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

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  #1  
Old 2015-07-12, 10:50pm
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Unhappy Hollow beads cracking in the kiln.

Hi there
I am just beginning to blow hollow glass beads (about 1 inch diameter) with a small blowpipe using COE104.

Most of the time when they go into the kiln they crack - are they too cool? If so how do avoid this without collapsing the bubble?

Love thoughts, experiences...

Glenda (new to Lampwork, etc.)
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  #2  
Old 2015-07-13, 2:03am
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I don't really know and Larry will correct me if I'm wrong again but I am thinking the heat is leaving the thin areas too fast and staying in the thicker parts near the mandrel longer.

My guess at a fix would be to take 4 times longer evening out the heat distribution at the back of the flame than you think you need in an attempt to get most of it to an even temperature before putting in the kiln.

Good luck.


Got any pictures? Some times the cracking pattern can give clues at to how the stress is distributed.
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  #3  
Old 2015-07-13, 6:51am
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Can you take a long time to wave the bead through the flame intermittently to slowly cool it before putting it in the kiln?
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  #4  
Old 2015-07-13, 7:37am
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Just a few thoughts:
-Are your walls even, or are areas too thin?
-Are you giving the piece a little insurance heat before it goes into the kiln?
-If using tongs to put the piece into the kiln, are you heating the tongs first so they don't shock the glass?
-Is your annealing schedule long enough?
-Is your piece going directly into a kiln?
-Is your blowpipe steel or glass? A steel one acts as a heat sink, so you have to make sure you keep enough heat in it. A glass one requires a lot of monkeying around to get the piece off and cleaned up so the piece will have lost a lot of heat before going into the kiln, again carefully add more heat.
-Some torches work this kind of piece better because they have more radiant heat. If your torch has an outer fire, I'd make that a nice oxy rich bushy flame.
-Boro lends itself to thin walled large hollow beads better than 104 because it is more forgiving heatwise and the finished piece has greater strength. Although, as long as you don't let your walls get too thin in 104, they are doable.
-Are you decorating with 96 frit? With thin walls, it could be incompatibility issues.
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Old 2015-07-13, 11:08pm
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OH, I had not even thought about frit and thinness and incompatibility.

Most frit comes in 93 and 96 coe from what I understand and I don't see 104 frit for sale very often but then again I don't really shop for frit much.
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  #6  
Old 2015-07-14, 2:56am
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Default Cracked beads - replies

Thanks everyone for taking the time to provide me with some possibilities - camera battery flat today so will post photo tomorrow.

I have tried heating before going in kiln using a smaller flame today as my flame is not that wide - they are in the kiln now so fingers crossed.

I am using steel blow pipes and I think sometimes it is that my blow is not even - some thick and some thin areas - not sure yet how to correct that - maybe practice?

Will try what people have suggested and post back.

Again a huge thanks for your generousity in taking time to reply. Much appreciated - as a newbee to forums it is a positive beginning.
Cheers
Glenda (from Australia) where it is freezing at present.
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  #7  
Old 2015-07-14, 5:25am
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If I remember correctly the thing about thickness is one of those "pauses before blowing" ideas.

Seems that if you wait for a four or five count after taking the glass out of the flame, the thicker parts will retain heat and still be kind of plastic and the thinner parts will have cooled enough to stiffen up some and wont be as plastic so they won't get thinner with the pressure of blowing.

But that is one of those "once you have made 100 of them the timing thing seems to fall in place" kind of deals.

So go ahead and make 100 of them, use one color of glass so you can recover the fragments and reuse them with out concern about the mixing of colors.


Oh and different colors are going to have different heat loss and retention characteristics so you probably want to hold off mixing patterns and such until the shaping techniques get comfortable.


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  #8  
Old 2015-07-17, 1:59am
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Default Broken beads - photos

Hi there
Thanks Phil for the wait '5 seconds' suggestion - will be trying that. I have been trying to heat through in a cooler flame before going into the kiln and that seems to be helping.

100 beads is a great suggestion too....

Here's a broken one - you'll see its a very clean crack....

Thanks again for all the tips.
Glenda
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  #9  
Old 2015-07-17, 8:33am
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The position of the break looks like classic thermal / thin versus thick kind of a thing to my limited hollow bead experience.

You may have better luck practicing with transparents. They tend to be stiffer and you can see the thickness some what as you are working.


I do wonder if you are using frit on these and if so you may be adding complexity because most of the commercial frit I get my hands on is 96 coe. If your base hollow bead glass is 104 and then you add frit of 96 your are inducing stress just because of the way the two different types of glass change shape as they cool.

It's a gorgeous bead and you might get away with superglue for a personal use save.
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  #10  
Old 2015-07-17, 5:26pm
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Hi Phill
Thanks - I think the thin, thick diagnosis is probably spot on. My lack of experience in blowing coming to the fore - but working on the 100 blows has begun!

No frit being used but a good point to remember for the future. The superglue idea is one I had - I do like the bead and it is a clean break. I'll work this afternoon with transparents and see how I go.

Again thanks for the tips and kind words about the bead itself.
Cheers
Glenda
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  #11  
Old 2015-07-17, 9:04pm
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Is it breaking where your two sides meet? If so, you may not be giving it a good enough melt before blowing. You may be getting the outside melted, but not the inside which leaves a weakness that can be exploited once blown. After you build both walls and join them, it takes a bit of heat to get everything to melt. Mine seem to shrink a bit at this point because the walls are evening out in the melting process. I like to get a good melt and shape on the base bead before I add more decoration. It can probably be done collectively, but I have the best luck with creating a good base bead first.

IMO, if you are new to hollows, besides making some with transparent, you could make some on a regular mandrel without the blow hole. Learning how the glass behaves when in the hollow form will help you be able to read the glass. Once you can get a good hollow, then add the blow pipe.

White and ivory can be more challenging because they are so soft. I actually love making hollows with white because they flow together so easily, but it does add a layer of challenge compared to using transparent glass.
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Old 2015-07-17, 10:05pm
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Also, I have watched some of the boro folks work with tubing and they had mentioned that letting the shape condense and shrink in a bit and puffing it out and then repeating the cycle a few times can help get the thickness more even overall.

Something again about the way the thin part cools and stiffens and the thick part holds the heat and can expand with the puff pressure and that doing it a few times can spread the thicker parts out and the reheating helps the thin parts thicken up.


Good Luck with this and please post pictures of what you learn. I am seriously hollow challenge myself although I study the details like mad.
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  #13  
Old 2015-07-19, 7:46am
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Thanks again all
I have had much more success - working with various bits of advice - thanks. Only one cracked today - out of a batch of 6 - I think turning the flame down when I work on the holes and flashing the whole bead in and out of the flame lots is working. Also not trying to blow too large, counting to 5 before blowing. Will post some of the results wiht photos.
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  #14  
Old 2015-07-19, 11:15am
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That's Great News Dax!!!
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  #15  
Old 2015-07-19, 6:57pm
daxdesign@bigpond.com daxdesign@bigpond.com is offline
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Default A recent hollow bead - uncracked - yeah!

Thanks again for the support - 4 out of 4 hollow beads uncracked yesterday - yeah...
Glenda
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  #16  
Old 2015-07-19, 7:00pm
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Outstanding Glenda
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  #17  
Old 2015-07-21, 3:38am
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All of these are great suggestions. A few things I remember about blowing hollow forms in 104 glass. As has already been mentioned, cool pot your glass melt it in all the way, keep your gather rotating at all times and thr blow out your hollow part of the way. The first attempt you do not want to inflate it to it's final size, slowly melt it back and condense it down to almost original size. Do this at least two, maybe three times before you blow your final size and shape. Doing this goes a long way in developing even wall thickness. If you are using opaque colors, you may want to make your initial coil pot using moretti black. This glass is just a bit stiffer than some of the other colors. Then encase the black with white or ivory or whatever opaque color you use. This will give you just a tiny bit more control over your gather. Another point I am reiterating is the pause or count to five before ypur final blow. This is very helpful, once you have achieved even wall thickness and you heat your gather in preperation for the final blow, pause for a few seconds. 104 is like soup on a stick so you have time. This will help dissipate (not completely compensate for) any heat differential you may have in your gather. After the pause, blow slowly as you continue to rotate the gather. In time, with practice, you will recognize the amount of glow left in your glass that signals the perfect temperature to blow your hollow form.
Have fun and keep at it.


Otter
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