Two types of glass are popular for lampworking. Each type has its own properties and they cannot be mixed together.
Soft glass: Soft glass is also known as soda lime glass and it consists of 70% silica, 15% soda, and 9% calcium oxide. It is the most common type of glass produced, and is also the least expensive. It comes in a huge array of colors and special effects. Typical brand names used in lampworking are Moretti/Effetre, Bullseye, Vetrafond, Lauscha, and CIM.
Hard glass: Hard glass is also referred to as borosilicate glass or boro. This is the same as Pyrex which is used for laboratory vessels and cooking containers. Boro is considered more forgiving to work with when compared to soft glass. It has a lower COE which makes it less likely to crack during lampworking than soda-lime glass.
Boro has a narrower working temperature range than soda-lime glass, has fewer available colors (although the color spectrum is gradually improving), and is more expensive. Also, its working range is at higher temperatures than soda-lime glass, therefore requiring a larger torch and greater oxygen pressure. Boro glass consists of 70% silica, 10% boron oxide, 8% sodium oxide, 8% potassium oxide, and 1% calcium oxide (lime).
