Wednesday, 10 October 2018

Slumping Different Glasses in the Same Firing

The question has arisen as to whether it is possible to slump Bullseye and Spectrum in same slump firing.

Yes, it is possible.

But precautions are necessary.

Different temperatures are generally recommended for Spectrum and Bullseye.  Spectrum is generally expected to do the same slump as Bullseye at 25C less.

This implies that Bullseye should be put in larger or easier slump moulds than Spectrum and fired to the lower temperature required by Spectrum. The thinking behind this is that smaller spans require longer or more heat to slump.  Steeper moulds require more time and heat than less steep ones.

In general, shallow slumps will work better for both glasses together than more steep or textured ones.

To be certain of a good result, you should fire as low as practical for an extended soak.  Follow this with an extended annealing and a slower cooling rate than normal for Spectrum.

This applies to almost all the glass that is being produced with the aim of being compatible with these two glasses.  It is not possible to get a good result for float glass if it is put into the same firing as for Bullseye or Spectrum.