WHY did they break?

[Havi]

Hi everybody,
I just pulled out of the kiln another glass-boiled piece - and it is broken at the corners. [actually it is the glass from the unsuccessful mesh melt................. I wanted to see what will happen]

The corners are broken, as you can see.

The same happenned with my other attempt to boil glass - it broke, at ther very last mintue when I wanted to move it.
I did the schedule recomoneded - up to 1700, 21/2 hours annealing, ...............

What's wrong? why does this happen??
Can you tell?

Many thanks in advance,
Havi

[rosanna gusler]

looks like you have some kind of unevenivity happening in your kiln. maybe do a series of 'know your kiln' type tests to find cool spots. rosanna

[Bert Weiss]

Why would you spend 21.5 hours annealing a 6mm thick piece of glass??????

What Rosanna said... If there are uneven temperatures inside your kiln, soaking too long will introduce these uneven temperatures in to the glass. If they are greater than 5ºC, annealing will become impossible. A regular short anneal cycle would work just fine.

[Brad Walker]

Why would you spend 21.5 hours annealing a 6mm thick piece of glass??????

I would assume Havi meant 2 1/2 hours, not 21 1/2.

[Havi]

Yes, I meant TWO and HALF hours, not 21.

The unevenness of the kiln might be the culprit. I wonder how would I deal with it. This kiln came back from USA with me at the end of 1987 [!]. I did'nt work with it, though, as I worked as a librarian.
But I suspect there is something there....

If you can advise - I'll be grateful.
If not - I'll check on BE technotes.


Thanks, however,
Havi

[The Hobbyist]

Did they stick to the dam? If so that will cause a break.

Jim

[Morganica]

What Jim said. I don't think this is an uneven kiln problem.

Were you damming the edges of the melt with firebrick? It looks as if the glass stuck to the firebrick at left in the top picture. More likely, the glass hit the firebrick, stuck, and the corners broke off as the glass and brick contracted, probably at different rates. In that scenario, especially if you had glass stuck to firebrick at a 90-degree angle, you'd lose the corner.

I think the second photo goes a fair way to confirming it--you've not only got a corner break (corner crumble, in fact), but you've got a second piece out of the top right side.

[Valerie Adams]

I think Cynthia's right; on the top photo you can even see glass stuck to your dams.

[Havi]

Many thanks for your illuminating remarks.
I accept them, almost completely.

This indicates to me - that it is right what they say that one should kilwash million times EVERYTHING that touches the glass at this temp. of 1700. That, I did not do. I used dams that were previously kilnfwashed.... and not that many layers of shelf primer.

However, at the second piece - the one with the reds - I dammed the left side with shelf primed fiber board. In this case it should not have 'supported' the break in the north corner.... or am I wrong

Additional remark\question , On the first photo, - the blue one - the glass stuck strongly to the fiber sheet [3 m'm] I used underneath it. Is this regular? natural?
Whereas, under the red piece I sprinkled on the fiber sheet some whiting, and it did not stick that strongly....

I am very scared of losing the Dysson shelf - I am afraid that shelf priming wo'nt do its job, thefore I do not risk priming the shelf even million times..... [actually I primed, but them covered it with fiber paper - to be on the safe side]

Thanks for your help,
I always appreciate it

Havi
ps
It is 9 m'm thick. Next experiment I shall put the dams very far, so that it will spread more and become between 3 to 6 m'm thick

[Bert Weiss]

It is tough to figure these things out from photos. Certainly, if the glass stuck to a hard shelf, it will not anneal properly. I am still confused about glass sticking to fiber board. I have never seen this cause such a problem, but I have no experience with 1700º firings.

I routinely coat fiber boards and papers with powdered alumina hydrate. I think this works better than whiting (calcium carbonate), especially as hot as 1700ºF. Whiting is good at 1250ºF, but I wouldn't use it when firing hotter than that. Thinking about this, for papers, you could also use EPK. I don't use the EPK (kaolin clay) on my shelving boards because it doesn't fare well with multiple firings, while alumina is quite durable. But the throw away paper would not have that issue. I think EPK costs less. Kilnwash is a mixture of EPK and alumina hydrate.

Common sense tells me that using 2 sheets of thinner fiber paper is better than a single sheet of thicker. So if the inner sheet tears, the outer sheet is not as likely to also tear. I would dip all the paper in to a bucket of alumina hydrate to lubricate all surfaces. You don't have to leave a lot of powder on the paper, whatever sticks is good.

Without looking up the BE schedules, I am not sure what they look like, but my own schedules for 10mm spend 2.4 hours combining the soak and ramp down 100ºF. So, If I understand it this time, I don't think your schedule is out of line.

[Morganica]

In this case it's pretty obvious--in that first image the glass stuck to the dam matches the breaks.

Havi, I've found that kilnwash isn't always effective as a release when it's facing really hot glass for prolonged periods of time, as with potmelts. I'll slip a piece of eighth inch fiber paper against the dam for much better protection, too. However, it can sometimes ride up the dam a bit when the glass pushes against it, especially if there is a big, thick mass of glass.

In that case, I overlap the fiber paper. I'll either fold the edge of the paper and tuck it under the dam--I may need to add additional weight on the dam to keep it down--or I'll put the fiber paper against the dams first, make sure they are flat to the kilnshelf. Then I'll cut a piece of fiber paper about a quarter inch larger than the space inside the dams and slide it into that space, clipping the corners to make it fit.

The flat fiber locks the dam paper in place.

[Havi]

Interesting.....................

So, how would I treat the [would be] bottom of the piece? Thin fire under the glass, AND underneath it fiber paper 1/8" ???

In any case it will not be the primed shelf but something more reliable than that

I do not think ANYBODY here ever tried to work with such high temp.s as 1700.
But I am happy. I believe that these methods really yield wonderful results, and I have the feeling that once, one learns to controll it a bit - there can be very interesting results - even though it is not completely controllable.
And - as I read somewhere - sometimes the 'bottom' face is even nicer than that which is fascing the lid of the kiln.
[It is not yet clean, but the blue one's 'back' side seems quite nice]

I shall continue experimenting with this.

Many thanks for your help and experience.

Havi

[twin vision glass]

Dear Havi,
I am not sure it is wise to take the glass to such high temps. Perhaps contact Bullseye and ask if something else is actually happening to the glass at that temp and changing some coefficients . Just a thought friend.
Leslie (can you not achieve the same thing at a lower/ longer temp schedule. )

[Havi]

Les,
This is a legitimate question.
I do not have enough experience with this.
Some mesh melt'ers go only as high as 871 Centigrade, which is 1599 F. [which is lower than what I did]

Is there any temprature that you would suggest, Les?

I consider trying it, but have not yet tried. Needs to be checkd / tested.

Perhaps someone who has more experience than mine, who reads this thread will want to share?

Thanks for introducing this ,

Havi

[twin vision glass]

Some of my mesh melts are lower and longer. So I will go up:
- 100 degrees F. per hour to 1220 - Hold 2 hours
- 150 degrees F. to 1480 F. ( if I have dense white in the piece then I will keep it at 1480 for only 15 minutes depending oh the holes) BUT I also have alot of mass and depth to the melts I do so I can re-slice . I really want mine to be about 2 inchs or thicker. AND I have glass in the lower area of the mold tooo so that a really wonderful mix happens. BUT lots of people do not like all the sawing so it is up to the artist.
-I have a suggestion. If you want a mesh melt, spread out the glass over the area and pile the glass high so it really flows nicely together before it begins to go through the mesh. I have a containment mold sitting on the wire mesh as well. BUT it is a Zircar Mold . I will find the link I am talking about as it is abit complicated. Back in a moment!

[twin vision glass]

http://www.bullseyeglass.com/index.php? ... 1348849519
Not sure if this will help out or not. But pile up sections on the kiln shelf and above and you will get some truly marvelous things happening.

[Morganica]

Interesting.....................

So, how would I treat the [would be] bottom of the piece? Thin fire under the glass, AND underneath it fiber paper 1/8" ???

In any case it will not be the primed shelf but something more reliable than that

I do not think ANYBODY here ever tried to work with such high temp.s as 1700.
But I am happy. I believe that these methods really yield wonderful results, and I have the feeling that once, one learns to controll it a bit - there can be very interesting results - even though it is not completely controllable.
And - as I read somewhere - sometimes the 'bottom' face is even nicer than that which is fascing the lid of the kiln.
[It is not yet clean, but the blue one's 'back' side seems quite nice]

I shall continue experimenting with this.

Many thanks for your help and experience.

Havi

I've done "boiled" glass at 1700F or a tad above. It's extremely soft and moving, and the kilnwash is pretty much useless. It can make some beautiful patterns, but I concluded that wear and tear on equipment and me wasn't worth it.

I don't like using thinfire under hot, moving glass. By the time the glass is flowing the thinfire has burned out and softened and can get pushed around. Occasionally it's gotten trapped in the moving glass.

[Havi]

I don't like using thinfire under hot, moving glass. By the time the glass is flowing the thinfire has burned out and softened and can get pushed around. Occasionally it's gotten trapped in the moving glass.[/quote]

So what do you use, Cynthia?
3 m'm fiber paper ?

OR ?

I am thinking of using maybe fiber blanket, as I might want to achieve some 'softening' of the glass effect, but then it would be hard to dam it properly , right?

Thanks,
And thanks for saving my nerves and my equipment - which is not that easy to get here


Havi

[Morganica]

Typically, yes, the thinnest fiber paper I have on hand, which is usually 1/8 inch or 3mm.

[Havi]

Thanks, Cynthia, you made my day.

And a BIG thank you Les, I love the way you make your colorbars, and the way you use them in your pieces.
However it is not my intention.
At this time I prefer doing mesh melts and glass boiling. Perhaps at a later stage I'll have the patience to make color bars the way you make and use them.

Thanks a lot,
Because of you, this board never disapointed me

Havi