warming the bead and flame anneal???

[bubblefizz]

Was just reading another topic and came across this ...
sorry cant remember which thread it was 

"warming the bead through gently. I would maybe make half a dozen dots, and then I'd give the bead a bit of a bath in the top of the flame. Not enough to melt everything in, but enough to keep the bead from cracking. Then when finished flame anneal very slowly"

whats the difference in warming the bead & flame anneal?
i know keeping it warm to prevent it cracking, but what is flame anneal 
this has confused me for ages LOL

[Shirley]

flame annealing is, as I understand it, about bringing the bead out of the flame very slowly so it cools gradually rather than pulling it out quickly into cooler air. Warming the bead would be done while still working on it.

[bubblefizz]

Thanks Shirleu....so its basicly the same thing? 

[Shirley]

they are opposites - annealing brings temp down, warming brings it back up

[bubblefizz]

now i am confused lol

[Shirley]

When you put dots or other detail on a bead you need to have it either out of the flame or in the edge. Consequently it cools down while you are working. To prevent cracking you would put it back into the flame and gently warm it up and then start working on it again. This would be 'warming ' the bead.

When you have finished doing everything you want to do you then flame anneal it. Warm it so it glows lightly, then very slowly move it out of the flame until the bead cools a bit and the glow disappears. You can then remove it completely, put it in the kiln, vermiculite or a fibre blanket. This is flame annealing.

[Vicki]

& you want to get the bead to the same temp all over rather than having just one area being all glowsome (is that a word)

[Lloki]

I think it may be a new one - but I know what you mean!

[Trudi]

I know when Sal Flame annealed she actually turned up the gas and covered it all in soot!!! I'd never seenor heard of it before!

[Redhotsal]

When you hold your bead up at the top of the flame you are holding it in an area of the flame which is roughly speaking about 500 deg C. This is lower than the melting point of glass and is why you can hold your bead safely up there for as long as you want without any of the features like stringer or bobbles from melting in.

On a dual gas torch like the minor burner, if you turn off the oxygen and have just the propane flame you will find that the temperature of the propane flame alone is also about 500 degrees.

When you finish making a bead its temperature is all over the place. The inside of the bead is likely to be around 800C and the outside could be anything from 800-600 degrees or even less, thus there is a huge temperature differential across the bead. Stress in the bead is caused by the outside being much cooler than the inside. This means the outside of the bead contracts (pulls in) around the hotter core and this is what causes the stress.

If you can hold the bead for a long period in a flame which is around 500 degrees you can allow the inside and the outside to get to the same temperature. This makes the stress a lot less. Usually this means that you put your newly made bead into a hot kiln at about 500 and this will "iron out" the different temperatures. Then you can slowly lower the temperature of the kiln so that the bead is gently allowed to cool - inside and outside at the same rate. Then the bead is fully annealed and ends up being physically stronger than an unannealed bead.

If you don't have a kiln or are aiming to batch anneal then you want to get your very hot and unevenly heated bead down to room temperature as gently as possible. Generally this means putting it into vermiculite or fibre blanket - both of which serve as an insultor to stop the outside of the bead from losing too much heat. But they don't prevent the inside temp from differing from the outside temp so that there is still stress in the bead and it has to be annealled.

If you can even up this heat as much as possible this will help to minimise the stress, so sometimes people hold the bead in a propane flame only (the yellow flame) for as long as they can (usually about a minute). This lets the temperature differential even out somewhat. A black sooty residue will form around the bead which also helps to insulate it (and can be wiped off later). Then, when the bead is put into vermiculite or fibre blanket it is a little better protected than it would have been if you had put it in there straight from the flame. THIS is flame annealing.

Flame annealling does NOT actually anneal a bead but can help with beads which are prone to breaking before they are annealed such as lentil shapes.

To fully anneal a bead you need to get down from 500C to room temp at a rate of no quicker than about 70 degrees an hour. You could in theory flame anneal a bead by holding it in a propane-only flame for about half and hour and then you gradually turn the flame down until it is nothing. This would mimick what happens in the kiln. But, you know what? Life's probably too short......

By the way - you can soak your beads for many hours at the annealing temperature (which is usually around 500-ish C for most types of beadmaking glass) but if you allow the beads to cool too quickly i.e. quicker than 70 degs per hour your beads will NOT be annealed and will be just as stressy as they ever were.

[Ian Pearson]

Great explanation Sal. When I first started working with glass we had no oven and set up a small electric motor to revolve glass in a bunsen burner for maybe 5-10 minutes to relieve stress. My my how times change. Still got your "unannealed" bead in one piece that you made for me at Stratford-upon-Avon.

Ian

[Lush!]

But, you know what? Life's probably too short......

So are my arms!   

This is a brilliant explanation, thanks Sal.  I've seen Di cover beads in soot a few times and have been meaning to ask about it!

[bubblefizz]

Thank you Sal ....very good explanation