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Member Since 28 Apr 2013
Offline Last Active Today, 06:27 PM

#86800 Thinning Slip Water Or Deflocculant?

Posted by PeterH on 09 June 2015 - 04:32 AM

This video may be of interest, especially from 3:50

#77279 Can I Swap Neph Sy In This Glaze?

Posted by PeterH on 13 March 2015 - 09:07 AM

I checked packaging and it is just labelled 'Soda Feldspar' as supplied by CTM in exeter

If it's any help to the discussion here is an analysis from CTM's site

http://www.ctmpotter...elspar Spec.pdf

#76564 What Causes Glaze/clay 'tide Mark'?

Posted by PeterH on 02 March 2015 - 06:42 AM

I bought a pot in Cornwall a few decades ago, which appears to have a dolomite glaze over white stoneware body.

Interestingly it seems to have not a tide-mark but significant areas of the browny-orange.

Attached File  _vase_cropped_10cm.jpg   101.28KB   1 downloads


Looked at more closely the areas appear speckled but free from edge-effects.

Attached File  _vase_detail_10cm.jpg   47.94KB   0 downloads


Any ideas what's happening? I go along with the solubles/volatiles theory for the

previously described tide-marks. Perhaps the pot was dipped and finger-wiped,

distributing the solubles uniformly over a significant [unglazed] area?


PS Chris your example seems to show both tide-marks and more solid areas. Would

you like to comment on any differences in treatment?


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#74625 Does Anyone Else...

Posted by PeterH on 01 February 2015 - 09:47 AM

Unfortunately all the hand balms you are talking about are not available here in Switzerland.


FYI these seem to be available via your local ebay.


Working Hands



Bag-balm in a square tin


#74152 Sycamore Pottery Is Selling Red Copper Oxide, Anyone Have Info

Posted by PeterH on 26 January 2015 - 03:18 PM

Red copper oxide is coated with a waxy substance keep it from oxidising in the air. So you will

probably need to add a drop of detergent before it will wet. 

#72164 Trying To Find A Square Plate Mould

Posted by PeterH on 20 December 2014 - 07:43 AM

... and there are always drop moulds


#71688 Adding Subtle Interest To Surface In Electric Kiln To Enhance Visual Qualities

Posted by PeterH on 11 December 2014 - 02:36 PM

I've zero practical experience, but as I understand it you only need to slow the cooling over part firing schedule.


See for example


... and the freebies it offers.


Two examples, each shows a glaze with different firing cycles



#70099 What Type Of Glaze Is This?

Posted by PeterH on 17 November 2014 - 05:07 PM

Marcia, here's another.


Cuerda Seca - esp. applying glaze from about 3:20 and the brush used


#69988 For Christmas.

Posted by PeterH on 16 November 2014 - 04:05 AM

From http://en.wikipedia....ki/Caster_sugar

Caster (or castor[31]) (0.35 mm),[30] a very fine sugar in Britain, so-named because the grains are small enough to fit through a castor, a form of sieve. Commonly used in baking and mixed drinks, it is sold as "superfine" sugar in the United States. Because of its fineness it dissolves more quickly than regular white sugar and is thus especially useful in meringues and cold liquids. Castor sugar can be prepared at home by grinding granulated sugar for a couple of minutes in a food processor.


[31] The Oxford English Dictionary classifies both spellings as correct, but "castor" used to prevail.




#69832 Stuck In The Mold

Posted by PeterH on 13 November 2014 - 09:38 AM

Years ago I saw an article about casting something really difficult, pure alumina I think.

It had practically zero green strength, which made it difficult to extract from the mould.

So they first cast a very thin layer of paper onto the mould, then the slip. I cannot imagine

that this is too good for the mould, and it may reduce mould life by blocking the pores.


If you have a mould you are willing to sacrifice, might be worth a try. From my paperclay

making efforts I would recommend cheap white toilet-paper for making the paper-slip.

It disperses quite readily in water, espicially hot water. [Expensive zeta-potential controlled

paper pulp would presumably be better.] Perhaps you could arange only to cast paper onto

the interior part of your mould.

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#69807 Stuck In The Mold

Posted by PeterH on 12 November 2014 - 06:14 PM

Just to clarify,  I put about an eggcup full of the powder in the toe of an old pair of tights and tied it

off to give a full bag.  I then patted this onto the mould surface. [Actually very similar to the bags

of charcoal traditionally used for pouncing.] I then poured as usual. Actually with my mould I couldn't

avoid pouring straight onto the treated part of the mould.


I found that this definitely helped separation, but wasn't a panacea.


BTW the choice of talc or Neph Sye is to minimise any visible effects on the fired pot. So by all means

test with neph sye, but if you low-fire you may want to switch to talc later.


Actually the first time I emptied an unused tea-bag, filled it with powder, then sellotaped it closed. You just

need something porous enough.

#69789 Store Bought Clay Slip Is Way Too Thick...

Posted by PeterH on 12 November 2014 - 01:41 PM

If you stir ithe slip hard and for some time (e.g. with a paint mixer) does thin down. If so it

sounds like the problem might be excessive thixotropy.


If it remains thick ... duh! Perhaps start by measuring its density.

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#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.
Attached File  quench_350.JPG   47.33KB   6 downloads


Then letting it air cool sitting on a brick

Attached File  air_350.JPG   57.65KB   6 downloads

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.

Attached File  grass_350.JPG   59.03KB   4 downloads

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.