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St Ives Glass Studio
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Author Topic: slumping into a candle holder  (Read 2654 times)
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sandmor1
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« on: May 04, 2014, 08:22:08 AM »

Hello
I have just bought a square dish shaped candle holder. The glass slumped into the dish shape fine but didn't drop down into the round candle holder centre. (I hope you can understand that)    (Bullseye Glass...2 layers...18cm square)

The schedule I used was
150    600   10min
56      620   30min
9999   516   45min
66      400    0
off

I have used this schedule to slump several plates and dishes in my Skutt Hotstart but clearly it isn't right for the candle dish.
Could anyone offer me a better schedule, please.

Thank you

Sandra
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Zeldazog
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« Reply #1 on: May 04, 2014, 12:47:56 PM »

To be honest, finding the right schedule, for fusing and probably even more so for slumping is about getting to know your own kiln.  Every kiln is slightly different, even two of the same model will fire slightly differently.

So, experimenting is the key - nobody can really give you an exact firing schedule to suit your mould, your kiln, and one can learn a lot by trial and error - but I think you probably already know that you need to fire hotter.

Take a look on the Warm Glass site - there's loads of tip sheets under technical support, or Creative Ceramics who make a lot of slumping moulds.  They both have guidelines for slumping which will vary a lot depending on size and shape of the mould,etc - but you find they offer a good point to start exploring from.


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Glassy Lou
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« Reply #2 on: May 04, 2014, 03:17:47 PM »

Dawn's right. There's no "one schedule fits all" so you'll need to do a bit of experimenting.
I can tell you though that I had to go up to about 700 in my sc2 to get my candle plate to slump fully.
Good luck Smiley
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June
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« Reply #3 on: May 04, 2014, 03:43:13 PM »

I recommend you get the book Contemporary Warm Glass by Brad Walker, which is packed with information and I like The Joy Of Fusing, both of which are on offer at Tempsford Glass. The latter has quite a lot of suggested schedules and both explain how the schedules are made up so you can tweak to suit. We've never been on a course so it really is trial and error!  Smiley
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sandmor1
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« Reply #4 on: May 04, 2014, 05:55:54 PM »

Thank you for all that. I do have the Brad Walker book but not the Joy of Fusing...I think I will get that next.

As I'm a real novice at this, I do have problems with fusing schedules, among other things.  (yes, I know you can tell by the questions I keep asking)

But I will get there...eventually...in the end....It is a very interesting and rewarding hobby, though a little on the expensive side. But what the heck..I don't smoke and my alcohol levels are low, though all that might change as might the amount of hair before get my fusing schedules sorted out. Grin

Sandra
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ajda
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« Reply #5 on: May 04, 2014, 06:42:07 PM »

If you've slumped successfully with that schedule already and this one nearly got there, maybe just try same again but raise your top temperature by 10-20 degrees and/or the soak time by 10-20 mins. I do quite a bit with recycled glass and every batch or bottle is different, so I sometimes fire the same piece several times over. Bullseye glass is quite expensive, but you might be surprised at how little your kiln costs on a firing cycle.
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sandmor1
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« Reply #6 on: May 04, 2014, 10:38:45 PM »

how little your kiln costs on a firing cycle........

That is interesting, I have only had my kiln about 7 weeks so the 1st electric bill since getting it has yet to arrive. 

I have been kind of expecting a very much larger bill...maybe I will get a pleasant surprise.

Sandra
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Zeldazog
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« Reply #7 on: May 04, 2014, 11:08:10 PM »

how little your kiln costs on a firing cycle........

That is interesting, I have only had my kiln about 7 weeks so the 1st electric bill since getting it has yet to arrive. 

I have been kind of expecting a very much larger bill...maybe I will get a pleasant surprise.

Sandra

They used to quote that the Hotstart Pro used 50 pence per firing when I bought mine, which was about seven years ago -  I monitored it one firing at it used 4.5 kilowatts - my bigger Hobbyfuser used around 8Kw in a single firing, still under a quid.

They're very well insulated and hold their heat, far better than your average oven.  The plug in ones are only about 1.8Kw - your kettle is usually 3Kw and other heated items can be anywhere in that range.

A kiln is only heating at full power for a very short length of time during the firing cycle.  That slow ramp in segment one?  Listen to your kiln, it will hum when it's powering the elements - during a slow climb, you will hear them clicking on and off on regular basis.  It's only running at something like 20% power during this part of the cycle.  It will only ever be using it's full power if you have a fast rate of climb which probably breaks down to something like half an hour out of that whole cycle.  It barely uses anything during a controlled cool down.

A lot of people have the misconception that big kilns are expensive to run, but firebrick is such an efficient insulator that it really doesn't take all the kilns power to get the temperature you need.   Warm Glass give an approximate firing cost on some of the kilns they sell.

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chas
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« Reply #8 on: May 05, 2014, 05:09:39 PM »






They're very well insulated and hold their heat, far better than your average oven.



I just read that after remarking how hot the room was while firing at the mo...  I was wondering if it's possible to improve the insulation to ours (Naberthem F110) to help keep heat in.
I can't see why not (assuming no fire risk) though its cooling programme may be affected as it would lose heat more slowly.

Does anyone have an opinion on that?

Back to the question: when we've had trouble 'bottoming out', as has been said it's been either top temperature/hold too low/short or the curved rim over which the glass drops is too sharp - a bigger radius helps. If your mould is shop-bought, that should have been taken care of. Our final schedule for a 20mm sharpish drop was up to 835deg held for 35 mins.
Good luck,

Chas
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Zeldazog
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« Reply #9 on: May 05, 2014, 06:02:32 PM »


They're very well insulated and hold their heat, far better than your average oven.

I just read that after remarking how hot the room was while firing at the mo...  I was wondering if it's possible to improve the insulation to ours (Naberthem F110) to help keep heat in.

Obviously they do give off some heat, which you will feel especially in an enclosed room (when I had my Hotstart Pro at home, my kitchen, which is normally quite cold got really rather cosy during the pre-christmas rush) but  Nabertherm build top quality kilns and Warm Glass quote the firing costs of the F110 at around 1 a firing - for the size and power rating of that kiln, that's extremely frugal, so I'd think it was very well insulated already.

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sandmor1
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« Reply #10 on: May 06, 2014, 07:29:12 AM »

Thank you to everyone with your thoughts and advice on both the slumping of the candle holder and also the kiln running costs.

I have finally got around to refiring the candle holder this morning. (I had a busy w/e)

I have upped the top temp from 620 to 660 and the hold from 30mins to 50mins. It will be out at around 8pm.

I found all the comments on the kiln running costs very interesting. I got my kiln from Warm Glass and I know they are very good but when it comes to electrical products I tend to be skeptical about manufacturers/retailers claims on running costs.

 I am probably being unfair now, as I know things have improved in recent years with regard to publicity claims on products.

Sandra

 
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marklaird
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« Reply #11 on: May 06, 2014, 11:15:55 AM »

Hi Sandra,
Just seen this and thought I would add my slumping schedule if it is any help to you.
I've got an SC2 (also from Warm Glass)
Ramp at 200 to 520C, hold 25min
Ramp at 330 to 650C, hold 20min
Ramp AFAP to 516C, hold 50min
Ramp at 60 to 371C, hold 0
Ramp at 100 to 40C

This seems to work for me on a small 8cm trinket dish with a flat base.

Hope it is of some use.

Mark
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Zeldazog
My name's Dawn, I'm an
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« Reply #12 on: May 06, 2014, 03:06:24 PM »

I found all the comments on the kiln running costs very interesting. I got my kiln from Warm Glass and I know they are very good but when it comes to electrical products I tend to be skeptical about manufacturers/retailers claims on running costs.

 I am probably being unfair now, as I know things have improved in recent years with regard to publicity claims on products.

I put my Hotstart Pro through a plug in monitor and it registered around 4.7Kw for a full cycle.  Even at current electricity prices, probably average around 11p per Kw/H that is still less 53p per cycle - if anything Warm Glass are being overcautious as they quote approximately 75p per cycle.

Similarly they quote 90p per firing for the Hobby-fuser.  I haven't put that through a monitor as it has a facility to tell you how much power it used on a cycle - it was definitely under 9Kw for a full fuse firing, so again, their figure of 90p is about right.
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sandmor1
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« Reply #13 on: May 06, 2014, 07:40:45 PM »

Right...second slump was a little better but still not enough.

Can I go even higher than 660 (top) ? Or should I hold for even longer than 50mins ?

Also, this would be the third slumping....would that be OK ?

Sandra
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chas
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« Reply #14 on: May 07, 2014, 10:13:21 AM »

Right...second slump was a little better but still not enough.

Can I go even higher than 660 (top) ? Or should I hold for even longer than 50mins ?

Also, this would be the third slumping....would that be OK ?

Sandra

Well the robust answer to all three questions is 'yes', but not necessarily together. Part of the problem solving process is to identify the stumbling-block, and too many changes at once may not do that. You'll want to repeat the firing - successfully - on other occasions...

With due respect to your initial creation, you may (may) have to regard this one as sacrificial in the cause of experience, so, I'd whack up the temperature first (50 mins hold is quite long already) take a chance and bake it again!

Or, if you'd really like to preserve this one, you could just cut a plain piece of glass and fire that in the mould to the new experimental schedule.

Chas
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