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Celia UK

Member Since 01 Jul 2012
Offline Last Active Today, 03:57 AM

Topics I've Started

Urgent Help! Electric Kiln Error / Mistake?

08 November 2015 - 04:21 AM

Had a full glaze load in my Nabertherm electric kiln (my first glaze firing in it). Programmed to 1200oC with a 10 minute soak at the top. However, without me realising it has sat at 861oC for the last 12 hours! I don't know why it has held there, but I suspect I somehow put in a different program number (previous owner used it for onglaze firing and there was a program set for this) and not the one I'd set for my firing. I now have to wait for it to cool to see the damage. Or do in need to let it cool at all?

Any advice on what to do next? Can I just start it again and go to 1200oC or will that total up to too much heat work???

Orton Cones

15 October 2015 - 03:20 PM

So... I've just fired my Nabertherm electric kiln (pre-loved) for the first time, for a bisque firing. I put two cone packs in - one on the bottom shelf, one near the top, with 04, 05, 06 large cones. The program was 100oC per hour to 600oC then 250oC per hour to 1000oC.
I don't regularly use cones, but thought it was a good opportunity to see what the new kiln did and how the bisque firing temperature related to the Orton Cones. I've attached a photo of one of the cones packs - there was very little difference in them.
Does this look as you'd expect? I'm surprised that there's such a big difference between the 06 - completely down and the 05 which is barely bent. I thought the differences between the three would be more even.
Is it telling me that this was a cone 5 1/2 firing or something else?
Don't know why the photo has flipped! I edited one and flipped it myself and that one still imported upside down !Attached File  image.jpg   115.37KB   7 downloads

Cleaning Kiln Shelves

02 August 2015 - 06:20 AM

The kiln wash on my shelves has been flaking off recently, sometimes one layer, in some places 2 layers right back to the shelf. I'd like to remove it all and start over. What's the best way to fo this? Is a sanding/grinding disc the only option? I don't want to end up with gouges in the shelf surface.

Glaze Testing

15 May 2015 - 07:37 AM

Delving into the realms of mixing my own glazes I found a Greg Daly recipe that covered a range of firing temperatures and was the sort of turquoise I love. On a white stoneware test tile (bisqued to 1000oC), glazed to 1074oC it was a lovely bright matt turquoise. I decided to use this for the interior of a set of 7 bowls a friend asked me to make as gifts for old college friends, at a reunion.
I made up a 2 litre batch to the same recipe but with 1% bentonite added. (After reading various posts on CAD!) The specific gravity was 1.64. Not sure of this significance of this and I left it as it was, as it seemed ok for pouring to me.
The only other differences between the test tile and the bowls were that the bowls (v thinly rolled - about 1/10" final thickness, and hump moulded) were bisqued to 1100oC and glazed fired to 1120oC. The outsides had a very dilute manganese wash and I poured the insides for 10 seconds.

This is the recipe
Neph Sy 60; Barium Carb 30; Lithium Carb 5; Kaolin 5
+ Bentonite 1; Copper Carb 4
The test tile and finished bowl photos are attached. Not sure how clearly the colour difference will show. The bowls were much darker, less bright than the test tile and were slightly more towards satin than matt which is very finely crazed (barely perceptible). I do actually think the colour became somewhat brighter as the pieces cooled, if this makes sense to anyone?

So, from my explanation above, can anyone suggest the most likely reason for the difference in the final colour?
Glaze thickness? Firing temperature? Bentonite? Manganese seeping through from outside?

Also, if I want to experiment around this basic recipe, what approach would be worth taking? Which of the ingredients would it be logical to adjust. I have books explaining line blends and triaxials, but some pointers as to how to do that with an existing recipe would be much appreciated.
Now I've fulfilled my friend's brief - (she was delighted) I have time to spend on glaze testing.Attached File  image.jpg   5.1KB   1 downloads[attachment=5326:image.jpg]

Bubbles In Glaze

27 April 2015 - 01:22 PM

I dipped my 'sky' plate (white stoneware - Valentine's ES5), in a Potterycrafts, opaque, leaded, mid-fire glaze (that I see now has a recommended firing range to 1100oC) then sprayed areas using an airbrush, with a dilute mixture of copper carbonate and cobalt carbonate. Fired it to 1200oC (approx cone 5) - oops! With a 10 minute soak. This is the first time I've fired as high as this in my small electric kiln.
The areas with the oxide over are almost ok, but the white areas have tiny bubbles - almost granular in appearance. Photos attached.

So....I've realised the White opaque was fired 100oC above its recommended range, but is that likely to be the problem or is it something else? And why is this only on the areas that weren't sprayed over with the oxide wash? Any ideas?

Attached File  image.jpg   6.3KB   1 downloadsAttached File  image.jpg   5.38KB   1 downloads