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'Hard' glass (grrrr) and 'soft' glass (yes really!) - with added frit!

COE frit glass basics glass types

I feel fritty, oh so fritty...  Do you have that song stuck in your head now?  Sorry about that!  Bit of an in joke for anyone who doesn't know what 'frit' is, but it's the phrase that always comes into my head whenever a new box of colours turns up for me to play with - and that's what has happened today - just in time for the weekend!  

So what is frit?  Well, it's basically crushed glass.  It comes in different sizes and from different manufacturers and you can add things like minerals to get different chemical reactions and effects.  There are people who run businesses just from creating different combinations which people can then use in a variety of ways.  

I have to admit I'm a bit of a frit monster - I have a couple of hundred different colours and types in my workshop covering four different types of glass (yes, not all glass is created equal - and you had better know which one you are using as mixing two different types together can lead to exploding glass!).  And no, you can't tell just by looking at them - they all look like glass!  

The difference is the COE or 'coefficient of expansion' - basically how much heat it takes to melt the glass.  The most obvious example that everyone will have come across is Pyrex.  This is one of the brand names given to borosilicate glass which has a COE of 33, making it a 'hard' glass - ie. it takes a lot of heat to melt, hence it's use in kitchenware.  At the other end of the scale (the higher numbers) is 'soft' glass - this is still glass as you would expect it to look, but it takes a lot less heat to melt which often makes it easier to use in certain applications.  For those using a torch - not a furnace - beads and small pendants are often made from 'soft' glass because it's easier to shape, costs less in gas (oxygen & propane for most in the UK) and you need less expensive equipment to get going.  You can even get a starter kit and start making beads on your kitchen table for relatively little money (although be careful - this is not a cheap hobby and once you get hooked you will be selecting your next house based on your workshop requirements rather than anything else - this happened to me!)  There are also a lot more colours available in the soft glass world than in hard glass, although this is starting to change.  So why doesn't everyone use soft glass?  Well, one of the problems is that it doesn't tolerate heating and cooling as well as hard glass.  You have to keep soft glass within a small temperature range while you are working with it and get it into a kiln before it goes into thermal shock and explodes on you!  With borosilicate you can let a piece cool naturally to room temperature without a kiln and then gently heat it up again, giving you far more freedom to create bigger pieces like marbles and sculptures.

Even within the soft glass world there are different COE's from different manufacturers - I use mostly 90, 96 and 104 in my workshop but there are others available.  You can mix them to a degree but only within certain tolerances (within a few points either side of the COE) and to certain percentages or your piece will crack as it cools.  Some you can encase, some you have to use on the surface... it's all a bit like a giant science experiment - you think you know what's going to come out of the kiln but all to often you get something completely different (it's all part of the fun to be honest!)

The frit in the photos is COE96 and will be used on glass rods that are COE104, so I will need to use them sparingly to prevent cracking issues.  Why don't I just use 104 frit?  I'd love to, but there are more frits available in the 96 range than there are in the 104 range, but there are more rods available in the 104 line than there are in the 96 (and they're often more expensive).  Confused?  You should be!  If you just want to see the finished results take a look at any of the collections on the site - pretty much all of my pieces have frit on them somewhere, visible by the multiple colours on a different colour base.

If you have any questions I am more than happy to talk 'nerd' with anyone who is interested (my family have started to zone out when I start getting excited about new colour lines in particular COE's... can't think why...).  There is lots of information out there for anyone starting out or just interested in the science - you will never look at glass as just 'glass' again!

That was quite a sensible blog post for me!  No ranting or random references at all!  I'm sure I will be back to normal from next week.... until then, have a good one.  :)



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