First up: Bullseye Glass is fantastic stuff. I really really mean it. With a wonderful range of colours and designs that are all compatible with each other, with lots of accessory glasses (available in almost all the colours) and types, it pretty much knocks all the others out of the park for fusing (sorry 96-ers! If they make a bigger range of stringers and frits…). But its success as a fusing glass means that it isn’t well suited for some hot glass applications.
Glass used in fusing needs to be even more compatible than in hot glass applications, because the general shape of fused pieces is flat. A large, thin, flat sheet of glass is much more susceptible to cracking from internal stresses than a round ball, or a vase. To get this incredible level of compatibility, the bullseye glass colours are relatively unsaturated when it comes to the oxides etc. that give coloured glass its colour, especially those which give opacity. Normally this isn’t an issue as the thinnest application in fusing is around 2mm, and at that thickness most of the colours are still satisfactorily vibrant.
The barrier I come up against time, and time again when I’m making murrine is that the colours dilute so much when pulled thin (because they have to have a relatively low saturation of colour to be compatible in fused applications) that they result in murrine designs that aren’t visually striking. They just look like a smudgy coloured dot. It’s incredibly frustrating, and it’s why making new mixes takes me an awfully long time. On average, for every cane that looks good enough to sell, there are three or four that weren’t. There was nothing wrong with them, but they just weren’t visually striking enough to make a good design that will stand out when fused. Maybe that’s me being a perfectionist, but I think people buy murrine from me because I spend a long time getting the designs just right. It’s the same with murrine made for lampworking, although the problems there come from the increased saturation of colours – in particular devitrification when melted/applied, or micro-bubbling of some transparent colours. Happily these aren’t issues for me with bullseye; every cane I make will at least behave properly when applied to a piece, but it might not look very good when it is!
I feel like I’m whining a lot of the time when I say this to my customers, when they ask me for a colour combination that I know won’t look very good. I’ve worked with Bullseye in the flame for long enough now that I have a library of colours that I know will keep more saturation than others when pulled, or will increase their opacity with firing. But there aren’t many of them, and they also (surprise surprise) tend to increase the stress in the final chip. They can also be a pain to work with – some get more and more viscous with increased working such that they don’t pull properly and evenly across the cane, no matter how even my heat is.
Bullseye do make some ‘opaques’ – but you’ll notice they’re labelled for use in the torch only. Increased saturation of colours = increased stress. I do use these in small amounts in my canes, but it’s a delicate balance between getting some contrast in the finished chip and managing stress. I’m almost certainly overcautious when it comes to the stress of my fused chips, but I know how horrid it is to have fused a piece with care and a stupidly long annealing time, and then for it to crack for no apparent reason a few weeks down the line, and I would hate to be responsible for that.
So anyway this long ramble is basically explaining why it takes me so long to come up with new mixes, and why I re-make my old mixes repeatedly.
Oh also – my murrine are designed for surface use. You can get away with a lot more if you’re using cane to construct the whole of a piece (like Nathan Sandberg’s work), because it’s composition is totally different from a few chips melted in to the surface. Those pieces also tend to be a bit thicker, which helps when it comes to stress too.