Northstar annealing recommendations

[Tanya]

I was checking out Northstar's site and happened across their annealing chart:

Borosilicate Annealing
Anneal Time: 1 hour for every 0.25 inches of piece thickness
Soak Time @ A/T – 125 deg: 50% of the Anneal Time for pieces 0.25 inches thick or
less. 100% of the anneal time for pieces greater the 0.25 inches thick
Soak Time @ A/T – 200 deg: 25% of the Anneal Time
Soak Time @ A/T – 350 deg: 25% of the Anneal Time
Soak Time @ A/T – 550 deg: 25% of the Anneal Time
A/T=Annealing temp, degrees F

This is a lot different than Bandu Dunham's recommendations. I understand that the high metal content of the glass could increase soak time over clear boro, but does it increase it this much? Using this schedule, a 1" bead would soak for 4 hours, ramp down to 925 and soak for 4 hours, ramp down to 850 and soak for 1 hour and so on. This would be a total ramp down time of 7 hours to 500 deg on top of a soak time of 4 hours for a total of 11 hours :shock:

I thought a soak time of an hour would be more than sufficient for a 1" bead. Then, ramping down to 950 deg at 70-100 degrees an hour. Then, the cooling rate can increase a bit with no further soak periods. Since I rarely make anything as large as 1", I've always thought this was reasonable.

Does anyone have any suggestions? How long do you anneal boro beads, say 1" thick or less?

[alexm]

I anneal my boro at 1050F for 1 hour for beads 1" or less in diameter. Then I ramp down to 700F at 150 degrees/hr, then I turn the kiln off.

[Tanya]

Thanks Alex. That sounds more like it!

[Mr. Smiley]

Northstars numbers are not out of line at all. The slower you go, the better. I don't see soaking at any point under 950 doing any good, but whatever makes you warm and fuzzy. I'll need to chat with NS and find out why they suggest this. Going slow from annealing temp to strain point is most important. When I make toys, I am on a 24 hour annealing schedule bare minimum. Thicker pieces are longer... that's just the way it goes. Look up annealing and read everything you can on it. You'll understand that just because it doesn't break, doesn't mean it's free of stress or annealed properly. ;)

[Tanya]

Hi Smiley - I do like to be safe on the annealing side. I've read a fair amount about annealing - the most thorough treatment I've read is in Bandu Dunham's Contemporay Lampworking. I'm confused because the tables in CL list VERY different soak times. Also, his recommendations don't include long soak times at the strain point or below. I'm interested to hear why NS recommends these long soak times, especially the ones at 925 (assuming one is annealing at 1050) and below. Thanks!

[Mr. Smiley]

I'll call Charles and chat with him about that soon. No idea why anyone would soak at those temps. On a thick piece, I can see going slow below the strain point, just to avoid thermal shock... but not soaking. I agree that it is weird... really weird. There may be some crazy reason that makes total sense though. :lol:

[Tanya]

Thanks Smiley! Meanwhile, I'll increase my initial soak time a bit. After all, I really do want to practice safe soak...

[Mr. Smiley]

Soak longer than you think and ramp slower than most people say to. ;)