SFSU glass had a long and illustrious 40+ year history until December 2013, when it was shut down by the university. We're all very sad, but we have been able to benefit other glass studios in the Bay Area by passing on some of the SFSU studio's equipment. Here's a list of what we donated, and a photo-inventory.
- SFSU CATS (Creative Arts Technical Services): 415-338-7758
- Campus emergency: 911
- Respirator recommendations for exposure to crystalline silica.
- NIOSH web page with links to many articles on silica related issues
"Charging the furnaces" is the overall process of melting raw glass batch to create the clear liquid we blow from. (It's also the name used for the first stage of this, where we add the new material.)
Charging is not hard, but getting the best quality glass does require some attention to getting the details right. Here's how we did it. It's an expanded version of the form we used to track charging progress.
This is the part where we add new material. The charge will take between 8 and 10 hours; it's best to start it first thing in the morning. To bring up to temperature: turn the air butterfly valve fully clockwise to get temperature to around 2300°F (~0.5-1 hr). To charge:
- Check that all the following are true (if not - wait a while):
- The temperature is right
- The existing glass is flat - no bumps or mounds [not needed for very first charge]
- The color is uniform across entire surface - no dark spots [not needed for very first charge]
- Put respirator and glove(s) on and go get bags of batch.
- Turn air butterfly valve down to lower black mark.
- Use stainless steel charging chute to gently slide bags into middle of pot.
- Add 1 bag each for charges 1 and 2.
- Add 2 bags per charge for subsequent ones.
- After charging, rake to break up bags and chunks.
- Turn air back up
- for charges 1 and 2: up to max
- for charges 3 and on: up to 1/2 way between black marks (7-8" pressure)
The new material needs time to even itself out and the large bubbles to rise and escape. This is called "fining" or "squeezing".
- Turn the air valve down to about 1/2 (7-8" pressure) for the glass to "fine"
- Leave at 2350° (no higher) overnight to cook (6 hrs min).
Cooling the furnace slowly gives time for the smaller bubbles to be re-absorbed into the liquid.
- Turn air butterfly valve down to slightly below bottom black line for "Squeeze" (4-6 hrs min)
- Let furnace cool naturally. Faster IS NOT Better
- Check for seed (small bubbles). If needed, turn down to 2.5-3 to lower temp to 2000°
- If all is good turn up to blowing temperature (~2100°).
- If both furnaces have gone out due to a power outage, then the silence in the studio is deafening.
- If the temperature readout on the controller panel is below 1800F, see if the furnace color is orange instead of the normal soft yellow - that's likely a problem.
- Make sure the blower next to the furnace/glory hole control panel is turned on.
- VERY IMPORTANT: turn the air control valve for the furnace all the way up and leave it there for a couple of minutes. (This makes sure there's no gas in the burner.)
- Plug the pedal cord we use to start the glory hole into the appropriate furnace socket. Unplugging requires a slight counter-clockwise twist and the opposite after plugging in.
- Press the pedal until you hear the pop of the restart and the soft whooshing sound of the burner.
- VERY IMPORTANT: if the sound is unusually loud or pulsating, turn off the furnace and go back to step one. This is a symptom of back-burn where the flame is not forming correctly; it causes the burner to get extremely hot, potentially damaging it.
- Adjust the air valve so the needle on the gauge is slightly above black mark, so that the furnace will come up to normal working temperature (~2100°) again gradually.
If there's a major electrical or gas shutdown, you want to trap all available heat inside the furnaces so they don't cool down too much. (That could crack the pots.)
- First: close the furnace doors. Caution: don't open them again!
- Cover the exhaust holes with frax.
- Call the instructor (Nate), plus Jim and Mike, because its unlikely that we'll all be available.
- Rig up some lights: the emergency lighting system is only godd for a short while.
- Move everything out of the way: the room gets pitch black dark and you'll bash your shins moving around in there.
- If you can trap the heat, then you've got about 2 hours to get torches and propane set up for the long haul. Don't stick torches in right away because the doors fit very well: if the exhaust holes are covered, the furnaces actually stay hot for a pretty long time - if you don't open them to peek.
- If the outage lasts longer than this, rig up some propane torches, and try to keep the temperature up.