Hello all ;D
My mind has been pondering, and I would like to ask the following question.
Is there any difference in durability between:
a) Beads that have been cooled in a fibre blanket or vermiculite then batch annealed in a kiln LATER
b) Beads that were "garaged" and kiln annealed as the maker went along
In other words - does kiln annealing reverse any invisible stress that's happened to the bead during slow cooling in fibre blanket/vermiculite? Obviously cracks aren't repaired by the kiln, which is why I wondered about less obvious changes to the bead's molecular structure.
Thank you
Helen
I really don't know for sure, but i'd imagine that most beads that are under stress by cooling first and then batch annealing might well break before they get into clean or during cleaning, or visible cracks might show up.
Sal wrote something a while back about using polarising filters to check the effectiveness of the annealing process, so that might be one way to tell.
Good question, certainly got me pondering now. :)
Oh boy, this has really got me thinking.
My understanding of the behaviour of rigid material under stress is that as pressure builds to a critical point no physical "fracture" occurs until a critical stress point is reached, and then tearing of a sort occurs. Glass is a really poor conductor of heat, so the outside cools, shrinks and solidifies while the inside is still molten. In a bead this creates stresses. Then someone adds to the stresses by tapping the bead, and bang, it pops in half and its creator bursts into tears. So I would assume that any stress created by rapid cooling can be reduced or removed through batch annealing and really slow cooling to below the strain point (or whatever it is called), but any "fractures" or cracks will remain unless the whole bead is raised to a molten state before being cooled again.
I think (and I may be wrong here) that glass being weird stuff goes from molten to solid gradually and so when we anneal it we are actually creating a really really thick liquid, in which the molecules can move about, which is how the stresses are removed. Actual cracks are just too much of an ask.
So in answer to the original question there would only be a difference if a "fracture" appeared in the bead to be batch annealed and the likelihood of this being the case increased with bead size.
Now I need to go and have a cup of tea - apologies for sounding like a school book!
This is a question which has been pondered greatly. It used to be thought that batch annealing wasn't as good as garaging, and batch annealers were almost frowned upon. Thankfully attitudes have changed, because actually the physics and chemistry are the important things to remember.
If cooling in a blanket or vermiculite, don't peek! let them cool naturally and slowly. I use a double blanket on top of a single, the only beads that ever broke on me are the ones I admired for too long (which were also my favourite beads, so that makes sense!)
The thing with glass is to bring it down through the annealing range slowly. Hold it at the stress point so that it "settles", then let cool slowly again.
I batch anneal because I make so few beads in a session, and sessions can be days apart. If I could make lots of beads in lots of sessions, I would garage, just to make it less likely to lose a bead to thermal shock before it cools. No other reason ;D
To be honest, it's down to personal circumstances and choice! ;D
HTH!
In a nutshell:
Cooling in vermiculite doesn't actually anneal but tries to minimise the stresses caused by uneven heating. As Betty said - the outside cools quicker than the inside and this does cause stress. This stress is invisible to the naked eye but can be seen under polarised light, so stresses can be made visible, if the bead is transparent.
There is no physical difference between a bead that was cooled in vermiculite and then later batch annealed as compared to a kiln garaged bead if the annealing is done properly. However, batch annealers tend to have a few more casualities before they get to the annealing stage. It is also a bit harder to "get away" with certain encasing or stringer that isn't melted in well.
If you take any piece of stressy glass up to the annealing temperature (which is around 520 C for Effetre) and let it sit at that temperature for a decent length of time you will eradicate the stress in that bead. The length of time is dependent on the bead size - 10mm bead requires about 30 minutes, a large paperweight will require several days, as glass is indeed a good insulator.
At 520 C there is no melting but there is molecular movement and as long as you hold the glass at this temp for a suitable length of time you can relieve the stress completely.
Molecular movement ceases at the Strain Point of the glass - I believe that this is 449 C for Effetre but there are different opinions on this, so as long as you cool down really slowly between 520 and 449 you wont reintroduce stress. A usual ramp down between these temps is 1 degree per minute for "normal" sized beads. However. If you obediently garage for a couple of hours at 520 and then open the kiln door you will reintroduce stress, so the ramp down - or rate of cooling is actually the critical factor to this.
What happens after 449 is really immaterial and you can cool at what ever rate you want as long as the bead doesn't crack through thermal issues. To be safe I usually ramp down at 60 C/hr from 520 to 350 (just to make sure!) and then increase the cool rate after that.
But essentially - if done properly there is no difference between a batch annealed and hot annealed bead if they are both done properly.
Wow, I would just like to thank all of you for your very comprehensive replies to my question. I am now reassured that the batch annealing method is just as good as garaging as I go along - which is just as well because I can't have my kiln next to me when beadmaking due to space issues.
I am actually using the Japanese Annealing Bubbles to cool my beads since I bought some earlier last month, and I have to say that they are very good indeed - haven't had any casualties since switching to them (I was using a fibre blanket before, which was also good).
Helen x
oooooooo. Japanese annealing bubbles sounds so cool. I just use an old crock pot turned on low and full of vermiculite - very "old tech"
dont u love it when Sal comes along..its like waiting for a bus in the rain...i just love ya Sal
xx
I look like a bus in the rain.....? :'( :'( :'( :'(
Hehe - only kidding - how's the 'flu?
haha...and u make me laff...not good..wondering if its cos i havent got proper ventilation and that is making my throat unbeliveabley painful...u ever had that? x
I've just read somewhere that batch annealing really should only be used for boro, not for soft glass - which if true would rule out all those like me working with 104 and Bullseye, using a HH. Is that really the case? Now I'm not only confused, but anxious!
Until I get a bead door for my SC2 kiln, I really need to be able to batch anneal the beads once they're off the mandrels (i.e. having been placed in either vermiculite or fibre blanket first to cool slowly after making), since obviously I can't get the beads into the kiln while they're still on the mandrels (!?!)... and having set myself up with bulk propane I can't afford the bead door a while yet! Oh fiddlesticks...
Does anyone here batch anneal using 104 and a HH? What are the general thoughts about batch annealing 104 as opposed to boro? Any help or info would be hugely appreciated - thank you!
Sally
I used to with no problem at all - obvioulsy not larger beads. But in general, you can batch anneal!
QuoteI used to with no problem at all - obvioulsy not larger beads. But in general, you can batch anneal!
Thank you, Trudi - just what I needed to know!!
I batch anneal and use a HH. I have a bead door on my kiln, but like Helen I have no space for my kiln to be next to me until I get a shedio. So far so good though and I only really have casualties if I've faffed around too long when I made it or peeked too often. I cool my beadies really slowly in my 'special' fibre blanket tin. This is basically a biscuit tin with my fibre blanket inside it (cut into about 3 layers to fit in) and a 'bead door' cut into the side. I then lift up the lid and pop in the bead on it's mandrel. It works brilliantly and really keeps in the heat. I'll see if I can find a pic of my invention. Perhaps I should patent it ::) ;D
Julia x
I definitely ditto what Sal said.
There is no difference between batch annealed beads and garaged beads, the annealing cycle makes them the same.
Also beads are very stressy before they're annealed. If you cleaned one with a diamond reamer it would split, but when annealed it won't.
No you can't repair a crack by annealing as it doesn't get hot enough to flow to mend.
You also can't break a bead by ramping up your kiln to the annealing range quickly. I regularly batch anneal beads by ramping up in about 20 mins and have only ever had 2 beads break, and they already had cracks in them, so I knew they'd split.
Hope this helps :)
QuoteI cool my beadies really slowly in my 'special' fibre blanket tin. This is basically a biscuit tin with my fibre blanket inside it (cut into about 3 layers to fit in) and a 'bead door' cut into the side...
Wow - that's really inventive! I was trying to think up a way to combine fibre blanket with the Vermiculite (or japanese beads) and a crock pot ... Really paranoid right now about getting all this right!
Like you, Jules, it's a question of space - I can't set up my kiln in the "conservatory" that I've now taken over to do my beads in, and my SC2 kiln is in the old utility room the other side of the house - there aren't enough plugs and power points in the conservatory to set it up there, even if there were room, so there's no chance of garaging them while I make them.
I was getting panicky about how long you can keep beads warm in the fibre blanket (or Jules's annealing tin!), before carting them off to the kiln at the end of a session? Is time a factor?
Hi
What you do is leave your beads cooling in the blanket... After about an hour they will be almost totally cold. You don't need to anneal them straight away, as they will be fine until you decide to pop them in the kiln. I batch anneal my beads once every 2 weeks or so, once I have accumulated a nice big pile of them :) Most are absolutely fine this way (there's a few rare exceptions, but don't worry about those for now)
Helen x
QuoteWhat you do is leave your beads cooling in the blanket... After about an hour they will be almost totally cold. You don't need to anneal them straight away, as they will be fine until you decide to pop them in the kiln. I batch anneal my beads once every 2 weeks or so, once I have accumulated a nice big pile of them...
Helen - thank you so much for that - that's just what I would need to be doing, but wasn't sure it was possible. So presumably I can also take the beads off the mandrels before annealing them, which means I can use a kiln without a bead door...?
Sally x
I know someone who works on the ground floor and runs downstairs to the basement with every bead as it's made to garage it. :o
She's fit :P ;D
Many years ago when my workshop was being refurbished I relocated to a porta cabin about 5 mins walk away from workshop. No space for annealing oven so used to carry hot glass outside along road to workshop where oven was. To protect hot glass from weather I put glass in heat resistant blanket and then a large cardboard box. One day the glass was very hot and not completely covered in blanket. Half way up road box which I was carefully carrying in my hands caught fire. Rather than drop the flaming box and break the glass, I just run fast to the workshop/oven. Witness say that as they looked out their windows they could believe their eyes to see a man with seemingly his hands on fire breaking the world record for a 50 metre dash!!!!
Ian
:D :D :D
Just to add that when batch annealing your beads, yep you can just pop them in a pile into the kiln or alternatively you can put them back on your mandrels so they look like kebabs and anneal them that way.
do you put anything under them helen or just pop them on the kiln shelf? i have been using thinfire paper i used to fuse with, but its probably just a bit of a waste?
I just pop them on the kiln shelfy thing ;)
QuoteI just pop them on the kiln shelfy thing
Is that the kiln-furniture type solid (and heavy) ceramic kiln shelfy thing? As opposed to the lightweight fibre board shelfy thing? I have my regular kiln-washed kiln shelf propped on small kiln posts (to allow heat to circulate) - I'm assuming that's okay as the set-up?
Sally
mine just go on a normal wall tile - sat on the bottom of the kiln!