Adventures in COE's???

I took this picture to show  how I keep my glass rod organized.  The glass rod is what I use to make my lampwork beads.  The round white things you see in this picture are pieces of PVC pipe.  It works great for holding glass rods!  I used a hacksaw and cut the pipes into lengths long enough to hold the rods.  I also pull the glass out of the pipe a little bit so that I can see the color of the rod easily.

I try to keep my glass organized.  It doesn't always work.  I use a few different types of glass, including glass that has different COE's.   COE is very a very important part of working with hot glass.  It means,  Coefficient of Expansion.  The lower the COE, the harder the glass and the higher the temperature is needed for it to begin melting.  

When melting glasses together, either when fusing or lampworking, it is very important to make sure that the glasses used are compatible.  That means that the glasses should have the same COE.  The term COE basically means, how fast or how slow the glass heats up and cools down. That means, if you accidentally used glasses with different COE's it is very possible that when the piece cools down in a kiln, it will develop stress cracks which will inevitably break the finished piece.  That happens because the pieces are not cooling down at the same rate!  And unfortunately, that will produce cracks.  

When buying sheet glass,  many companies will put labels on their glass stating the COE.  When buying sheet glass that is not marked, a sample fuse is very important to test compatibility before creating a project.  Usually sheets of glass made by the same manufacturer are not even compatible!   Many manufacturers make sheet glass specifically for fusing, and it is these sheets of glass that are marked with COE's.  COE's are shown as numbers, just keep the numbers together and you'll be ok!

There are also a few different types of glass rod for lampworking.  It is important to use compatible glass rod too!   There are also two distinct types of glass rod, soft glass and (borosilicate) boro glass. Never mix soft glass and boro glass.  Soft glass rod comes in a few different COE's and they should not be mixed either!  Although,  it is possible to mix small amounts of soft glass that doesn't have the same COE's but it should not be too much, or there is the usual possibility of the piece breaking!

Below is a sample of a Bullseye COE label that you'd find on a sheet of their fusing glass.