Friday, November 8, 2013

Glass Notes - tack fuse

I had some tack fusing to do to stick some dots onto a background. I have only done this a few times and I decided not to go with the hotter temp at the last minute because you can't fix something that s melted too much and I just chickened out. I had notes on it but not enough experience.
The pieces are stuck but I wanted them to melt a bit more onto the background. I am trying to make some little Christmas buttons for the Glass Applique shop and dotty pendants to match my shirt fabrics.

These were done on:
ramp 1 - 200 rate, 600 temp, 30 mins hold
ramp 2 - 350 rate, 760 temp, 5 mins hold
ramp 3 - full rate, 500 temp, 15 mins hold
ramp 4 - 350 rate, 370 temp, 0 hold

I am concerned that 780 C will be a bit too hot but I don't know if 770 C will be hot enough. I have worked out from researching that the glass softens a lot between 760 and 780 and melts at 804. Does it melt at 800 too? So much experimenting left to do.

From my notebook:
Based on Bullseye tech notes.
A rate of 222 is conservative initial heating rate.
Need to heat to 540 C or 600 C and hold to make sure all the glass is over 454 C. Up to 454 C the glass can undergo thermal shock.

Ramp 1 -  200 rate, 600 temp, 30 min hold (bubble squeeze and temp equalising stage)
Ramp 2 - 350 rate, 760 or 780 or 800 temp, 5 or 10 min holds (forming stage)

The second ramp needs to be fairly rapid to take the glass through the crystal forming stage which starts at about  730 C but not so fast as to form bubbles.

After forming you need a rapid cool to prevent crystals forming.

Ramp 3 -  Full rate, 500, 15 mins hold (equalising temp)

The soak or hold time for ramp 3 depends on the size and thickness of the pieces. Pendants I will soak for 15 mins, a 2 layer coaster for 30 mins and a 3 layer coaster for 45 mins.

Larger pieces  like coasters need two more cooling steps. Slower rate of 220 down to 427 C  and hold for 10 mins (ramp 4) then a bit faster rate of 350 down to 370 C and 0 hold (ramp 5).

For pendants and buttons only one final cool.

Ramp 4 - 350 rate, 370 temp, 0 hold


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