Basic Glass

wrote this description for a student who wanted to understand the types of glass that are most popular for Flame-working. (melting the glass with a torch)
The difference between glasses are the fluxes, or compounds that are added to the silica. Some make the glass melt at a lower temperate (soda & lime), some make them heat resistant (boron), more reflective (lead), shatter proof etc…
Each type of glass melts at a slightly different temperature and more importantly have different ways they need to be cooled down to room temperature from the molten state. These differences are described as coefficient of expansion, or COE.
Borosilicate is melted at a relatively high temperature and soda lime at a lower. It is sometimes referred to as, Boro, Hard Glass, Labrotory Glass or Pyrex. Working with Boro is almost like driving standard, it takes longer to heat and is stiffer. It is also used for laboratory apparatus and you can buy it in tubes and rods.
Soda lime is the type of glass used in most furnaces, or hot studios where people use blowpipes and punties. This glass is referred to by many names too, Soft Glass, Italian Glass, Furnace Glass. Until hobbyist started making glass beads, you had to pull your own colour cane at a hot studio, but now there are many companies in the states that make pre-cut, ready to go rods.
I also describe soda glass is the breaky kind, you have to introduce it into the flame slowly, whereas boro you can pretty much stick right in the flame. Most people have quicker success with the soda and creating beads when they are starting out.
There are some great videos on y-tube. Just watching will help you understand the way the different glass moves.

Peace & love, natali

www.natali.ca