Pattern Bar Work - Annealing Advice

[Lynn Holman]

Hello. I've been working with pattern bars for a short while and am having problems incorporating them into larger work. So far, I've been able to adjust the schedule but now I'm at a point where I could use some advice. So, if you anything you can share would be appreciated.

Annealing break. Spectrum glass. 2 layers of 3mm plus 1 layer 2mm, pattern bar slices are 1/4" thick with 2 mm clear on top. Size is 16". Kiln interior is 18", Paragon Pearl with elements on top.

Schedule:
125>480>0
200>1150>30
50>1240>30
800>1450>10
9999>950>1.30
55>860>10
100>660>10
Cool to room temperature.

Note: the cracks are right between the adjoining pattern bars. I've had this problem before on smaller pieces and have been able to adjust the schedule, which is how I got to the above.

Thanks in advance for the help!

[carol carson]

Where did you get your schedule?

Schedule:
125>480>0 - Why 480°?
200>1150>30 - Why the change from 125° to 200°? 30 minutes is not nearly long enough for your thickness.
50>1240>30 - Why the slow down in your ramp up (50°)? Again, why the 1240° hold?
800>1450>10 - this should be AFAP (As Fast As Possible)
9999>950>1.30
55>860>10
100>660>10 - Why the speed up?
Cool to room temperature.

[Laurie Spray]

I would have taken this.....

100 / 800 no hold
250 to 1150 hold 45
50 /1250 hold 45 (not real clear on the set up.....but this is for bubble squeeze)
350 to 1450
9999 to 950. Hold 3 hrs
100 to 850 hold 60
100 to 700 and off

I am sure others would have other thoughts but this works for me and we do alot of pattern bars.
Shame......it is a beautiful piece. At least there is lots there you can salvage.....

[JestersBaubles]

Where did you get your schedule?

Schedule:
125>480>0 - Why 480°?
200>1150>30 - Why the change from 125° to 200°? 30 minutes is not nearly long enough for your thickness.
50>1240>30 - Why the slow down in your ramp up (50°)? Again, why the 1240° hold?
800>1450>10 - this should be AFAP (As Fast As Possible)
9999>950>1.30
55>860>10
100>660>10 - Why the speed up?
Cool to room temperature.

I disagree. I would slow down on the way to 1450, and 1 hr 30 isn't long enough for annealing that size of a piece. The slow down to 1240 and hold is a typical bubble squeeze.

Dana W.

[Brock]

. . . 1 hr 30 isn't long enough for annealing that size of a piece.

Size? You anneal for thickness, not size.

[Lynn Holman]

Thanks everyone for your responses.

Carol, most of the schedule is from Graham Stone's book and here's the rationale for those that are:
125>480 This is to prevent thermal shock. I typically flip and fire and have had a pattern bar piece break and then fuse together but have not had this since I added this.
100>660 10 The speed up is based on the schedule in Graham Stone's book about being able to increase the rate of cooling after 860 based on the thickness.
The 2nd and 3rd steps (200>1150 30, 50 1240 30 are the bubble squeezes) as I have a 16" piece of clear over the top. This is because I am limited on shelf size and can't dam the piece and the bars are tighter when there's glass on top and the glass helps fill the gaps as the bars don't completely butt up against each other from rounded corners. I'm experimenting with cutting thicker slices to avoid having to cap it.

[Laurie Spray]

on a piece that you really care about......(of course that is most pieces for most of us!) the 100 an hour to 800 is an insurance policy. i have found that around 800 is the top of the "cracking stage" from thermal shock. 480 is better than nothing and may do it although I am more safe and not sorry.

did it happen on the way up or down........sharp edges or fire polished?

[Lynn Holman]

Thanks, Laurie. The crack happened on the way down. Edges are sharp.

[Laurie Spray]

I think it is due to the uneven thickness in your piece and did happen on the way did.......

all I can tell you is I do work like this a lot and that schedule I posted works. If anything I would slow it down the cooling even more after the 3 hr anneal.

[Morganica]

What a bummer--gorgeous piece. Since this is a fuse and not a slump, and the edges are still sharp, I agree that it probably happened on the way down, and it was most likely because you were going too cool, too fast for this setup.

I tend to view annealing schedules in terms of stress-inducing factors, and your piece has at least two. When I'm trying something new I'll double the schedule for every new factor, so if the piece maxes out at 8mm, and I have two factors, I follow an anneal schedule intended for 24mm (8x(2+1)). If the initial piece comes out intact and I want to make more in that series, I experiment with shortening the schedule in until I find a good compromise that gives me little/no stress in the shortest possible firing time. So...

Factor 1: You're using remelts (pattern bars in this case) which contain a lot of hot colors--reds, yellows, oranges. If I'm going to have problems with a remelt, it will usually be right in the hot color areas, so now I routinely count that as one factor.

Factor 2: You've got black next to white in two different places. In most glasses, whites tend to be much stiffer than blacks with the same level of heatwork, so they won't move as much during the cooldown/contraction period as black glasses. It's really easy to introduce stress between these colors during cooldown, so pairing those colors automatically rates a slowdown.

So..kilns, work and studio environment are different--the schedule that works in one kiln might not work in another. But I'd set up an anneal for 24mm with this piece (and anneal is the ENTIRE cooldown, not just the soak). Like Carol, I also don't get the segment at 480F--most of my upramp thermal shocks take place between 500-700F, so tiptoeing through to 480 wouldn't do me much good. If you're getting a lot of breaks before 480, you might want to check your previous anneals.

Instead, I'd stay slow at least through 700 and spend my time with the bubble squeeze instead of adding dual holds at 1150 and 1240. You've got thin clear glass on top of thick glass, so you need more time to let it come down. That would make my upramp more like this:

150dph to 1240, hold 60
AFAP to 1450 (or whatever process temp works), hold for processing--since you're going faster, without the holds, you probably need more time here

The anneal would look more like this:
AFAP to 950, hold 4 hours
25 dph to 800, no hold
50 dph to 700, no hold
100 dph to 500, no hold
150dph to room temp

That's extremely conservative, and you'll probably find that the right schedule is somewhere between what you're doing now and this, but I'd try at least one at that level to make sure there aren't other things (such as potential incompatibility around the hot glasses, also a possibility) going on.

[Lynn Holman]

Thanks, Cynthia, for your detailed response and explanation. Yes, I probably could lose the slower ramp to 480. I just had the break happen once on a refire, which was most likely due to the annealing on the first fire. I have it in there more as "insurance" but can see the benefit having a consistent ramp all the way up. I was wondering about the black and white too. I've have fired a similar (although smaller - 12" but same thickness) without any issue but there are less hot colors in that piece as well as less b/w area overall. I knew my annealing was not enough and was looking for rationale as to what could make it better. I certainly understand being conservative and then pulling back. One problem I have is that once I have a working schedule, I don't always pull back and thus, why the first ramp is still in my current schedule but I could certainly see that it would make sense with yours.

[Brock]

"Factor 1: You're using remelts (pattern bars in this case) which contain a lot of hot colors--reds, yellows, oranges. If I'm going to have problems with a remelt, it will usually be right in the hot color areas, so now I routinely count that as one factor."

The problem with the ROY colors is a heat induced incompatability.
Lengthening the anneal time just has no effect on incompatability.

[Morganica]

"Factor 1: You're using remelts (pattern bars in this case) which contain a lot of hot colors--reds, yellows, oranges. If I'm going to have problems with a remelt, it will usually be right in the hot color areas, so now I routinely count that as one factor."

The problem with the ROY colors is a heat induced incompatability.
Lengthening the anneal time just has no effect on incompatability.

I'd agree that if the problem is incompatibility, you can anneal hot colors until the cows come home and it won't make any difference. I'm just not convinced that the only thing that can go [edit:wrong] with a hot-colored remelt is incompatibility; I think there must be some kind of viscosity issue there, cool vs. hot, as well.

In one case I made two big bowls with the same hot-/cool-colored pattern bar, two different kilnloads. In the first, I did a standard anneal for that thickness (3/8 inch). In the second, I had another, thicker piece in the kiln and more than doubled the schedule. The fast anneal cracked in the kiln. The slow anneal is still at my sister's house after 8 years, used as a fruit bowl and regularly thrown into the dishwasher. As far as I can tell, the anneal rate was the only difference in the two. Maybe the incompatibility is so mild that other factors come into play, dunno.

[JestersBaubles]

. . . 1 hr 30 isn't long enough for annealing that size of a piece.

Size? You anneal for thickness, not size.

You're being a little too literal .

And while I am not as "seasoned' as most on this board, I believe you anneal for "size" (or dimension if you'd rather) as well. Otherwise, you would have to anneal a 3x3" 2-layer piece the same amount of time you anneal a 30x30" 2-layer piece, which is obviously not the case.

Dana W.

[Morganica]

And while I am not as "seasoned' as most on this board, I believe you anneal for "size" (or dimension if you'd rather) as well. Otherwise, you would have to anneal a 3x3" 2-layer piece the same amount of time you anneal a 30x30" 2-layer piece, which is obviously not the case.

Dana W.

Why not? If the piece is perfectly even, flat and symmetrical, that's exactly what I do. I anneal for the thickest part of the shortest dimension.

Something with a much bigger diameter is more likely to have volume/symmetry/other changes, or be at the kiln's physical limits, either of which might dictate additional annealing. But if it doesn't, I give it the same anneal schedule whether it's 9 square inches or 900.

[JestersBaubles]

Something with a much bigger diameter is more likely to have volume/symmetry/other changes, or be at the kiln's physical limits, either of which might dictate additional annealing. But if it doesn't, I give it the same anneal schedule whether it's 9 square inches or 900.

Interesting.

Dana W.

[Brock]

Not to be too literal, but this is basic. Maybe you should take a course . . .

[JestersBaubles]

Not to be too literal, but this is basic. Maybe you should take a course . . .

I have -- several in fact, and read many books, lots of things on-line... Doesn't mean I think I know everything, I just know what works for me. If I can pass some of that experience along, I'm glad to. If it's incorrect, I'm sure someone will tell me so. If so, great. I'll consider the advice, store it away, and perhaps it will come in useful some day.

Works for me, it's all about learning and sharing, in my view (and being respectful while doing so!). That's my goal here and what I hope I am achieving.

Cheers, Dana

[Clarkie]

It looks like Cynthia covered most of it for you but don't forget the Queen of Pattern Bars, Leslie Rowe Israelson!

[twin vision glass]

Wow Clarkie, you made me blush. How kind. Perhaps my advice would be know your kiln, cold spots in kiln are not friendly to large pieces so adjust where necessary : "When using colour bars" make sure you have annealed the bar well before slicing, (and not over heated it) try to make all of the same thickness for slices or add glass to even out, anneal well for thickness (and for your kiln space and configuration of elements and; are you damming the piece , what is shelf made of, everything you can think of that will trip you up, and use the Bullseye firing schedules as a start point like Cynthia mentioned and tweek for solid colours to multi colours seperated by a line or two or three. So many things to think on for sure when creating the work. Nothing worse than doing all that work and speeding things along or using the wrong schedule when Bullseye has done all the homework for us. (and Uroboros and Spectrum tooo of course.) Les
P.S. you also are using black and white in strip format. Dark absorbs heat and white reflects. Just a thought when designing.