Advice for a newbie please

[★★Terri★★]

Hi

I have been reading through the posts looking for some guidance and saw that Les said that he used to use an old Cromartie top loader to anneal.

I have the same set up that I use for ceramics and would like to use it for my new addiction - lampwork.

What temp would I need to set the kiln to fire to - I am guessing around 500 C - but an not too sure.  Do the beads just sit on the kiln shelf that has been batt washed (china clay and alumina just like bead release) or should they be suspended on a wire?

Would the cooling down be slower if the beads where muffled in fibre blanket?

Hope you can advise.

Many thanks

Terri

[Redhotsal]

Terri,

I used to use a top loader for annealling. Has to be batch annealing obviously.

You want to ramp up at about 150 - 200 degrees an hour until you get to 520C (Anneal temp for Effetre)

Hold for a minimum of 30 minutes (I use 1.5hours). But this is dependent on bead size. Half an hour is fine for 12mm beads and smaller,

Ramp down at no more than 1 degree per minute (60 degrees/hour)

You must get down to lower than the strain point (which is 449C for Effetre - although call it 400C to be on the safe side).

Then you can increase ramp speed or even turn the kiln off if it's well insulated. If you're turning the kiln off probably best to ramp down to around 300C and then turn off. Don't want to crack the beads through thermal shock.

The crtical part is ramp down from 520 C to 449 C because over this range of temps you still get molecular movement in the beads. After 449 molecular movement ceases and you cannot change the stress in a bead below this temp. If you cool too quick between the strain point and the annealing temp you will actually impart stress into the bead.

I used to suspend my beads on a mandrel off the kiln floor on a pair of kiln props but it doesn't really matter. At 520 most of them aren't going to get sticky but I always felt better that they were off the ground! Certainly batt wash will prevent them from sticking but if the kiln gets accidentally too hot it won't stop them slumping. Incidentally you can use batt wash as bead release but it's not very strong. Great for small spacer beads but not good for anything large and complex.

If you are batch annealling you'll find that you may lose a few beads before you get them to the kiln, however, definitely, use the fibre blanket to aid the cooling of the beads when you make them as that will help to minimise the stress in the beads.

[★★Terri★★]

Hi and thank you for your reply.

I didn't really make myself clear - the controller I have will not control the ramp down. 

I can set the temp I am firing to and set a soak - the ramp is controlled by a rotary dial and I can see the current temp on a digital display and will be able to make fine adjustments if it's too fast or too slow.  I understand from a little I have read that as it's a brick lined kiln the cooling rate will be slow - therefore, firing the kiln down is not really necessay.  Slow cooling is necessary when firing glazed ceramics or they crack and craze like crazy, which is why the kiln is built with a brick lining and not fibre blanket.

Terri

[Redhotsal]

Okay - well, a brick kiln should cool down pretty slowly. But you still need to be careful from 520 down to 400 as that is the critical down ramp, so even if you can't actually ramp you need to make sure the heat isn't escaping too quick. Wrapping the beads in a fibre blanket within the kiln should control the cool rate pretty well unless you want to make really large beads.

You could run a test with some transparent beads and check them with a polariser after annealing to see if it works?

[Teddie]

I am using an Aim 96j to batch anneal my beads. It was my very first attempt to anneal yesterday. I put my beads on a fibre  blanket inside the kiln. I brought the kiln upto 520c it took about 40 mins. I had a quick peep and all my beads had slumped out of shape. On cooling all the beads where left with marks from the fibre blanket. What am I doing wrong? Please help?

[Redhotsal]

I can only say that the temperature inside the kiln was hotter than 520. Sometimes this is the case. My own kiln is hotter than the temp reading says it is. I use "490" on mine even though it is about 30 degrees less than it "should" be.
Your beads should not have slumped at 520 or have had dents from the blanket in them. See if you can get a thermometer or thermocouple in there - you kiln may need calibrating. You could give Lee at Kilncare a ring - he's a very helpful bloke and may have a thermocoupl he can lend you.

[Hamilton Taylor]

For checking kiln temps, B&Q sell a multimeter for electrical testing which comes with a thermocouple, which you can stick in a vent hole in the kiln to verify the annealing temp. When I bought mine, they were about £20, I wouldn't imagine they're much more now...

Sean

[Teddie]

Thanks. I will check it out on their website.

[Teddie]

is that the same sort of multimeter that is on amazon?

[Lee - Kilncare]

Just make sure that the temeperature range will go high enough for you.

Most of these meters will give a temp range in their spec.

[Steampunkglass]

I have a digital multimeter with a thermocouple, although it was a bit deceptive as the meter will go up to 700+ degree c range, but the thermocouple that came with it was only rated up to 280 degrees!

I can use it in my kiln but have had to strip back alot of the insulation, which is the bit that can't handle the temperature so starts to char  I would NOT ADVISE you do likewise unless you really know what you are doing! You can buy proper probe thermocouples that are designed for this if you find the one supplied with it is a cheap low temperature one.