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Sputty

Member Since 23 Apr 2016
Offline Last Active Today, 02:20 AM
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Topics I've Started

New Kiln Burners

13 April 2017 - 12:07 PM

My gas kiln is powered by two venturi burners, of uncertain specification and unknown origin. I have a feeling that they are more than a little inefficient, and in any case are sometimes very finicky to use. I also suspect that they are over-powered for the size of kiln I have. It may be that they could be re-jetted, or something, but to be honest I'd rather just get some modern burners.
So, before I buy some new burners, I'd like to be sure I'm getting the correct specification.
The kiln is a traditionally designed down-draft, more or less cubic in shape, with a sprung arch. The overall interior volume is 20 cubic feet.
The burners fire horizontally into minimally bag-walled fireboxes, from diametrically opposite corners.
Gas is bottled propane.
The walls of the kiln are 4-inch thick soft IFBs, with a further 2 inch layer of ceramic fibre on the outside.
Chimney is a little over 12 feet.
The maximum performance required from the kiln is to fire to cone 6 in 8 hours (less would be good). Often, I'm only firing earthenware to cone 03.
According to what I can find, the kiln theoretically requires 200,000 Btu per hour, so 2 x 100,000 Btu burners should be about right.
Any kiln gurus out there who can tell me if I'm about right in my findings? I'd like to get it right!

Many thanks!


Colemanite

19 March 2017 - 03:51 PM

Colemanite in glazes is notorious for causing problems, spitting/blowing off the pot surface. I understand that this is due to rapid decomposition of the material when heated (is that right?).

 

So, is there a case for calcining colemanite to reduce this problem? If so, at what temperature?

 

I'd be happy to use a calcium borate frit instead, but don't have easy access to such a beast in my little European corner.

 

Anyone tried it?


Unearthing Armenia’S Giant, Ancient Earthenware

14 February 2017 - 02:53 PM

I found this Smithsonian article interesting.

 

Unearthing Armenia’s Giant, Ancient Earthenware


Parian Ware Body

25 January 2017 - 05:26 AM

Every so often, I get excited about a new technique. My latest thrill is Parian ware - the cool marble surface is like nothing else (except perhaps cool marble!)

I've searched both this forum and elsewhere for references to Parian ware bodies, and found very little. It's essentially a porcellaneous body, but heavier on the fluxes, which fires to a beautiful marble sheen. No glaze required!

So, I fired a test piece yesterday. The result is very encouraging - the body is vitrified, semi-translucent, a pleasing off-white, and 'rings' nicely - no warping. But the sheen is not quite developed yet - you can just see the beginnings of a bloom. It's nearly there.

The obvious answer is to fire a little higher, or soak a little longer - the test went to a good cone 6. But I am wondering whether I can introduce a small percentage of a frit into the body, to lower the melt a little?

If so, how much to start with? 5%? 10%? And which frit?

The Parian body has a reputation for having a relatively wide firing range as far as porcelain type bodies go - am I sacrificing this by thinking about adding a frit? And what would I be doing to the translucency? Or the castability?

The body is very simple:

China Clay - 40%
Soda Feldspar - 60%

...and deflocculants, to form a casting slip. It's a variation of a Val Cushing recipe.

Or perhaps I could just up the proportion of Feldspar a little?

I have another recipe I have yet to try, from Hamer & Hamer, again for cone 6:

China Clay - 33%
Cornish Stone - 66%

Any thoughts gratefully received!


Mary Wondrausch

27 December 2016 - 08:51 AM

(Site Admins - I don't quite know where to put this post, so please move if it you feel it would be better elsewhere!)

 

Mary Wondrausch, extraordinary slipware potter, died on Christmas Day. She was 93 (I think...).

 

Utterly painterly, truly inspirational, a lovely, lovely person. I think it counts as a good life well spent!

 

A short film:

 

Mary Wondrausch

 

(Plenty more video clips of Mary all over the place.)

 

I have a lovely bowl of hers, in use, as she would have wanted!