Will these directions produce a properly fused, round blank?

[Shelley Lewis]

I downloaded this project from a very popular glass website:

Use a 3mm 12" clear system 96 circle, then place a 3mm 9" transparent colored circle in the center. Full fuse using following schedule:

250 250 30
250 1050 60
200 1250 30
250 1370 20
300 1465 10
Full 950 60
200 800 10
300 100 0

I'm fairly new to fusing, but it's my understanding that glass wants to be 6mm thick. If both layers are 3mm thick, won't the clear glass pull in, causing an uneven finished circle?

[JestersBaubles]

It will likely pull in fairly uniformly, if both pieces are nice, uniform circles, and if the 9" disk is placed in the middle.

My schedule would be different, but firing schedules really aren't the issue here.

Dana W.

[JestersBaubles]

Your schedule:
250 250 30
250 1050 60
200 1250 30
250 1370 20
300 1465 10
Full 950 60
200 800 10
300 100 0

What I typically use:
250 > 1100, hold 30
50 > 1250, hold 30 - 60 (for the bubble squeeze)
250 > 1460 (or whatever works in your kiln for full fuse) 10-20, depending upon the piece
Full > 950, hold 60 to 90, depending upon how much I like the piece
100 > 700, hold 5 or 10
Off (my kilns are fiber brick and cool VERY slowly, so this is a safe schedule for me)

Dana W.

[David Jenkins]

Interesting thought experiment. I'd like to see actual results. Then some results with varying diameter ratios.

[Bert Weiss]

Your schedule:
250 250 30
250 1050 60
200 1250 30
250 1370 20
300 1465 10
Full 950 60
200 800 10
300 100 0

What I typically use:
250 > 1100, hold 30
50 > 1250, hold 30 - 60 (for the bubble squeeze)
250 > 1460 (or whatever works in your kiln for full fuse) 10-20, depending upon the piece
Full > 950, hold 60 to 90, depending upon how much I like the piece
100 > 700, hold 5 or 10
Off (my kilns are fiber brick and cool VERY slowly, so this is a safe schedule for me)

Dana W.

Dana, I think your long hold at 950 is too hot. I would suggest 920. For thicker pieces, Bullseye says 900. Your anneal is actually happening on the next segment, whereas if you soaked lower, it would be happening there as well.

If your piece is placed close to a wall of the kiln, the longer you hold, the more likely you are to introduce a temperature gradient in to the glass. Once this gradient is greater than 10ºF, the glass can not anneal.

[Brad Walker]

I think your long hold at 950 is too hot. I would suggest 920.

They're using System 96. Spectrum's recommended annealing temp is 950.

[Bert Weiss]

I think your long hold at 950 is too hot. I would suggest 920.

They're using System 96. Spectrum's recommended annealing temp is 950.

Maybe, but for all intents and purposes both glasses anneal about the same, according to my understanding.

[JestersBaubles]

I think your long hold at 950 is too hot. I would suggest 920.

They're using System 96. Spectrum's recommended annealing temp is 950.

Maybe, but for all intents and purposes both glasses anneal about the same, according to my understanding.

I use Sys 96 and anneal everything at 950 (their recommendation). I will keep your comments in mind, and if I start having issues, I'll rethink it .

Thanks, Daan

[Barry Kaiser]

Little bit of a topic drift, but Bullseyes change to anneal hold at 900 still has me scratching my head.
The glass did not change.....they used 960 for 20 years. Were they suggesting the wrong temperature for 20 years.
Not that it makes a huge difference.

Barry

[Brad Walker]

Little bit of a topic drift, but Bullseyes change to anneal hold at 900 still has me scratching my head.
The glass did not change.....they used 960 for 20 years. Were they suggesting the wrong temperature for 20 years.
Not that it makes a huge difference.

The only place it makes a huge difference is when annealing a really thick piece, where annealing at 900 can save you hours or even days. Aside from that, in my experience it doesn't matter if you anneal at 960, 950, 900, or anywhere in between.

[Bert Weiss]

The removal of stress takes place in about 15 seconds, when the entire mass of glass is sitting within the anneal zone and is within 5ºC throughout the mass of glass. In general, this happens easier at the bottom of the anneal range than at the top.

The anneal strategies that stop at 960 or there about are designed to stabilize the temperature at the high end, and then ramp it down through the range. The strategy of soaking lower accomplishes the same thing in a different way. Yes, for thicker pieces this makes more sense.

I learned about all this when I asked Dan S. and Ray A. to comment on the difference between the anneal strategy I was using for float, which involves a long soak at 1000 and the same amount of time going down to 900, as opposed to Stone's schedules which soak at 1030 for a short time and then ramp down to 900. We were taking about the same amount of time, but spending it at different temperatures. They told me my approach was the better of the 2. Several years later, they changed the Bullseye recommendations. BTW, float anneals about 80ºF hotter than Bullseye or Spectrum.

Barry works with pieces about 1" across. These are easier to stabilize at a temperature throughout the piece than larger masses of glass, making the anneal challenge much easier.

[Jerrwel]

I downloaded this project from a very popular glass website:

Use a 3mm 12" clear system 96 circle, then place a 3mm 9" transparent colored circle in the center. Full fuse using following schedule:

250 250 30
250 1050 60
200 1250 30
250 1370 20
300 1465 10
Full 950 60
200 800 10
300 100 0

I'm fairly new to fusing, but it's my understanding that glass wants to be 6mm thick. If both layers are 3mm thick, won't the clear glass pull in, causing an uneven finished circle?

OK, I'm going way off topic, however this relates to not only creating the blank but subsequent firings as well. According to Stone http://www.warmglass.org/books/books/126-fsg, the greater issue in this layup is not the single layer of glass but the inconsistent thickness of the project (Stone, page 27). The heating phase scheduled is well within Stone's 5/16-thickness schedule (moving to the next thicker schedule or two is how he compensates for risk of added issues); however, Stone's anneal temperatures are much, much lower. Even Randy & Carole Wardell who introduce single layer fusing in their book 'Joy of Fusing,' use a single annealing phase rate of 125F/hour.

My recent firings for projects having similar layups have been taking 16 hours and longer; some of this time is related to my kiln cooling naturally more slowly than the program rate below 800F but the lower anneal rates (Stone) do add several hours to the firing compared to the schedules discussed here and even the Wardells' annealing temp of 125F. I'd like to reduce the time for these firings.

Have Stone's annealing temps been found to be too conservative? I'll be working with this later, but want to keep variables limited at this time as I experiment with single layer elements in projects.

[Morganica]

The 3mm 8" transparent circle will stabilize the center of the piece. The 3mm edges will want to pull in, starting from the outermost edge, so you'll get a "lip" around the edge of the piece and it will be slightly thinner right behind it. If you don't overdo the processing, it's a nice way to finish off the edge of a piece--I do that quite a bit.

If you do overdo the processing, you'll start to get holes in the 3mm space, probably around .75" in from the edge. But that's going to take awhile.

The holds at 250, 1050, 1370, 800, 700 are pretty much a waste of time--if you must put in a hold to avoid thermal shock before about 1150-1200, the ramp is too fast--and a 300-degree downramp is probably not going to happen much past 500-600 degree in a closed kiln, even if it's fiber, so that part of the schedule is mostly fiction.

Of course, the "when in doubt add a hold" notion is pretty pervasive. I don't guess it hurts much. I've found that people tend to stick with whatever maxims they started out with, even when the piece fails. So if someone wants to add a 30 minute hold at 250, or a 10 minute hold at 700, well...it's your time to waste.

I was at the BeCON where they announced the 900F annealing soak change, and the reasons stated at the conference were primarily as Brad said, i.e., to improve stability and save time on thicker projects. It works perfectly well for thick or thin fused pieces, at least in my own testing, and it's less about "removal of stress" than it is about preventing the introduction of stress. In casting, where you have a fully 3-dimensional piece without an obvious point for "thickness" measurements, it's a real advantage.

Jerrwel, I don't think Stone's tables are too conservative but it's a matter of degree (heh-heh). The amount of variability in thickness, relative to the size of the piece, as well as the overall symmetry, are important. In this case, we've got two circles--the most stable flat layup--and at no point do we exceed 6mm of glass. There actually is very little variability here.

The trick with single-layer projects is to give yourself an extra inch or so of edge and watch processing times on every fuse firing. Once you start lower-temperature firings (such as a slump), you trim the piece to the real size.

[Jerrwel]

Jerrwel, I don't think Stone's tables are too conservative but it's a matter of degree (heh-heh). The amount of variability in thickness, relative to the size of the piece, as well as the overall symmetry, are important. In this case, we've got two circles--the most stable flat layup--and at no point do we exceed 6mm of glass. There actually is very little variability here.

The trick with single-layer projects is to give yourself an extra inch or so of edge and watch processing times on every fuse firing. Once you start lower-temperature firings (such as a slump), you trim the piece to the real size.

Cynthia, thanks for this insight; it makes real sense that the circles are more stable and the layup does have little variability. I believe by firing no higher than 1425F I also avoid a lot of the 1/4" rule-related stress as the glass viscosity is minimalized while the rounded, raised edge is still developed. Thanks,

[Morganica]

Cynthia, thanks for this insight; it makes real sense that the circles are more stable and the layup does have little variability. I believe by firing no higher than 1425F I also avoid a lot of the 1/4" rule-related stress as the glass viscosity is minimalized while the rounded, raised edge is still developed. Thanks,

Well, don't count on that last always being true--the longer the glass sits at a processing temperature, the more molecular bonds will break, and the more reduction in viscosity (to a point, anyway). (More viscous=thicker, less viscous=runnier)

[ncbill]

Little bit of a topic drift, but Bullseyes change to anneal hold at 900 still has me scratching my head.
The glass did not change.....they used 960 for 20 years. Were they suggesting the wrong temperature for 20 years.
Not that it makes a huge difference.

The only place it makes a huge difference is when annealing a really thick piece, where annealing at 900 can save you hours or even days. Aside from that, in my experience it doesn't matter if you anneal at 960, 950, 900, or anywhere in between.

Brad, I don't understand how annealing at 900 can save time (or did you mean annealing at 960 can save time?) Annealing occurs faster at a higher temperature because the viscosity is lower. Of course, if one anneals at 960 and then doesn't ramp slowly to 900, new stresses could be introduced, necessitating another soak at 900. If I'm not wrong, the time to anneal depends upon the temperature and the size of the object - the safe cooling rate depends almost entirely on the size of the object

[Morganica]

Little bit of a topic drift, but Bullseyes change to anneal hold at 900 still has me scratching my head.
The glass did not change.....they used 960 for 20 years. Were they suggesting the wrong temperature for 20 years.
Not that it makes a huge difference.

The only place it makes a huge difference is when annealing a really thick piece, where annealing at 900 can save you hours or even days. Aside from that, in my experience it doesn't matter if you anneal at 960, 950, 900, or anywhere in between.

Brad, I don't understand how annealing at 900 can save time (or did you mean annealing at 960 can save time?) Annealing occurs faster at a higher temperature because the viscosity is lower. Of course, if one anneals at 960 and then doesn't ramp slowly to 900, new stresses could be introduced, necessitating another soak at 900. If I'm not wrong, the time to anneal depends upon the temperature and the size of the object - the safe cooling rate depends almost entirely on the size of the object

900 and 960 aren't magical numbers; annealing can take place anywhere along that range. You could anneal at 920 or 940, too. The time savings you get from the lower anneal soak is mostly because you eliminate 60 degrees of initial anneal cooling, not because the anneal soak is inherently faster or slower.

If your initial anneal cool is only 5 degrees per hour, starting that cool at 900 instead of 960 lets you drop quickly from process temp to 900 and saves nearly 12 hours of kiln time. Obviously, the faster the initial anneal cool (i.e., the thinner the glass you're cooling), the less time you'll save, so 900 degree anneals primarily save time for artists making thicker work.

I don't think it's accurate to say that "the safe cooling rate depends almost entirely on the size of the object." It depends on the ratio of surface area to total volume, the relative viscosity of the glasses involved and the shape of the piece. The object of the game is to cool all parts of the glass at the same rate, to prevent one area from contracting faster than another and introducing stress where those areas meet.

Glass is a lousy conductor of heat, so the longer the distance between surfaces (thickness), the slower you must go to ensure that heat is leaving the center as fast as it does on the surface. And some shapes simply contract more evenly than others.

So...you can anneal a 4-inch sphere of clear glass more quickly than a box with 4-inch walls, and a 1/4-inch thick black and white glass chessboard will probably need more anneal time than a 1/4 inch thick piece of solid black. And a kneeling figure with thin, outstretched arms is gonna be a real pain to anneal. (ask me how I know this)

[jim simmons]

with thin, outstretched arms is gonna be a real pain to anneal. (ask me how I know this)[/quote]

Ok, how do you know this? :>)
Jim

[DonMcClennen]

I don't think the single layer 1 1/2" rim is a good idea. You'll get pull in and maybe needles at edge. Both layers same dia. will give much more controlled results.

[Bert Weiss]

I have been taught that glass loses it's stress quicker at the lower end of the anneal range than in the upper area. Cynthia's point is good about the total time factor.