im confused about kilns and annealing beads what happens if i dont anneal them in a kiln :-\
Basic knowledge of all the science myself but...
Heating the glass to make a bead introduces stress into the glass if allowed to cool too quickly it will simply crack and break.
Vermiculite and annealing bubbles slow down the cooling process enough to prevent the instant breakage but the glass still cools quickly.
Annealing in a kiln either batch or anneal as you go holds the beads at a certain tempriture (520 degrees for 104 coe generally) which gives the molicules in the glass time to 'sort themselves out' and become a more solid molecular structure. Then they are cooled by controlled tempriture drops back down to room tempriture so the molecular state is not altered again.
Beads done in bubbles or vermiculite will hold quite well, enough to hold them until they can get to a kiln. But only up to a certain size larger beads don't hold up well to being batch annealed.
Info in the Wiki also: http://www.frit-happens.co.uk/wiki/Annealing :)
??? yikes its all complecated stuff
See I didn't think of linking the wiki...though I was on my phone at the time
If you remember anything about the science they taught at school, put simply, it's about molecules (remember all those plastic balls connected by sticks in 3D grids?).
As matter (in this case glass) is heated, the molecules move around more and more quickly, until the glass is molten. As the glass cools down, they then slow down and settle into place again. Glass has a 'structure', and if the molecules cool down too quickly, they might not be in the correct 'place', and the structure is weak. Annealing is the process of heating the glass up until all the molecules move quickly, then a slow, controlled cooling process ensures that they are all 'in the right place', making the structure of the glass as strong as it can be.
It looks better when I'm explaining and waving my arms around at the same time tbh ;D
And the science bit, using Scarlet and Tina's explanations.......
Quote from: ScarletLeonard on January 11, 2012, 12:49:57 PM
Heating the glass to make a bead introduces stress into the glass if allowed to cool too quickly it will simply crack and break.
Because the bits on the outside or thinner parts of the glass will cool down more quickly as they are exposed to the air and this conducts heat away from the glass. The inner parts of the bead have warm glass surrounding them so cool slower as this is insulating them and the heat is not being conducted away so fast. So you get stress building up within the glass (think earthquake, where the stress builds up within the earth's crust) if the stress gets too great the glass will break (that's when you get an earthquake).
Quote from: ScarletLeonard on January 11, 2012, 12:49:57 PM
Vermiculite and annealing bubbles slow down the cooling process enough to prevent the instant breakage but the glass still cools quickly.
Because they insulate the air round the beads so the heat is not conducted away so quickly, resulting in slower cooling of the thin bits/outside of the bead, so less stress is created between the warmer inner and cooler outer.
Quote from: ScarletLeonard on January 11, 2012, 12:49:57 PM
Annealing in a kiln either batch or anneal as you go holds the beads at a certain tempriture (520 degrees for 104 coe generally) which gives the molicules in the glass time to 'sort themselves out' and become a more solid molecular structure. Then they are cooled by controlled tempriture drops back down to room tempriture so the molecular state is not altered again.
Quote from: lampworklover on January 11, 2012, 08:51:08 PM
As matter (in this case glass) is heated, the molecules move around more and more quickly, until the glass is molten. As the glass cools down, they then slow down and settle into place again. Glass has a 'structure', and if the molecules cool down too quickly, they might not be in the correct 'place', and the structure is weak. Annealing is the process of heating the glass up until all the molecules move quickly, then a slow, controlled cooling process ensures that they are all 'in the right place', making the structure of the glass as strong as it can be.
The 520°C is the stress relief point where the glass is too hard to deform but where the molecules can still move about a bit. As Scarlet and Tina say, it's the controlled cooling that's important. You raise the temperature to above the stress relief point (usually 520° for coe 104 glass, but can change), then hold it there long enough for the whole of the bead to get to that temperature, so the inside and outside of the bead are all the same temperature, molecules have arranged themselves, then you start the cooling process. You cool at a rate that allows the inside of the bead to cool similarly to the outside, that prevents the stresses forming. (Hang on I didn't explain the stresses above. You get the stress because as things get warm they expand, as they cool they contract. We could go back to molecules and energy etc, but won't. If you want proof of this concept fill a cup with just boiled water from the kettle and wait until it cools, it won't quite reach the top. If you're cooling a bead in the air you'll have a large temperature difference between the inside and the outside of the bead, so the inside and outside of the bead want to be slightly different sizes, so crack!)
Quote from: ScarletLeonard on January 11, 2012, 12:49:57 PM
Beads done in bubbles or vermiculite will hold quite well, enough to hold them until they can get to a kiln. But only up to a certain size larger beads don't hold up well to being batch annealed.
And the reason why larger beads don't like batch annealling is that even though they're being cooled slower in the vermiculite and annealling bubbles it's still too fast and so the temperature difference between the inside and outside of the bead is large enough to cause enough stress to crack the bead.
Quote from: lampworklover on January 11, 2012, 08:51:08 PM
(remember all those plastic balls connected by sticks in 3D grids?).
Yep, part of my job. I updated our window display just before Christmas to models of aspirin, paracetamol, ibuprofen, morphine, heroin and cocaine.
Quote from: lampworklover on January 11, 2012, 08:51:08 PM
It looks better when I'm explaining and waving my arms around at the same time tbh ;D
Doesn't everything? ;D ;D
I hope that helps and is not too much of an essay/lecture.
There's a paragraph in wikipedia here. (http://en.wikipedia.org/wiki/Annealing_%28glass%29)
Thanks for the info ladies i get it now ;D ??? ;D
heres another daft question what would happen if i put vermiculite in a heated slow cooker so it warmed up befor i put the beads in then left it on for a while then turned it off would that help things cool better or would it all go bang :-\
i have the cooling bubbles in the tin and have ordered some vermiculite to put metal enameled beads in to cool when there done.
its the same as using it 'cold' but as it takes longer for the bead to cool and as you are putting them some where warmer the glass stress/ thermal shock is less but still there ...so its better but does not anneal the beads ....that can only be done in a kiln
make sure the beads are cool enough not to get vermiculite dimples before you put them in
not used them but result suggest the cooling beads are better than vermiculate for survival .....check if they can be warmed through as i dont know much about them ...someone will come along who dooes though ;)
In a nutshell, the slower you can allow your beads to cool the less stress is created.
Stress is created because the outside skin of the glass cools a lot quicker than the inside. The outer skin contracts too quickly. This makes the outside skin "too tight" for the inside, which retains it's heat.
It's like putting on a jacket that's too small. Sooner or later something will give. ;D ;D ;D
Ideally you don't let the "jacket" cool too quickly. That means putting the bead into a hot kiln when it is still hot and gently cooling so that the inside and the outside cool at the same rate.
If you haven't got a hot kiln waiting you can use vermiculite. This allows the glass to cool a little slower. There is still stress but not so much as if you just let the bead cool in the air. Cooling in vermiculite or annealing bubbles doesn't anneal your beads, It just attempts to cool everything down slow enough for the glass not to crack.
You can "anneal" this bead by gently taking it back up to the point where molecular movement happens. This is usually at 520C for Effetre but does vary a little depending on the glass. There's a temperature below which molecular movement stops and nothing you do makes a difference to the stress. This is the strain point and is around 450C for Effetre. Heating below this temperature has no effect on the stress, hence the reason for going up to 520C.
When you are at the annealing temperature (520C) you should let the glass sit and "sort itself out". For normal beads up to 25mm diameter, this amount of time should be around 40 minutes minimum. For large paperweights this time can be days as opposed to minutes. Some telecope mirrors (like the Hubble mirror) are annealed for weeks and weeks. Glass is such a good insulator of heat that it takes a long time for the temperature to be the same throughout and the bigger the article the longer it takes.
Stringer isn't annealed, as you may have noticed, but because it is so thin there is little temperture difference between the inside of a stringer and the outside.
When you have the molecules "sorted out" you can then bring the temperature back down to normal but you must do this in a way that the inside and the outside cool together at the same rate, or you will reintroduce stress.
You can't "over anneal" but you can "under anneal". If you under anneal then there's not much point annealing to begin with.
For most of us beadmakers this cooling process (or "ramp down" in a kiln) is around 60 degrees C/hour.
Once you get past the strain point (450C) you can speed up the cooling process as it doesn't make any difference. I usually wait until around 250C (to be on the safe side) and just turn the kiln off. I leave the beads in with the door shut though until everything is back to room temperature.
You can anneal as you go by putting a hot bead straight into a hot kiln. In fact you can keep you kiln hot throughout your beading session and then 40 mins after the last bead has gone in the kiln you can start to ramp the kiln down. This is convenient but not everyone can do this. There's not much point in doing this if you have only made a couple of beads.
Many hobbyists will cool their beads in vermiculite/annealing bubbles and then wait until they have enough beads to make turning the kiln on worthwhile. This is "batch annealing". You take the beads up from cold slowly (at about 200C/min) until you get to 520C. Hold the kiln there for about an hour (depending on bead size) and then ramp down at 60C/min.
You can anneal glass that has stress in it many months after it was made as long as it hasn't cracked in he meantime.
Most bead designers will anneal their work as stressy bead can break hours, days or even years after they were made. There is no apparent reason for this but changes in temperature/ pressure can cause a stress fracture. My friend's beads cracked when they were in an airplane hold - the change in pressure caused the beads to crack. They weren't annealed.
You can actually "see" the stress in a bead if it is transparent. This involves looking at the bead with polarising filters. The "stress lines" show up as black shadows. This is due to the change in "refractive index" of the glass. In other words it shows where the molecules have become more bunched up than normal. An annealed bead doesn't show any stress lines at all.
Wow, draw breath Sal ;D ;D ;D ;D ;D
wow didnt realise i needed to be a scientist to make beads thanks for all the info i have lots of books they tell you how to make beads a bit about kilns but not much about the "why" these things need to be done thanks so much for all the help :-*
Quote from: Lee - Kilncare on January 12, 2012, 11:10:04 AM
Wow, draw breath Sal ;D ;D ;D ;D ;D
Heh! ;D ;D ;D
You don't need to be a scientist to make beads. It helps to know why something does what it does but it doesn't matter, in much the same way that you don't have to know how an engine works in order to drive a car. :)