Wednesday, 18 February 2015

Lampworker's vocabulary: glass (P.1)

I've already told you a little bit about lampwork in general, however it's only a beginning of stories about this type of glasswork, myself, my work and pieces. Also known as flameworking or torchworking, as in the modern days we do not use oil-fueled lamps any more like lampworkers did before, lampworking is too versatile to sum everything up about it in only one short post. So today I'd like to tell you about the glass I and other lampworkers use - soft (or soda lime) glass.

Generally speaking, glass is a mixture of silica and oxides. Depending on the type of oxides - soda and lime, borax, lead - it can require lower or higher temperature to be molten and worked with. To be honest, lampworking, as well as other types of glass work, can be done with many types of glass, including recycled. One of the most popular and also widely used by the lampworkers is borosilicate glass, often called hard glass. However, as I don't work with it, I have nothing to tell you, at least so far ;) 

Soft glass is more commonly used for lampworking because it melts at lower temperatures and more liquid at the molted stage. It also has a wide palette of colors, since various metal oxides added to the clear glass can impart it different tones. For example, chromium creates green colors, cobalt is used for blue, nickel for violet and brown tones, and selenium metal for red (you can read more about glass coloring here). This gives more opportunities for beadmaking. At the same time, soft glass expands a lot more and contracts more when cooled, and more prone to cracking due to thermal shock, so it requires some experience to work with.

There are several glass manufacturers on the market (I'll tell about them in one of other posts), and each use its own formulas. However, the only thing that actually matters is whether types of glass from different sources are compatible when combined with each other or not. First of all, this means that the coefficient of expansion (COE) - a degree to which glass (or other material) expands and contracts at a fixed range of temperature - has to be the same for all types of glass to be used in one piece of work. The COE for soft glass ranges from 89 to 109, however lampworkers use glass with COE 104 (mostly) or 96. In some cases different types of glass with the same COE, even from one manufacturer can still lead to a bad result when used wrongly though.

Glass color remain more or less stable (there are exceptions, of course) after heating, forming and shaping with tools and hand movements, annealing and cooling one-color bead. However, different oxides in each glass color can react with one another in molten state and create third color or tone effects. Moreover, there are couple types of glass that strike their color or change colors from one to another during the processes of reduction, reaction and overheating only. Metals like silver, copper and gold, applied to or fumed into the glass surface can change its color as well.

Knowing abilities and possibilities of glass is a first step to masterpiece ;)
To take a look at, purchase and order items made in the lampwork technique, please, visit my Etsy store.