Gnome Kiln

[shelly]

Hi, does anyone have one of these, if you do could you maybe tell me how to anneal beads, got it given to me for Christmas and have no idea how to use it at the moment, I havnt annealed beads yet as didnt have a kiln.  How do you know when you have done it properly?  Any help would be very welcome.

[babyshoes]

I've just spotted a gnome kiln on ebay - is it this one?

http://www.ebay.co.uk/itm/GNOME-DIGITAL-ELECTRICAL-KILN-850C-1562F-115V-240V-WARRANTY-ACCESSORIES-/221339849863?pt=UK_Crafts_JewelleryMaking_GL&hash=item3388e21487

If so, there is a link to an instruction manual in the listing.

I have been looking at buying a kiln but didn't think this one would be suitable for me to use for annealing beads, as the controller doesn't seem to have the programmable cycles that kilns like the kilncare or paragon ones do. Hopefully someone will come along and prove me wrong - I suspect that you may need to 'babysit' it while it cools or something like that.

[Steampunkglass]

I had one similar to that when I started out, and the controller didn't really give very much fine control, it was either 'on' or 'off,' ok for pmc stuff I guess but not for accurate control with glass. I ended up making my own power controller for it to give a little more fine control, and using a thermocouple pushed in through the gap in the door to try and measure the temperature. I still then had to babysit it and turn it on and off myself to maintain the correct temperatures, then slowly reduce it to cool the beads afterwards. It really wasn't ideal, and moved up to a digitally controlled kiln as soon as I could 

[Moira HFG]

I managed with a manual kiln when I started - but that had a rate setting so you could heat it slowly or quickly. It seems that with this you set a temperature and it goes full tilt until it gets there, so it won't be so easy.

I would do a trial firing with the kiln empty.
Set it to 520 degrees C, and time how long it takes to get there.
Turn it off, and wait to see how long it takes to get down to about 370 degrees.

If it takes somewhere between 30 and 60 minutes to heat up and cool down, you should be OK to try a batch anneal of some small spacer beads in it.

If it doesn't take that long, you could set intermediate times to slow it down perhaps.

For larger, precious beads, I'd wait until I got something with a controller!

Meantime, you could use it for PMC and small flat fusing projects.

Good luck!
Moira

[Moira HFG]

Oh yes, and you can check for proper annealing with polarising film. Search on this site for details!

[Glyn Burton]

Many years ago I had the pleasure of meeting that great potter Michael Cardew, we were talking about his kiln and he said " it doesn't matter how awkward and temperamental your kiln is as long as you get used to the bugger"
Experiment and see what works for you.

[shelly]

Thankyou everyone, have bravely turned it on, it has a T controller so am going to experiment, just anxious as to whether i will know when the beads are done. does the polarising film work on coloured beads as well

[fionaess]

Small world isn't it Glynn - I thought Michael Cardew rang a bell.. He 'started' Winchcombe pottery in Gloucestershire in 1926 and then sold it to Ray Finch in the late '30's.  It is currently run by Ray's son, Mike, who I know well 

[Redhotsal]

Thankyou everyone, have bravely turned it on, it has a T controller so am going to experiment, just anxious as to whether i will know when the beads are done. does the polarising film work on coloured beads as well

It looks as though the kiln isn't programmable - so you'll need to be careful on the ramp down - i.e. you may have to do this by hand. Not impossible but tedious, so I would wait until you have a nice big batch of beads so you don't have to do it very often. That's once you get used to it though. Might be more suitable for PMC users or enamelling to be frank 

Re the polarising - the polarisers show up any stress in the beads. They show up as dark shadows in the glass (which needs to be back lit). It will show you stress on any transparent glass but as you can't see through the coloured opaque sort you won't be able to check for stress. What I used to do is pop in a couple of clear beads and a couple of transparent coloured beads in with your annealing batch and then check them. If they are stress free then there's a decent chance that the others will be too.

The amount of time you need to anneal depends on the size (or more accurately) the thickness of your beads. for "normal" sized beads (up to 15mm diameter) about 40 mins batheing at the anneal temp (520C depending on the glass manuafacturer) should be fine. If you like bigger beads (gobstopper up to 30mm) I would give them 1.5 hours. You need more anneal time according to thickness and this goes up exponentially. e.g. a large paperweight can require 12 hours annealing. At the other extreme they annealed the large glass mirror for the Hubble telescope over a period of many many months. You can't OVER anneal, but you can underanneal, if that makes sense - so always anneal to the largest size beads you have.

[shelly]

Great thanks for that, i had a go yesterday and the all turned into squat things a bit like acorn cups but none shattered  i am using efferte 104 rods at the moment, i put them up to 520 for 60mins so maybe a bit to long, ramped down ok but did it manually allowing 10mins per 50c drop down.  will make some clear beads and have another go.

[Redhotsal]

Hmmm....sounds like your kiln may be hotter than it actually says it is. This is a common thing with many kilns, unless you have it calibrated you won't really know the exact temperature - I don't know mine, but I've gotten used to it. You may want to drop the soak temperature if the glass is starting to slump - try going down maybe 50 degrees(?). You will probably need to get a pair of polarising filters to check your glass. I used to sell them but haven't got any, but you can get them from MUTR - http://www.mindsetsonline.co.uk/Catalogue/ProductDetail/polarising-film?productID=96cfe8a4-6988-47bc-ad34-4192ac866242&catalogueLevelItemID=0484a72e-9923-4237-8295-7a107c7451f4

You'll need a pair - sandwich the bead in between them and hold up to a diffuse light. When you rotate one polariser but keep the other one still you'll see black (or sometimes coloured) shadows in the glass which rotate along with the polariser. In a bead - if you are looking from the top (hole facing you) this pattern is usually a Maltese Cross shape. A properly annealed bead won't show up these shadows - it'll appear clear or dark, uniformly as you rotate the filter. I'll find a link to another thread on polarising which explains in more detail in a mo.

Ramping down sounds ok - but this is actually the most critical bit of the whole process. You'll need to ramp down slowly (ideally at 1C/min) until you go beyond the Strain Point of the glass. This is the point at which the molecules "set" - in other words, if you have stress in the bead at the strain point, then it will remain in there even at lower temperatures. The strain point is around 449C for Effetre - so, the critical drop in temperature is between 520C and approx 440C (though many will say 400C just to be on the safe side). After that you can cool at a quicker rate.

Hope that makes sense? 

[Redhotsal]

We have a Wiki which has lots of good information. Try this link: http://www.frit-happens.co.uk/wiki/Annealing