More Boiled Glass

[jacit]

I have tried the boiled glass technique twice. First: Followed instructions exactly right down to the glass choices...except I didn't have any clear iridized glass. Loved the piece that came out. Perfectly fired; a few tiny open surface bubbles but nothing distracting. However, kiln wash from shelf predictably stuck to the bottom. Only problem.... my kiln won't take the final ramp down from 700 degrees by 600 dph. It shut itself off. Second trial: Got some iridized glass. Repeated the process; changing the 600 dph rate to FULL. Piece developed multiple cracks.... very sharp...so it happened on the way down. Second repeat: Without touching anything in the kiln other than to make sure the dams were tight, I fired it again....stopping the program at 700. Result: some original cracks healed....others developed! I am sure it was because some of the glass stuck to the shelf. Any ideas as to what may have caused this? Kiln wash was fresh.... but thoroughly dry.
I am guessing that I may have gotten the iridized glass in upside down, even though I used the pencil test and had a clear space between the points. Is there any other possibility that you can think of? I really want to use this technique...but now have a very pitted kiln shelf not to mention a ruined piece. Oh.... and I use nothing but BE glass...so compatibility isn't an issue. Ideas?

[marykaynitchie]

Can you go ahead and describe your process using this form? Having all the details organized can help us pinpoint any possible causes:

Project Information:

1) A description of the problem.

2) If possible, a digital image of the piece is and kiln is often helpful.

3) Style codes (i.e. 1101-30), production dates, and sheet numbers for all of the glasses in the project in question.

4) Design of the piece (dimensions, arrangement)

Kiln and firing info:

1) Description of the kiln (type, interior dimensions, controller, etc.). Describe location of elements.

2) Firing cycle for this project (including the annealing portion of the cycle)

Kiln Furniture and supplies

1) What kind of kiln shelf are you using?

2) What are you using for a shelf or mold separator? (Thinfire, fiber paper, shelf primer, etc.)

3) Where is it situated in the kiln during firings?

4) Describe any additional kiln furniture used (dams, molds) and the separators used.

Optional (but encouraged):

Do you have a hunch about what could be done differently to avoid the problem?

Thanks for reading this. We look forward to helping you.

Mary Kay
Bullseye Glass Co.

[jacit]

Project Information:

1) A description of the problem. The irid glass on the bottom of the project stuck to the shelf causing the glass to shatter.... sharp edges.

2) If possible, a digital image of the piece is and kiln is often helpful. Here is a photo of the biggest piece. The rest is is varying sizes.... shattered. The broken edges are VERY sharp.

3) Style codes (i.e. 1101-30), production dates, and sheet numbers for all of the glasses in the project in question. Sorry. I can't do production numbers and sheet numbers. All glass, except the irid, is from scrap sheets that I have had for a while. With the irid, I used most of the sheet and the label is gone..however it must have been a fairly recent run, since I just got it from Ed Hoy. The color/style numbers are: 0011010-0003, 001101-0031, 000120-0030 and 000220-0030.

4) Design of the piece (dimensions, arrangement) 10" square. Bottom layer: transparent Rainbow irid (irid side down), Clear frit Coarse, Marigold yellow, Orange on top. Three full 10" layers. Sides: bordered by Transparent Rainbow Iris (irid side out).

Kiln and firing info:

1) Description of the kiln (type, interior dimensions, controller, etc.). Describe location of elements. Paragon 24 Professional Series.... like the ones you sell in your show room. Elements on side and top. Sentry 2.0 Controller. Interior dimensions.... probably 22" since my 20" shelf just fits.

2) Firing cycle for this project (including the annealing portion of the cycle)
Fired twice: First time:
400F 1100 :30
600F 1700 1:30
AFAP 1500 :10
AFAP 900 2:00
100F 800 :00
180F 700 :00
AFAP 70 :00 (My kiln won't do the 600 degrees your schedule calls for, so I tried this.)

Result..... major shattering. Sharp edges. So I decided to just program the kiln to shut off at 700 and cool naturally and ran the same schedule again. I did not touch the piece in the kiln before restarting it.

Second time.... as above with the modification of shutting the kiln down at 700.

Result....some cracks healed. More appeared. Stuck to glass only on right side....along the edge from center to the front.

Kiln Furniture and supplies

1) What kind of kiln shelf are you using? Cordierite 20 x 20 x 3/4"

2) What are you using for a shelf or mold separator? (Thinfire, fiber paper, shelf primer, etc.)
Shelf primer, Primo Premier. Fiber paper along sides.

3) Where is it situated in the kiln during firings? On 1" kiln posts that rest on the floor. The piece was centered on the shelf.

4) Describe any additional kiln furniture used (dams, molds) and the separators used. I use Bullseye dams along with 1/8" thick fiber paper cut into strips for the edges.

Optional (but encouraged):

Do you have a hunch about what could be done differently to avoid the problem?
I suspect that I accidentally got the irid glass wrong side down.... but then it should have stuck everywhere.... and it didn't. My question to you is............ is there anything else that could have caused this?

[jacit]

Sorry. I have been having trouble getting this loaded. The rest of the piece is in varying sizes of shards. All very sharp edges. So, it definitely broke on the way down.

Boiled glass shattered3.jpg (222.86 KiB) Viewed 5349 times

[marykaynitchie]

Thanks for organizing your info. We don't have experience with Primo Primer here, but I have not heard complaints about it. Can you tell us more about how you applied it? Was it scraped and reapplied before this last firing?

Also, do you have a photo of the kilnshelf after you removed the broken piece?

Was there shelf primer stuck to the bottom of the piece?

Mary Kay

[jacit]

The shelf was scraped before the new primer was applied, however all of the old primer was not removed. The shelf was then vacuumed to be sure that all loose dust was removed before the primer was re-applied. Three coats. This is a new shelf that has only been used once before with primer only, although I always coat new shelves with primer before their first use. That said, I usually use Thin Fire or a combination of fiber paper and Thin Fire. I am sending two photos. The first will be the kiln shelf showing the damage. Those are not ridges of powder... they are craters in the shelf. The second will be the back side of the large section of the glass. Thought you might want to see how the primer stuck to the glass, too.

Boiled glass shelf damage.jpg (137.1 KiB) Viewed 5331 times

Boiled glass backside.jpg (216.92 KiB) Viewed 5331 times

My question is simply, is there anything else you know of that might have caused this other than getting the iridized glass wrong side up? If so, what? I really want to use this technique.

[marykaynitchie]

If you had the irid side down against a shelf that has a sufficient quantity of Bullseye shelf primer (or possibly other kinds of shelf primer) applied, we would not expect you to experience this kind of ruinous sticking.

Mary Kay

[jacit]

That's kind of what I thought. So, I've got it ready to go again...in the morning when I can monitor what's going on. The irid side is DEFINITELY down on the bottom and out toward the fiber paper on the sides. And I made sure that the clear irid strips on the sides are resting on the bottom clear irid glass...not the shelf. The other thing I have done is changed the program so that the last segment decreases at 100 degrees per hour from 700F to 70F. I know it will take a lot longer.... but my Paragon GL24 won't do a decrease of 600 per hour..... and the only other variable I could think of was to control that last decrease in temp. I will let you know what happens when I open the kiln on Thursday. Thanks for your help.

[marykaynitchie]

Good luck! We look forward to learning about your results!

Mary Kay

[jacit]

I am starting to believe in kiln gods! The power went out yesterday thanks to an acrobatic squirrel in the neighbors back yard. My kiln was somewhere below 1500 when it went out and at 758 when it came back on. Since the power was off for about 2 hours, I can guess that the kiln was probably somewhere in the 1000 to 900 range. Anyway, the temp was too low to try to save it by ramping back up. So, I crossed my fingers and shut it off. Needless to say, I have multiple little pieces.
Here is the good news. It did not stick to the shelf anywhere. So, I now know that the fault wasn't in the kiln wash. Hotline's Primo Primer worked just fine. The problem is in the firing schedule.

I know that the last segment of the firing schedule in the lesson on boiled glass won't work in my kiln. It gives me an error message that the rate (600) programmed is too fast for the kiln to manage. So, the change I make is probably in that segment. We also know that a natural cool down is too fast to avoid the breakage. Suggestions??

As a secondary question.... is there any way to remove kiln wash from the back of a whole lot of broken glass so it could be reused?