A question for lampwork beads afficionados. In a choice between
using the fabric blanket or the vermiculite, which would you
choose and why? Thanks for replies. Frances
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Frances, about your question regarding fiber blanket vs.
vermiculite: Ceramic fiber acts as a “heat mirror”, but does not
itself absorb heat. What heat it does absorb it loses very
quickly. It’s function as an insulator for hot glass is that it
simply reflects the heat of the hot piece back into itself, so
the piece cools more slowly. But the blanket can’t really be
heated up from an external source and contribute any heat to the
glass (which would allow the glass to cool even more slowly).
Vermiculite is an insulator that is more like traditional clay
materials: it will absorb and retain heat, and give it off
slowly. If you place a piece of hot glass in cold vermiculte, you
will thermal shock the glass because the cold vermiculite will
absorb its heat. But if you place hot glass in hot vermiculite,
the glass will cool very slowly, much more slowly than it will
in fiber blanket.
In the 80’s a lot of glass people discovered fiber blanket for
their annealing kilns as a good alternative to asbestos. But in
the last decade there has been some evidence that the ceramic
fibers also do nasty things to your lungs. There has also been
evidence that the vermiculte may be harmful as well. So
safety-wise, it may be a toss-up.
Personally, I place a can of vermiculite in a large stainless
steel mixing bowl, then surround the can with fiber blanket in
the bowl. I cover the top of the can with a piece of blanket to
keep the heat in, and preheat the whole arrangement on a hot
plate. So I get the best of both: the hot vermiculite insulates
the hot glass, and the blanket never gets hot but acts as a
shield so the vermiculte stays evenly heated throughout the can,
and cools more slowly. The top piece of blanket also keeps the
vermiculte dust down.
I make very large beads and lose none of them to annealing
problems. (I also do run them through a precise annealing cycle
in a kiln after I have a large batch.)
I hope this addresses your question.
Rene Roberts
I used an old crock-pot to keep vermiculite hot while working,
then when finished just shut it off and let the vermiculite cool
down naturally. Cover of the pot keeps dust down and allows one
to use pot for storage between sessions. This eliminates the
necessity for pouring vermiculite from one vessel to another
which raises dust. Martha from Long Island
Rene- I’ve tried something very similar to what you described
(below). I took an old aluminum fry pan, cut a square out of the
side of the top to poke the beads in. In the bottom of the pan I
put clay tiles (for heat) then lined pan with the fiber blanket.
I poke beads in between the layers. It gets up to about 450
degrees, once it heats up. it seems to work better than just the
blanket, but I’d re-anneal big ones in the kiln.
Frances–I have been more successful using vermiculite in a
crockpot. I like this method because I can control the cooling
process. I keep the crockpot set on high while I am making my
beads, then turn the control to Low for a few hours. I turn it
off before I go to bed and the beads are cool in the morning. I
think the slower cooling seems to keep them from cracking. I
had quite a few shatter or crack when using the blanket, which is
how I was taught. Good luck–Vicki
Frances,
I’d go with the vermiculite heated in a crockpot. The blanket
may slow the cooling more than air cooling, but not that much.
Esentially, the blanket is just room temperature. Your beads are
still going to cool too fast. The heated vermiculite will slow
the cooling more than the blanket.
You should also do some “flame annealing”. I do this by
removing the bead from the flame for about 5 seconds, then return
it to the flame for 4 seconds, out for 3, in for 2, and so on.
This allows the inside of the bead to cool a bit while keep in
the outside hotter. It can help reduce stress fractures that
occur when the outside of a bead cools faster than the inside.
Then I put them in the vermiculite in the crockpot. I set the
crockpot on the highest setting and make sure it’s up to maximum
temp before I start.
Of course, nothing beats a kiln for annealing, but I’ve had good
success with the system described above, and it’s certainly less
expensive than an annealing kiln!
Pam East <@Pam_East>
http://www.pinzart.com
Don’t worry about people stealing an idea. If it’s original, you will have
to ram it down thier throats. - Howard Broman
Of course, nothing beats a kiln for annealing, but I've had good success with the system described above, and it's certainly less expensive than an annealing kiln!
I’m coming up 22 years of working with hot glass, and I’d just
like to throw out a word of caution here, about glass as a
material. Unless you are making beads the size of peas, they will
always need to be kiln annealed at some point if you want to be
sure they are completely annealed. There is a precise
time/temperature formula which needs to be adhered to; the bigger
the bead, the longer the time and the more critical the
temperature.
Glass can hold a lot of internal stress without cracking, and
just because it isn’t cracked today or tomorrow, doesn’t mean it
won’t crack next week or next year. Poorly annealed glass can
crack at any time, and often will hold the stress for years and
then break because of a small bump against a hard surface or
change in temperature. If you sell the beads, or put them in
jewelry for sale, you owe it to your customers to anneal them
properly in a kiln at some point.
Rene Roberts
Thanks to all who responded to the question of the fiber blanket
vs. the crockpot with vermiculite. You probably noticed that the
Crockpot is the winner. Now I’m wondering what happens when you
place the bead in the pot and its still on the mandrel, are you
able to put the cover on? I assume you want to retain the heat
as long as possible before and during the cooldown. I also expect
to use the torch annealling method before placing the bead in the
pot and my enamelling kiln after the bead is removed from the
mandrel, for final annealling.
Thanks again.
Visit me or “beam me up” at:
http://members.toast.net/frangro//index.html
On the few beads I’ve done at home I didn’t have another crock
pot to use. However I had an old “Fry Daddy” Electric Frying Pot.
I figured the 450+ degree would be better than 180 degree Crock.
Seemed to work well along with flame annealing, and the
vermiculite is well able to take this low heat. efw
Frances–I place my beads still on the mandrel in the crockpot
with no lid. I just keep the crockpot turned on “high” for as
long as I’m working. I turn it to “low” for a couple of hours
after then finally turn it off when going to bed. It stays hot
for a long time, but cools by morning. This has worked well and
doesn’t seem to stir up much dust. Just plunge the hot bead
deep into the vermiculite!