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Tips, Techniques, and Questions -- Technical questions or tips

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  #1  
Old 2011-03-09, 8:30am
julieb julieb is offline
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Default Glass KNOBS - zoozii knob question

I have a questions about glass knobs. I made a set of them for the kitchen and they looked great. I covered the core in white then made the rest of the knob in clear with frit etc. Only one cracked near the beginning and after annealing longer no issues..... However I have tried to make a couple in clear glass.. Some the shape of the press and some in other shapes.... after it begins to cool you can see all kinds of cracks branching out from the core all over.... none of these actually reach the surface and they do look sort of neat but i have tried it in boro and in soft clear and the same thing happens.... I believe its due to the core cooling much faster then the glass so have tried putting the whole knob and mandrel in the kiln to help keep the temp more stable - didn't work...

It makes me wonder what is going on in all of those other knobs were I can't see it due to the opaque glass.... None have cracks to the surface so maybe it' O.K.s... Just wonder how durable its going to be long term. I have had some requests to make clear knobs but am reluctant to sell them until I am sure they are not all going to crack to the surface down the road. I have tried putting my latest knob in the freezer, under hot water, dropping it etc and the cracks / fractures have sort of stabilized and are staying a few mils below the surface....

Any info on what peoples experiences have been on this would be greatly appreciated. I have attached a photo of what the latest clear one looks like...

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  #2  
Old 2011-03-09, 9:36am
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jaci jaci is offline
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You could try putting bead release on the mandrel kit piece, and gluing them afterwards. I know it is a hassle, but it may just be the metal/glass not really getting along as well as hoped. Maybe the metal was not hot enough when you applied the first layer of glass, and it caught a bubble, or made a bubble, and it caused stress later? I am not sure.

The fact that it is a screw on piece, and not a solid mass, may make it so it does not hold the heat as well as a solid mandrel would, and maybe you let the middle get a bit too cold? maybe there is a cooling from the mandrel screw cap opening before it hits the kiln? idk, just throwing it out there if you unscrew the piece and put it in the kiln. Not wait till its cool and then unscrew it. (JUST NOTICED THAT YOU ALREADY SAID THIS... OK.. next. )

Just throwing ideas out there. I have made a few, but not with clear glass, so I have not seen a problem like this if there is one.
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  #3  
Old 2011-03-09, 9:39am
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I've never been able to get any knobs made directly on a metal core to not crack... I ended up giving up on that and now I make them like the old-fashioned glass ones with a long bolt that goes all the way through.
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Old 2011-03-09, 10:23am
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I had the same problem with lamp finials - they all cracked. I now coat the insert with bead release, pull it out after annealing and just glue the insert back in. No more cracks. It works well for bottle stoppers as well.

Robert
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  #5  
Old 2011-03-09, 10:31am
julieb julieb is offline
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Thanks for the input.... I think the clear ones after you clean out the core will actually look nicer- frosted core and then you wont see too much glue at the core... Great idea!
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Old 2011-03-09, 3:50pm
JavaGirlBT JavaGirlBT is offline
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Are those inserts from Zooziis? I made all the knobs for my kitchen, laundry room and three bathrooms using the Marj Bates knob kit from Zooziis. I had a problem like yours using a transparent glass, so I switched to an opaque because it's a little more soupier than the transparent. I made these knobs in 2007 and have not had a problem with them.

I think transparents are stiffer in quality and are less forgiving than opaques for this application. Of course, I really have no idea because I can't see through the opaque.

That being said, Marj Bates has made a living selling her knobs for years, so I think they're probably safe.
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Old 2011-03-11, 7:37am
julieb julieb is offline
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Thanks Ellen,
Good call about the opaques.... I have been rough on mine in the kitchen and they all seem good... So maybe I will glue in for transparent bases and leave the opaque ones on the inserts.

I bought my inserts from Nortel Manufacturing as they are here ins Toronto. I think Marj's look totally smooth where these have a groove so I am not sure. I did buy an initial kit... and the zoozii press... I will have to look into it more.

Thanks for posting I appreciate the input!
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Old 2011-03-11, 7:57am
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I thought yours might have a groove in it. I know Rebekah was having cracking issues with the ones with the groove. I think the groove makes a difference and helps lead to cracking. I would try again with the smooth ones from Zooziis.
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Old 2011-03-11, 8:27am
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The groove could easily set up a stress point in the glass. I've used Marge Bates' inserts. No problems with the cabinet knob inserts but the bigger lamp finials all had cracking problems so it may also involve the mass of metal.

Robert
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  #10  
Old 2011-03-11, 9:22am
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I can't help with the stress issue, but I think that the opaque looks nicer anyway. the insert is not the prettiest thing in the world. That shape is really lovely though. Is that a zoozi press? I don't see that shape on their site.
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  #11  
Old 2011-03-13, 6:17am
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I believe the stress issue is due to the difference while cooling between the metal and the glass so the glue solution may be the safest one

Laurie
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