Float Glass

Float glass is more commonly known as window glass. Because it is inexpensive and sometimes free, it is a popular glass to use in glass fusing. There is a rainbow pallet of compatible frit and powders to use for decorating and embellishing float glass.

Please note: All float or window glass may not have the same COE. There are different manufacturers who make this glass, and they are not concerned with the COE. It is normally around a COE of 82. You will need to experiment with your glass to be sure it is compatible, or just use the same piece of glass for your work. If you get a sheet from one source and a second sheet from another source, there is no guarantee those glasses will be compatible.

There is not even a guarantee that window glass made from the same manufacturer will have the same compatibility. If you are making a large item, or want to use a lot of window glass, purchase it in large quantities so that it will come from the same production run.

Some people ask their local glass shops, or window installers for their discarded glass. This will definitely save you money.

Window glass is made by melting sand, limestone, soda ash, dolomite, iron oxide and salt cake. This molten glass is then fed through a delivery canal into the float bath or tin bath. This method of making the glass gives it a even depth and a flat surface. Because of this process, some tin is absorbed into the glass. This can cause an invisible haze on one side of the glass.

When using float glass, this haze may affect the applied colored glass. To eliminate this problem do a test firing on your glass. Fire two pieces of glass from the same sheet. Cut two pieces, and flip one side upside down. Now fire these pieces. Keep track of which side of the glass has a haze. The tinned side can also be determined by using an ultraviolet light.

A short wave UV flashlight, or a UV-C Light pocket purifier is a good way to determine the tin side of the glass. Prolonged exposure can harm your eyes, so don't use this product any longer than necessary. These flashlights or pocket purifiers can be found on line, and vary in price. Use the correct wavelength, which is short wave or germicidal. Turning down the room light will help when testing with this light. There will be a fuzzy white glow when the UV light is on the tin side of the glass, and a purplish shine on the air side of the glass.

Some helpful information about float glass…

  • Float anneals somewhere around 1080.
  • Float glass is stiffer and therefore slower to soften.
  • Some float glass has no tin side. Some glass that is thought to be float is actually horticultural glass. Horticultural glass is a rolled glass, therefore it has no tin side. This glass is also very prone to devit. Check with your supplier to be sure the glass you are purchasing is either float or horticultural.
  • The tin side of this glass is softer and easier to scratch. This side will also leave a visible ghost-layer within the piece.
  • Float glass is more prone to float bloom. This is a white discoloration on the tin side of the glass. These can appear as stretch marks with some gaps between the frosted areas. It can be mistaken as devit.
  • During the fusing process, the tin side is less likely to devitrify.
  • Float temps are about 80 -100 degrees Fahrenheit hotter than Bullseye as a general rule.
  • A wide variation in texture and level of devit can be accomplished dependent on degree and speed of the heating process, the size of your pieces, and the type of kiln used.
  • Take the low and slow strategy. Since float glass is soft enough to blow bubbles at 1450, stay well below that temperature. Firing slow also allow you to get away with lower top temperatures.
  • Firing tin side down into molds to avoid the tin bloom on top of the finished piece.
  • Firing tin side down will yield a shiny surface and a foggy bottom.
  • Fire air side to enamels. Don't fire enamels on the tin side.
  • Fire as few times as necessary.

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