Just about every one is familiar with the sight of the glassblower working with a furnace. It is easy to see why glassblowing is known as a “hot glass” technique!

There is another kind of glass forming activity which takes place at temperatures between about 600 and 930 Celsius ( 1100 and 1700 Fahrenheit) .This process uses a kiln to melt and shape the glass. Not quite as hot as the glassblower's furnace, this is known as “warm glass”

Only fragments of ancient vessels survive, but most scholars agree that the first kiln fusing and casting was done in Mesopotamia in the second millennium BC. The ancient Egyptians continued in the development of warm glass and by the latter half of the millennium became proficient in both casting and fusing.

The art reached it's zenith under the Greeks and Romans from the third century BC until the birth of Christ.

Glassblowing became more and more popular after this time. It was cheaper and more efficient and by the second or third century AD, warm glass techniques were almost forgotten…… The art lay dormant for many centuries!

However, in the 19th century the craft was re-discovered in Europe as a vehicle for artistic expression leading to the re-birth of kiln forming and the second flowering of the warm glass discipline. In France , Henri Cros, Albert Dammouse and Gabriel Argy-Rousseau developed Pate de Verre (paste of glass) techniques.

Many re-discoveries were made in the early years of the twentieth century in the USA , producing several artists such as Edris Eckhart, Maurice Heaton and Michael and Francis Higgins

Today, after two centuries of re-discovery and enhancement, warm glass continues to develop and grow as an artistic discipline.

Extracted from Contemporary Warm Glass, by Brad Walker.

The Process

Each piece of work is first designed and then the glass is cut very accurately. The separate pieces are then assembled or “laid up” then checked several times before being placed in the kiln. Once the temperature rises, there is really no going back and the firing takes its course.

At peak temperature, the glass melts; the separate pieces assume the consistency of honey and fuse together. After this occurs, the kiln is programmed to lose heat as quickly as possible to prevent the glass “devitrifying” or crystallising. Owing to the very nature of flowing liquid glass, the combined effects of heat and gravity prevail so no two pieces will ever be identical.

At about 950 F the rapid cooling stops and the annealing process begins….the glass piece is slowly and carefully cooled to 800 F. This part of the process ensures that there is no stress in the piece. Otherwise it will break.

After annealing, the kiln gradually cools to a point when it can be safely opened. This process happens very slowly, premature opening risks “thermal shock” and irreparable damage!

T o fire a piece of work, to then slump it into a mould, and to carefully anneal both processes, each piece will spend the best part of 24 hours in the kiln.