shape as it is inflated: the item gets longer and larger around, but any surface details stay on the surface, stretching but not going away. As the glass cools during forming, it is returned to the glory hole to be reheated.

When the piece is complete, it is put in the lehr for annealing. The glass pieces are heated to between 800-900 degrees Fahrenheit (430-480 degrees Celsius), and left to cool slowly. The annealing process allows the structure of the atoms to realign themselves, which reduces the internal strain created by working the glass over and over to make the form. Without annealing, the glass may shatter with a light blow or even, eventually, crumble. Glass which sluffs off parts of itself has “glass sickness.”

Once the glass body is complete and cool, it can be further treated with sand-blasting, acid-etching, faceting, polishing and/or fuming to produce the final product.

For the curious: for window glass, the molten glass is directed in a wide, thin ribbon from the pot onto molten tin, where the glass floats away. The glass cools as it gets further from the furnace, and is eventually taken from the tin bath onto rollers, and directed into machines to apply any chemicals needed and into the cutting machines which finally cut the glass into sheets. Glass made this way is called float glass, and its invention in England in the 1950′s revolutionized the window glass industry.

For more details, see the Wikipedia article on glass.

Go to the Table of Contents to see all topics covered so far.

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