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Porcelain Survey


glazenerd

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Good question Ron. I have fired it abusively, just to see how it would tolerate extremes. Fired it from bisq @500F an hour to 2050, then 130F an hour to 2230F. I have made some large tiles and fired them flat with nothing under them: but have not fired it lidded. It has fairly broad mechanical strength, do not think it will be a problem, just have never done it. It is pure porcelain, so bisq to what temp you like: there are no carbons or sulfides present. It will bisq to a very high white.  Try one with and without the lid, not sure what to advise here.

 

Pulled out some test tiles this morning by the way:

 

Fired shrinkage @ Cone 6:  10.5%         CoE: 6.12 est.  Absorption: 0 >> technically I should state it as 0.25%, because my scale is accurate to that range.

 

If you can, glaze one with your favorite glaze and compare it to the same glaze on other clay you have done before. Curious to see what you think of clarity. Potters would be amazed, even how porcelain has colorant effects on glaze.  The higher CoE will make it much more glaze friendly- that was a calculated criteria as well. An area I think the industry needs to change: bring the clay up into the glaze CoE range, instead of forcing potters to blend down their glazes to fit the clay. My 2¢ anyway.

 

Nerd

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Nerd-

Are all three samples in the same photo or are you missing two of them?

Inquiring minds …

Fred

Fred maybe he means just cut that pot in 1/3s??

I think its just one of the 3 and two photos did not load-meaning two are missing .

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Fred:

 

It is National: " Do not post pictures day." I tried to post, said it was too large. Cropped it, tried to post; still too large. So I took my Kodak out to take pictures to post: batteries dead. waves white flag, I give!

 

Nerd

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If you want larger images or just struggling with the post uploader, upload to the gallery and when you are viewing the single image right click, select direct link. Copy the url and attach clicking the image icon on the top bar in your posting. Also that way you get a bigger image shown on the forum without having to click it.

 

Have you done any thermal shock tests? I hear really low absorption is bad for that.

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Joel said: "Have you done any thermal shock tests? I hear really low absorption is bad for that"

 

The normal shrinkage rate for porcelain is 10-11%, it is only when you add ball clays does it rise above this. Fully vitrified porcelain is very dense and compact, and will tolerate normal hot/ cold changes. I have not done all the testing on version 4, but I did on version 3. To date, all I have done is taken a 300F test tile out of the kiln, and drop it into a bucket of cold water. When a body or glaze survives that, then I do the formal testing. Learned sometime back to do some quick tests: and only formally test those that survive.

 

Nerd

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Fred:

 

It is National: " Do not post pictures day." I tried to post, said it was too large. Cropped it, tried to post; still too large. So I took my Kodak out to take pictures to post: batteries dead. waves white flag, I give!

 

Nerd

Grasshopper says

Hey it always happens  all at once-

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Premium porcelains use premium plasticizers: which can have shrink rates off the charts. (15%) Swelling clays ( bentonites) can hold up to 15 times their weight in water: which usually puts porcelain in the 13-14% range. There is a chapter on plasticity coming.

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I'm firing to cone 11 about  1/3 to 1/2 way down-todays fire went to end point cone 11 by mistake.

I have found that one always needs to make their own shrinkage bars as the manufacture numbers are not usually the same as in the users world.

This has been the case for me over many many clay makers and many bodies.

Their are so many variables . For example Laguna tests a bar from every ton but its fast fired in a tiny kiln to cone 10-and cooled quickly . Thats not my schedule or most folks for that matter

Testing is up to the user always-It basically has that disclaimer on every box-user beware clay may shrink or kill you

I always take the shrinkage numbers posted by a clay maker as a loose guide.

 

One last note since I get my clay made in two different water contents that to can affect things as the shrinkage bars are made a tad wetter with the wetter body .I also by all my clay once a year and as time goes by it dries out and becomes firmer-less water.

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I am trying to reproduce sung celadons, and i find that you need .75% to 2% iron to get a good celadon that is iron in the porcelain clay body yes i don't like white porcelains,  and the finer grained it seems the better the glaze looks on it . i make small work  just sugar bowls , bowls of less than 7" and cups  one porcelain i made is really nice but to white it had 50% T-6 kaolin  24% Mahivar feldspar and 32% lake superior brownstone  which is a red brown sandstone from lake superior used in many old building s it is arkosic and has 85 to 90 % silica and 1.5 to 2.25 K20in it with 6 to 8% alumina  it is said that the leftover feldspars in the sandstone are cerisized or partly altered , all i can tell you is i was amazed at how well it threw on the wheel . i fire to cone 8 reduction and the stuff rings like a bell  i don't care for translucency , I am doing some more testing with this sandstone and adding Iron to the mix  i use RED ROUGE which is a polishing compound  sold in the lapidary stores , its 15.00$ a pound but it is so fine its like 5 microns and just is a good colorant for the body .  i tried some red iron oxide 11 years ago and i got speckledglaze and clay body . another porcelain formula is my anoka sand 50% and T-6 50  and this is hard to throw  it want to colaps and soak up water  but you just can't beat the celadon that comes out using this  porcelain as the glaze also uses 56% of the feldspathic sand  the celadon just glows with a soft color like nothing i know  

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 i use RED ROUGE which is a polishing compound  sold in the lapidary stores , its 15.00$ a pound but it is so fine its like 5 microns and just is a good colorant for the body .  i tried some red iron oxide 11 years ago and i got speckledglaze and clay body . 

 

This stuff is approx 0.30 microns, and a fair bit less expensive. 

 

I was working on making a low expansion cream breaking rust a few months ago, I used Alberta Slip in the recipe to supply the iron. Alberta Slip uses synthetic black iron oxide in it's recipe. No speckles in the glaze.

post-747-0-31346000-1498062059_thumb.jpg

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I'm firing to cone 11 about  1/3 to 1/2 way down-todays fire went to end point cone 11 by mistake.

I have found that one always needs to make their own shrinkage bars as the manufacture numbers are not usually the same as in the users world.

This has been the case for me over many many clay makers and many bodies.

Their are so many variables . For example Laguna tests a bar from every ton but its fast fired in a tiny kiln to cone 10-and cooled quickly . Thats not my schedule or most folks for that matter

Testing is up to the user always-It basically has that disclaimer on every box-user beware clay may shrink or kill you

I always take the shrinkage numbers posted by a clay maker as a loose guide.

 

One last note since I get my clay made in two different water contents that to can affect things as the shrinkage bars are made a tad wetter with the wetter body .I also by all my clay once a year and as time goes by it dries out and becomes firmer-less water.

 

I would expect your results to have more shrinkage than the Laguna claim. I've found that my real-world experience with Standard clay bodies have been very close to their published numbers, especially with their stoneware bodies. They put their cone 6 grolleg porcelain #365 at 13.5%, but I always use 15% when calculating for specific sizes and it always works out great. There could be something to thickness and heat penetration going on there, though, as I definitely work a lot thinner than their test bars.

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Once I calculate the plasticity, then I throw it to see how it works.

post-73441-0-28177400-1498229259_thumb.jpg

 

I purposely bend and form sharp angles to see if has the mechanical structure to handle it. Get the formula right, and even throwing novices like myself can make things.

 

Nerd

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I love porcelain. Just use a lot less water or substitute dish liquid for water. Yes it warps, but it is worth the loss of a few pieces. Nothing shows a glaze like good old porcelain. FWTW, porcelain was considered more valuable than gold before potters figured out how to replicate asian wares.

 

 

 

 

 

 

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