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Member Since 28 Apr 2013
Offline Last Active Yesterday, 06:02 PM

#64778 How To Get Started With Old Stains, Etc

Posted by PeterH on 20 August 2014 - 10:30 AM

Basic evening-class stuff, but a test tile with a stripe of each on N glazes one way,

overlain with a stripe of all the colours at right angles shows you the effects of all

N glazes under/over all the others. I wouldn't try with N=40 though!

...  a blank line in one direction [so an Nx(N-1) grid] shows single and double 

coverage of each glaze as well.



#59174 Old Potters Wheel. I'm Fascinated!

Posted by PeterH on 24 May 2014 - 04:30 PM

>Is that the underside of a wheel seen behind him leaning against the wall? It kind of looks like the same circumference so maybe that is what the bottom looks like and might help in figuring all those questions out.


... and could the bottom pivot be standing in-front of the that wheel (like an upside down thumb-tack).


Could be a very nifty way of getting the centre of gravity of the wheel below a single pivot point,

and most of the mass at the circumference.

#56620 Sugar/candy Raku

Posted by PeterH on 14 April 2014 - 03:14 PM

Thanks, but the sugar raku I'm interested in is a variant of the 2-part naked raku process, in
which the refractory 1st coat contains sugar. Normally 2-part naked raku leaves black "crackle"
lines. On the other hand sugar raku -- from the few photos I've seen -- leaves black patches,
often with some sort of halo effect.


Overall effect is something like the left-hand pot in



Every few years I'd try again using the normal 2-part naked raku process, and got a really ugly

pot in a mixture of black and charcoal greys.


Last time I tried cooling it in oxidation, with more interesting results.


Firstly tried quenching as soon as it came out of the kiln.


Then letting it air cool sitting on a brick


Different, but nothing like the pictures I'd seen.


Finally I tried to repeat the second experiment, but botched it. I put it on short damp grass to cool, and

it had fallen on its side by the time I got back.


Obviously it had seen a mixture of oxidation and reduction.


So, I'm interested to know how other people cool their sugar raku.


Regards, Peter


For completeness.

Fired somewhere in the range 1030-1050C.

Slip was china clay 3, flint 2, sugar 2 by volume. I also tried a 3:2:1 mix but it was rather faint.


#55779 Formulating An Exceptionally Refractory Clay Body.

Posted by PeterH on 30 March 2014 - 03:23 PM



I believe that Hessian crucibles were traditionally used for this sort of thing, although I cannot supply a recipe.


IIRC 'Pioneer Pottery' by Michael Cardew has a section on DIY kiln furniture, which might have something helpful

(including advice on multiple firings to develop mullite structures?).


How high a temperature do you want to use. What controlled facilities do you have for crucible preparation.


Regards, Peter







PS Silly me, it's wootz steel isn't it.



... contains the recipe

EPK 40
Calcined Kaolin 20
Tennesee Ball Clay 20
Grog 10
Flint 10

Mix with 500 g water per 1000 g mixture.


For a flavour of authenticity


#55714 Drawing Through A Glaze

Posted by PeterH on 29 March 2014 - 05:18 PM

Another video, showing hoe Phil combines faceting with finger wiping, good potters are a very ingenious lot.


Finally, Phil moves from informative videos into high-pressure telemarketing, but cannot keep a straight face.

#54441 Ceramics Projects As A Means To An End

Posted by PeterH on 11 March 2014 - 07:29 PM



I'm even going to play with using them for making crucible steel or wootz, which has a lovely dendritic structure


Have you tried Damascus steel blades?


I don't know if it's possible with the technology you are using, but I've got a few paper lying around somewhere on

analysis of historic artefacts, and attempts at modern reconstructions if you are interested.


Regards, Peter

#50401 Crazing Problem

Posted by PeterH on 16 January 2014 - 09:36 AM

Essentially the same point as Kevin's. If you have any spare "good" tiles - and they have not crazed on

standing - it might be worthwhile trying one of the freeze-heat torture tests to see if they were on the

borderline of crazing. Indian ink is wonderful in making fine crackle visible.


Regards, Peter

#50015 What To Do With Old, Dry, Moldy Clay?

Posted by PeterH on 12 January 2014 - 02:30 PM


There may be a grain of truth in the suggestion that the Chinese had a special kaolin,

thanks to that wonder ingredient of many old technologies - stale urine.


For those who have access to the scientific journals, its well worth reading:

Weiss, "A Secret of Chinese Porcelain Manufacture"


To make up from the brevity of the abstract, I quote from the 2nd page of:

Rytwo. "Clay Minerals as an Ancient Nanotechnology"



Chinese Porcelain:. Porcelain has been made in China probably since
the 6th or 7th century A. D. Quartz, feldspar, and kaolin were then,
as now, the raw materials employed. The name “kaolin”, for china
clay derived from old deposits on the mountain Kao- ling in China.
Observations had been made since the 9th century about the fact that
“chinese have particularly fine clay which they use to make drinking
vessels with the delicacy of glass; although they are made of clay.”
Such items had great strength, were shaped perfectly by hand, and have
wall thickness of less than 0.4mm! During Mongol domination (1280-1368)
the knowledge was lost.  Ceramics from the following Ming dinasty was
not as thin as before, even they tried to use the most plastic kaolin
deposits they found. Only till the end of the Ming dinasty (1644) thin
ceramics appear again, but in this case those were made from illite,
which has a-priori a considerably higher plasticity than kaolin,
making it easier to handle. The secret of ancient Chinese kaolin-based
porcelain must therefore lie in some technique enabling delicate items
to be formed from kaolin of poor plasticity, which would normally be
expected to require clays of extremely good plasticity. Weiss (1963)
showed that by mixing kaolinite with urea and aging it “The kaolinite
crystals did not dissolve, but the urea-based chemicals penetrated into
the crystal lattice and increased the distance between the kaolinite
layers from 7.2 to 10.7 A.  Rheological behavior of kaolin does indeed
increase strongly with this pretreatment. A kaolin of low thixotropy
subjected to this treatment yields a material surpassing the best ceramic
kaolins and approximating sodium bentonites.


Regards, Peter



#47917 Extruder - Worth The Money?

Posted by PeterH on 15 December 2013 - 05:08 PM

A few hits from the net, quality unknown. Regards, Peter


Make your own gas pipe extruder



Murry Gans’ Do-It-Yourself PVC Extruder




Hand-held clay extruder



Ceramic arts clay extruder entries


... I found the one on woven ceramic baskets a pleasant surprise



#45861 Surform Sanding Tip

Posted by PeterH on 16 November 2013 - 08:05 AM


As a fellow UK resident. Sold among the sandpapers for abrading plasterboard. I used to get it

from B&Q, but they seem to have stopped selling it. Probably still in some big DIY stores and

builders merchants. If not www.ebay.co.uk advertise rolls of the stuff


A major strrength is its resistance to clogging.

Regards, Peter

#45214 Copper Phthalocyanine In Glaze

Posted by PeterH on 06 November 2013 - 07:38 PM

Chris, Thanks for the undeserved complement. Although I was aware that many/most modern artists pigments

are organic I certainly didn't recognise the name (although I've bought Monastral blue artists paint).

However, the wonder of wikipedia gives:


... which gives a formula C32H16N8Cu, and even a picture of the molecule/complex


[In chemists shorthand: the unmarked vertices are carbon atoms, and any attached hydrogen atoms are not indicated.]


Surprisingly the wiki entry suggests that the complex doesn't decompose until about 600C.

Regards, Peter


PS really just a plug for http://en.wikipedia.org/wiki/ as a line of first resort. While I believe it can be a bit iffy for matters

of opinion, it's really rather good for matters of scientific fact.

#45198 Copper Phthalocyanine In Glaze

Posted by PeterH on 06 November 2013 - 03:45 PM

Sorry Vivk, but copper phthalocyanine is largely organic, and will just burn out

in a glaze firing, leaving a little copper behind. Regards, Peter

#42158 New Guy, Strange Question

Posted by PeterH on 06 September 2013 - 04:57 PM


The way this got started, 25-30 years ago a power company lineman found that he could sharpen his pocket knife with a broken ceramic insulator he found along the line.


Sadly the electrical porcelains are also fired to temperatures way beyond "craft" kilns. Try repeating the experiment with

a bit of porcelain, some of these are within the high-fire pottery range.


Regards, Peter


Ever so loosely related. When they started putting telegraph lines across the Australian outback, they kept having to replace

missing [glass?] insulators. They eventually realised that the indigenous people were "mining" them to make "flint" tools. They

they started putting a small pile of spare insulators at the bottom of the telegraph poles, so the in-service insulators were left


#41900 A Good Glaze Book.

Posted by PeterH on 02 September 2013 - 07:24 AM



Start by getting access to a glaze program;both as an aid in making substitutions, and as a first step

in understanding the chemistry behind glaze recipes.  If you don't already have one, you might start

with a free one

... and use online information on materials, starting with 


... the rest of their site is a fund of useful information.


Then look at the late Ian Currie's magnificent book Stoneware Glazes. It's long out of print but you can

read the text at:



Start with Currie part-1, which discusses the interactive effects of fluxes, alumina and silica. Presenting

an informative way of making test tiles to show these effects.


Then read Bailey's book on Cone 6 glazes.

http://tinyurl.com/naogsor (with look-inside)

...  which covers different styles of glaze and gives pictures of the effects of colourants.


Then read part-2 of Currie's book, which covers recreating a very wide range of classical types of glaze. It's

interesting in it's own right, and clearly indicates that Bailey's valuable book largely covers an important but

fairly bland range of glazes. [Not a criticism.]


Finally "Mastering Cone 6 Glazes"


is a sort of master-class in developing a smallish set of "industrial quality" glazes with a little "life" in them.


[More on the net about slower cooling cycles generating richer effects.]


Regards, Peter


A report on exploring fluxes for rutile glazes is given at:



A google image search for Currie test grid glaze will bring up some interesting hits.

#41267 Slips And Engobes?

Posted by PeterH on 22 August 2013 - 06:27 PM

You might start with Robin Hopper's "7 Fun Ways to Decorate with Slips and Engobes"



Regards, Peter