Feeling the Heat – Temperature Dependence of Draping Vases
One of my first exposures to fusing glass involved a very simple class where we selected 1 sheet of glass, cleaned it, figured out the center, and placed it over a form in the kiln. The instructor worked some kiln magic and after several hours invited us to peer into the kiln to see how the flat sheet of glass had begun to fall around the form. (This is technically draping and not slumping glass).
How cool! Was it really that easy to make beautiful glass vases? I didn’t know enough to realize what factors played a role in creating the magical whimsical handkerchief forms. Nevertheless, like a junkie’s first hit, I was hooked.
Yes, the instructor muttered under her breath about the danger of over-firing the glass and actually getting the mold stuck within the glass and having to destroy the glass and even the mold but who was listening? This post will not auger into disaster scenarios, though. (There is plenty of time for examples later…).
With time, I have begun to see the versatility possible with creating vases. Obviously one can fuse many pieces together to create a 2D sheet that is far more complex and exciting than a single color sheet of glass like I was first exposed to. Another Boulder artist, Bobbi Vischi (www.bobbivischi.com), takes this to an awesome level.
The key to the final shape all comes down to temperature. I have conducted a experiment creating vases that have been taken to different slump temperatures. Remember, glass most soften and begin to melt. The amount the glass ‘melts’ is temperature dependent. The glass will first seem to fold along one axis creating what is affectionately known as a ‘taco’ (or is it because this always seems to occur at lunch time during classes?). As the temperature is increased, the glass moves more and additional folds are created. At higher temps, the glass really begins to take on the form of mold it is draping over. Go much further and you are risking it all.
‘Don’t forget time!’ you may say but that seems almost secondary to the ultimate heat the glass is exposed to. At low temperatures, even if I hold for an extended period of time, I can’t seem to move much beyond the taco shape.
Pictures tell the story the best. In all cases, the kiln firing schedule was as follows:
Ramp 150F/hr to 300F and Hold for 15 minutes
Ramp 300F/hr to 1100F and Hold for 20 minutes
Ramp 150F/hr to SLUMP TEMP and Hold for X minutes
Cool 400F/hr to 950F and Hold for 1 hour
Cool 150F/hr to 800 and Hold for 10 minutes
Example 3: 1225F for 1 min (about as far as want to go)
Now back to experimenting with my vases….