This post has been in my head for a long time, and might explain a lot to people who might be wondering why I don’t make more flower and star murrini…

In flamework and furnace-glass, the glassworker is able to (attempt to…) control the way that murrini melt in to the base glass, by touching the chip gently using a tool.  This means they can make it open-centre (showing a detailed centre design) or closed-centre (poking it closed and letting the outer layers of design be the feature).  By contrast, in warm glass applications, you can’t normally touch the murrini while they are melting into the base glass, unless you want to burn your hands off. As a result, fusing with murrini is a different process, and different considerations should be made when designing pieces, to get the best effect from your little chips.

Poked centre murrini on a bead

Poked centre murrini on a bead

Unpoked Murrini on a bead

Unpoked murrini on a bead

A lot of balls.

Yes, indeed.  The main problem is the famous ‘6mm rule’ – the surface tension of glass means that it wants to be (about) 6mm thick.  So, if you put something in the kiln that has less mass than a 6mm diameter sphere of glass (about 0.3 grams), it is going to turn into the nearest thing to a 6mm sphere it can, to minimise surface tension.  Fusers use this to great effect in the creation of frit balls.  However, the most pleasing aspect of your little murrini chip is it’s surface design, which is flat, and so it’s not ideal if the chip curls up into a little ball, as this will distort the pretty design!

I did some experiments to see what happens to a murrini chip through a standard full-fuse cycle:

Tack fused murrini flower

Tack fused murrini flower, showing minimal distortion of design

Fused to 765 - low full

A cross section of a murrini chip fused to a low full fuse (about 745) and held for 10 minutes. Note how the thickness of the centre white section is smaller at the top than at the bottom – the surface has begun rounding-up and distorting the design.

A cross section through a flower murrini chip

A cross section through a flower murrini chip full fused into the base glass. Note the much smaller width of the centre orange at the top compared to the base of the chip (the original dimensions.

Bottom of flower chip, showing original design

Bottom of flower chip, showing original design (through the bottom of the tekta glass)

Top of the murrini chip

Top of the murrini chip – you can see the original design in the very centre.

 

I drew a little cartoon to visualise what is happening at the various stages in the process:

 

Murrini Melti

So, what can we do about it?  The whole idea of murrini is that you can have lots of intricate details in your fused pieces that you’d not normally be able to manage (without some crazy skills and/or dedication).

There are a few ways around this problem:

  1. We can design the cane such that it’s still pretty even when it rounds up into a little ball.
  2. We can try to stop the murrini turning into a little ball in the first place.

Option 1 – Altering the Cane Design

This is the easier of the two options.  Basically, you acknowledge that you are unlikely to see much of your centre design in your final full-fused piece, but you get SUPER CREATIVE with the outside.  Layered lines, swirls, twists, you name it.

Unfused chip (note boring middle)

Unfused chip (note boring middle)

Same chip fully fused

Same chip fully fused

This is fine, but it means that things like stars and flowers are off the cards. So, the second option is:

Option 2 – Trying to stop the murrini turning into a little ball in the first place.

You can do this several ways (these are just the ones I’ve tried… I’d love to hear if you have others!).  The first way is to reduce the volume of the chip by cutting it thinner.  I’m not sure exactly why this works,  my current theory is that, because the bottom of the chip ‘sticks’ to the surface of the base glass at tack fuse temperatures, the tension of the base glass stops the thinner chip from balling up.  With a taller chip, there’s more glass in the chip, so the surface tension of the chip wins.  Or something.

The easier option is to fuse the chip UNDERNEATH your base glass.  This is fine but can have limitations for your design, or might require you to pre-fuse your top layer.  In my tests, I’ve noticed that some chips show higher stress when they’re fused beneath rather than on top base glass, but some are the other way around.  I’m still trying to investigate why this might be, so watch this space…

The difference in the final result between fusing your chip on top or underneath is profound, though.  The weight of the glass on top stops the balling up process at the beginning, meaning you see much more of your lovely surface design.

On top versus underneath

The difference between being on top or underneath (*snigger*)

So, this works well for our flowers and stars!  Observe:

Star murrini fused beneath of base glass

Star murrini fused beneath base glass – star shapes!

Star murrini fused on top of base glass

Star murrini fused on top of base glass… less star, more… blob (sorry for the appalling picture…)

I realise I’ve waxed lyrical about this for some length, now. Congrats if you’re still reading! But, I thought it was worth sharing my findings about using murrini in fusing and their limitations. I really hope it was helpful =)