Fixing a break

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Vicki M
Posts: 38
Joined: Sat Aug 30, 2003 10:56 am
Location: Canada

Fixing a break

Post by Vicki M »

:?: Hi everyone,

I have a business acquaintance that wants me to try and fix a broken plate/dish for him that someone else had made. It is a rectangular dish approx 6 inches wide by 12 inches long and 3/4" deep. It has an approx 1 inch lip around the plate before it begins to slump down. I have made a rough drawing with dotted lines showing where the break is on the plate/dish. It looks to be a single clear layer with some frit and stringers fused into it.
He is a denturist so I asked him to make a mold of the plate which he has done perfectly. My question is can I now put a dab of super glue to hold the break together and put the plate into the mold and take it to a tack fuse to mend the break. The break has gone across the corner but also has some of the depth of the slumping to it. Sorry that's the only way I know how to describe it. Can this be done or any other suggestions?
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Morganica
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Re: Fixing a break

Post by Morganica »

Well, I don't think you'd be very happy with the tack-fuse repair. First, even if it it fully fused the line will probably show unless it's disguised with something else.

Second, what's he making the mold of? Refractory plaster? Ceramic slip??? It must be able to withstand the heat of the kiln, and something simple such as plaster of paris isn't stable enough at those temps. It could crack and then the glass would take the impression of the cracks.

Third, a tack fuse will most likely not fully contact the entire surface of the break, so that the joint will be weaker than the surrounding glass. He would have to be careful to never hold the glass by that corner because likely the rest of the dish couldn't take the weight.

Fourth, a tack-fuse mend will very definitely show. In fact, if you added enough heat to make a successful tack, the edges would most likely round slightly, making the break more obvious.

Fifth, if you heated the glass in the mold so that the mend became seamless (at least on top; on the bottom where the glass is cooler it will be much more difficult to blend), it would be moving enough to distort in the mold. If it's only a single layer of glass it will most likely pull in, trying to become 6mm thick, and there's a chance that the two pieces would actually pull away from each other instead of blend. There's also a chance, if you continue to heat, that the glass could wind up in a puddle in the bottom of the mold, although it's less likely with that shape. More likely, you'd get some holes.

If the break is clean, and the edges fit together perfectly, you're probably better off getting a conservation adhesive, such as HXTAL, and gluing it together. HXTAL is nearly optically clear and has a tendency to cover up the breaks it mends so they look seamless. The only question would be whether the break has enough surface area to make a strong joint. If it does, the piece would be repaired with at most a hairline crack. If it doesn't, it would always be very fragile.

The other option is to slump the plate perfectly flat, then figure out some way to disguise the join (with more stringer or something) and fuse the piece again. If it's a single layer it will draw in, so that you'll need to trim off the edges and make it a smaller piece. Then you can slump it into the mold and get closer to the original.
Cynthia Morgan
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Vicki M
Posts: 38
Joined: Sat Aug 30, 2003 10:56 am
Location: Canada

Re: Fixing a break

Post by Vicki M »

Thanks Cynthia,

He gave me the plate today, I just measured it and it is 6mm thick. Looks like it was a piece of clear then frit added and clear capped. I thought there was stringers in it but there isn't. I asked him how it got broken and he said he put it in the dishwasher and when he took it out of the dishwasher it was broken. So do you think it was a stress crack and that maybe there will be more? I think I will just try glueing it back together. I forgot to add, I think he used hydrocal for the mold it is not pure white like plaster of paris, I have it out in the sun drying now as I could still feel a lot of moisture in it. He makes and repairs dentures and makes the molds for them, he has a tiny kiln himself so whatever he uses for his molds for teeth is what he has used for this mold.

Here is the actual plate and mold.
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plate3.jpg
plate2.jpg
plate1.jpg
Morganica
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Re: Fixing a break

Post by Morganica »

Nice piece. I like the gluing idea, too. But if it's a thermal shock fracture caused by poor annealing, which it sounds like, you'll want to dry-fit and make sure the pieces still fit together. Sometimes the shape of the broken piece changes slightly as the stress is alleviated. If they don't fit exactly together, there's less chance of saving it with a runny adhesive like HXTAL--you'll need a gel-like adhesive that fills in cracks, or a way to set up the HXTAL to also act as filler. If they do fit, go for it.

More than likely there won't be another fracture unless you really push it--the stress is now alleviated. But tell the dentist to keep artglass out of the dishwasher unless it specifically says "dishwasher safe."

The mold will work fine in the kiln, but your dentist probably used to much smaller molds (i.e., teeth) that may require a little less drying time. I would let this dry for a couple of days in the sun, but still run it through the kiln at around 240F or so for several hours, until a mirror held up to a kiln vent no longer fogs. Let it cool down completely before using.

You could use the air-dried mold, btw, to help hold the pieces in the right position while the glue sets.

If you're going to try and use the mold to save it, I'd personally first flatten the big piece in a slump fire onto the kilnself. Then I'd put the big piece down on the kilnshelf and set down the broken piece, letting it slightly overlap onto the big piece. I'd suggest putting more frit on top to cover, but unless you know the composition of the glass you might wind up using incompatible frit. You'll have to stick with the glass that's already there.

Now fire slightly hotter than normal. If the resulting blank looks good, trim it to square and slump it in the mold. If you want to try and get rid of any mending seam on the bottom, sandblast it lightly, flip it over and flat-fuse again. Either way, trim the glass to square and slump into the mold.
Cynthia Morgan
Marketeer, Webbist, Glassist
http://www.morganica.com/bloggery
http://www.cynthiamorgan.com

"I wrote, therefore I was." (me)
Vicki M
Posts: 38
Joined: Sat Aug 30, 2003 10:56 am
Location: Canada

Re: Fixing a break

Post by Vicki M »

Thanks again for the advice, I am drying the mold outside for a few days as I put it on some newspaper and I could feel the moisture in the paper. In the meantime I will think about what I want to try, I told my friend there was no guarantee so I might try flattening the piece, I would have to flatten the small piece too wouldn't I as it has part of the slumped shape also. I am thinking it may be bullseye just looking at the red color frit, I have all the 96 colors and this doesn't match what is on the plate. So I won't be able to put any of my clear frit on it. Hmm what to do, what to do. If I do try this would you recommend I use the bullseye firing schedule for slump fuse?
Barb R
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Re: Fixing a break

Post by Barb R »

If you flatten it, the pieces won't fit back together. If you decide not to glue it, I would suggest that you flatten the piece, cut off the part that is broken and then slump it into a smaller piece. Too bad about the break - it's a nice piece.

Barb
Stephen Richard
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Re: Fixing a break

Post by Stephen Richard »

If the pieces fit - glue it. That is the least intervention. Only then try flatening it, as that has a greater intervention, and probably less chance of success.
Steve Richard
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