Misty Cherie ~ Glass Artist

LAMPWORKING

History

Lampworking is glassworking using a torch to melt and shape the glass. Although the art form has been practiced since ancient times, it flowered in Murano, Italy in the 1300s, and spread from there to the rest of Europe.

In addition to artwork, lampworking is used to create scientific tools, particularly for chemistry.

Early lampworking was done in the flame of an oil lamp, with the artist blowing air into the flame through a pipe. Most artists today use torches that burn either propane or natural gas for the fuel gas, with either air or pure oxygen as the oxidizer.

Types of glass

Lampworking can be done with many types of glass, but the most common are soda-lime glass, sometimes called "soft glass", or Moretti after an early Italian manufacturer; and borosilicate glass, particularly Pyrex. Leaded glass tubing was commonly used in the manufacture of neon signs, although its use has been fading due to environmental concerns and health risks.

Different colors of glass must be carefully selected for compatibility with each other, both chemically and in terms of coefficient of thermal expansion (COE). Glass with incompatible COE, mixed together, can create powerful stresses within a finished piece as it cools, cracking or even violently shattering the piece. Different major types of glass, e.g., borosilicate and Moretti, are not compatible with each other. Chemically, some colors can react with each other when melted together, usually causing undesirable effects such as discoloration, bubbling, or devitrification.

Borosilicate glass is considered more forgiving to work with, as its lower COE makes it less apt to crack than Moretti. However, it has a narrower working temperature range than Moretti, has fewer available colors, and is considerably more expensive. Also, its working range is at higher temperatures than Moretti, requiring larger torches and the use of oxygen instead of air. In addition to producing a hotter flame, the use of pure oxygen allows more control over the flame's oxidizing or reducing properties, which is necessary because some coloring chemicals in borosilicate glass react with any remaining oxygen in the flame either to produce the desired final color or to discolor if extra oxygen is present.

Tools

Tools for lampworking are similar to those used in glassblowing. Graphite or steel pads, rods, and other shapes are used for marvering the glass. Brass, graphite, or wooden molds (usually of apple or cherry wood) can be used to mold the hot glass. Tungsten picks can be used to drag glass around on the surface, or to bore a hole through a piece. Steel jacks, usually coated with beeswax, are used to neck down or cut off a piece.

Technique

After designing a piece, a lampworker must carefully plan how to construct it. Once ready to begin, the lampworker slowly introduces glass rod and tubing into the flame so that the pieces won't shatter from thermal shock. The glass is heated until molten, merged with other pieces, and shaped with various tools. All parts of the workpiece must be kept hot, at similar temperatures, or else they can crack or shatter. Once finished, the piece must be annealed in an oven, or else it will eventually crack or shatter.

Annealing

Annealing, in glass terms, is heating a piece until its temperature reaches a stress-relief point, that is, a temperature at which the glass is still too hard to deform, but is soft enough for internal stresses to ease. The piece is then allowed to heat-soak until its temperature is even throughout; the time necessary for this varies depending on the type of glass and thickness of the thickest section. The piece is then slowly cooled at a predetermined rate until its temperature is below a critical point, at which it can no longer generate internal stresses, and then the temperature can safely be dropped to room temperature. This relieves the internal stresses, resulting in a piece which should last for many years. Glass which has not been annealed will usually at least crack, and can shatter due to a seemingly minor temperature change or other shock.

This article is licensed under the GNU Free Documentation License.

It uses material from the Wikipedia article "Lampworking".