What Is glass?

Glass is an artificial material that has been used for around 3500 years to make a huge variety of goods for both function and beauty, with domestic and industrial uses. It has the virtue of being a flexible and versatile substance, and is easily manipulated when hot. It comes in many different colours and can be transparent through to opaque. When molten it can be blown, pressed, drawn into fibres, twisted, and otherwise shaped using many other techniques. When cold the surface can be engraved, cut, gilded, enameled, etc.

A myth that has been circulating around the beginners' glass community over the years is the "24 hour test", meaning if the piece does not crack within 24 hours it will never crack. This is completely untrue, it could crack at any time, even years later, the glass will hold it's internal stresses until they are relieved by either cracking or being annealed.

Another myth is that glass still flows at room temperature. A study was done a few years ago by researches looking at old church windows, what they found was glass thicker at the bottom of the pane than the top; they concluded from this that the glass was still flowing, and over the hundreds of years pooled at the base of the pane. The other explanation for this is that because window glass was made by blowing a sphere then opening up and flattening out (Crown Glass), you get left with a thicker part in the centre. When cut up, the stained glass artist naturally places the thicker edge so that it is pointing down, which is what the researchers found.

To make glass you need three basic ingredients; silica (sand), lime (for stability), and soda used as a flux to help fuse it all together. Other ingredients are used to provide clarity and colour to the batch.
All the ingredients are placed into a crucible and heated to between 1300 and 1500 deg C for up to 48 hours. During this period impurities that have risen to the top are skimmed off. For the purposes of lampworking, rods of glass are drawn down and cut into short lengths, ready for the lampworker to form into whatever shape is desired.

By leaving out the Lime, "Water Glass" can be made, this has a lower fusing temperature of around 800 deg C. Water Glass is so named because it is soluble in water.