You’re probably aware that murrine chips placed on the surface of fused glass change their appearance dramatically between cold and fully fused. In many glass applications, murrine are designed to be seen in cross-section, for example the ubiquitous millefiori paperweights from Murano and vitrigraph platters and bowls made popular by Nathan Sandberg

However, chips placed on the surface of a glass piece distort because of the 6mm rule. As y’all know, the surface tension of glass means that it wants to be ~6mm thick.  So, if you put something in the kiln that has less mass than a ~6mm diameter sphere of glass (about 0.2-0.3g), it is going to turn into the nearest thing to a 6mm sphere it can, to minimise surface tension (see also: frit balls).

So, a little murrine chip sitting happily on the surface of 2 x 3mm layers of glass going in for a full fuse will begin to round up according to the 6mm rule.  But, because the chip is sitting on top of glass which is ALSO melting, it won’t form a little ball but a hemisphere, because the bottom of the chip became ‘sticky’ at the tack fuse temperature, and became attached to the base glass before the surface tension started to change it’s shape.

“This is all very nice Kathy but are you eventually going to make a point?”

Yes! That is – I specifically design my murrine to work WITH this process.  I aim for the fully-fused result, rather than concentrating on a complex cross-section.  This is why I do not bother making novelty-style stars, snowflakes, hearts, badgers, whatevers.  In my opinion, the fully fused chip will never, EVER look like the cold chip, and frankly, the effort required to make them very rarely pays off.  Yes, yes, I know, you can tack fuse them, and they’ll look like the cold chips.  Well done smarty pants.  The other reason I don’t make them is that they’re just not my style 😉

So, when you full-fuse, the distortion I’ve been talking about means that most of what you end up seeing is the OUTSIDE of the cold chip.  The pictures on the left show cross-sections of fused chips at different temperatures.  You can see how the internal structure of the chips start to distort and bend, resulting in the very different appearance from cold to full fused chip.

Some of the more eagle-eyed of you might have noticed that I often cut some styles of chip taller than others. This is because the height of a chip also affects how much of the inside you see. I am not sure why this is, but my gut hunch is that it’s something to do with the relative strength of the surface of the glass below the chip versus the amount a chip wants to ‘ball up’. So, a taller chip has a larger surface area that wants to round up relative to a shallow one. Maybe. Either way, the taller a chip is, the more of the outside you see in the final result. Which is why I cut the swirly chips a little taller than the ‘doubles’ (where there’s a stringer design on an inside layer too). Because I want the final fused chip to show more of the outside relative to the inside.

Left – cold. Right – fully fused. Notice how little area the inside pattern of the cold chip takes up, and how the majority of the design comes from the outside of the chip.

When I design a chip, I start from the OUTSIDE and work IN. Because, as I’ve been labouring to tell you, the outside is the feature of fully-fused murrine chips. There is very little point me making a beautiful centre to a chip and then putting a plain colour around the outside. All you will end up with is a plain blob with that beautiful centre shrunk into less than 40% of the visible chip. I often know what I want the outsides of the four chips in a mix to look like before I start thinking about the middles. A good chip has a beautiful (and NEAT, gotta be neat and symmetrical!) outside, with a pattern inside that compliments and balances it. It is not as easy as it sounds, I usually draft out my mixes on paper or on my iPad before I start (felt pens = £, glass = ££££). There’s also the matter, which I’ll talk about in a subsequent article, that a bullseye colour pulled thin (< 0.5mm) can look very different to the standard 2 or 3mm glass.

So, now you know about how I use the way murrine fuses to design chips that look beautiful in full fused applications. Thanks so much for reading till the end!

Is there something you’d like to ask me about my murrine or process, or want to know more about, do just send me an email! I love talking about glass =)