How Many Times Can You Fuse?

Is there a limit to how often a piece can be refused either to add on new pieces or to break up and reuse?

 

Bullseye test their glass to ensure it can go through three firings.  After that you are on your own.  This limitation has been generally accepted within the kilnforming community.

Multiple Firings

Many people report that they fire their glass many times.  I have fired Bullseye glass up to seven times using powders.  The first five firings were to contour fuse.  The final fuse firing was to full fuse.  And then there was a slump firing to make up the seven firings.  These multiple firings assume that the temperature is not taken above full fuse for any of the firings.  The annealing for each of these firings remains as for the calculated thickness of the piece.  No additional annealing time is required for multiple firings without significant changes.

You do not need to consider firing multiple process at once.  The possible number of firings is more than enough to achieve multiple processes.

High Temperature Work

However, the many firings of my piece would not have been possible with high temperatures or long soaks.  The high temperature firings are those that go to casting temperatures (835ºC/1540ºF) and above. These are temperatures for things like pattern bars, melts, and castings.  The glass can change its nature enough to give problems at these temperatures, especially with long soaks.  

If you do multiple firings at high temperatures, I recommend annealing to be from one and a half to two times the expected thickness.  And the rate of cooling will need to be in line with the length of the anneal soak.

Even with care, there can be problems.  I created a thick bowl from transparent glass, of which I was proud.  After an afternoon in the sun while on display months later it showed a crack developing.  I am still convinced - by other similar work surviving – that I annealed it properly. It exhibited minimum stress after the final flat full fuse firing. It was not checked after the slump.

Multiple firings of items with soaks at high temperatures are less likely to survive.  The number of firings possible can be determined only by experience.