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Earthwood

Pinging/Crazing & Clay/Glaze fit with AMACO PC Glazes

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Hi All,

 

So, I've been futzing around for a while with AMACO PC glazes and several different white stoneware bodies. My problem is pinging and crazing. I almost ALWAYS get pinging after a firing and sometimes will get visible crazing. The aggravating part is that the pinging/crazing is not consistent. For example, I will use a particular clay body, and do (at least I think) everything exactly the same (same clay, same glaze, same application, same firing) but one piece will show crazing and another will be completely fine.

 

Also, I will notice that crazing is sometimes limited to areas where two glazes have mixed together. I most commonly use PC Blue Rutile and Zinc Free Clear when this happens.

 

Clays I use where I have noticed this problem with (INCONSISTENTLY) are:

Standard 240 (rated Cone 6)

School White from Sheffield (Rated 6-10)

20231 also from Sheffield (Rated 6-10)

 

I am looking for consistent results so I guess it might be time for me to find a new clay body (because I am sold on the AMACO PC glazes) on the idea that it is a clay/glaze fit issue.

I have considered getting an AMACO clay.

 

Can anyone share what clay they used SUCCESSFULLY with AMACO PC glazes without crazing? (including no issues with mixing the glazes)

 

Also, any general thoughts about what's been going on in my case?

 

Thanks!!!

 

~ Sam

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I use the Amaco PC glazes quite a bit and have not had any issues with them using Highwater Red Rock and Red Stone cone six clay. Have had problems with Little Loafers and pinging. I see that Standard 240 is a very smooth white clay with very little or no grog, as is Little Loafers. Could that have something to do with it? I've only been firing my own work for about a year so this is just a guess.

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There are one of two things going on. One is that the clay is too refractory for the glaze. This means that it is not melting/ shrinking as much as the glaze. Looks like you are using a white clay bodiy. Red terracotta clays have a better fit as they have more iron in them which lowers the melting temperature. Looking at your work, it looks like you are using white clay.

You could try a red CLAY body and add white slip on top, but this would increase your production time.

The second solution is to slow down the cooling rate of your work, as glazes ping when they are cooling and shrinking. Leave your kiln to cool until the next day when you can remove the work without gloves.

If you were making your own glazes, the solution would be to increase the silica/flint by 3%.

Hope this helps.

TJR.

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You have a mismatch between glazes and clay bodies. The Amaco PC glazes are formulated to fire ^5-6; from firing studio kilns where other potters use the PC glazes, they tend to look best at ^5. Your Sheffield clays are ^6-10, meaning they do not fire to maturity at ^6 and are not fitting properly. Not sure why the Standard 240 clay, a ^6, would fire inconsistently. The two Highwater clays are both mature at ^6.

 

I'd suggest using the PC glazes only on a ^6 clay body, not those for ^6-10.

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It's probably absolutely no help as I'm on the left coast, but I use Venus white from Clay Planet (my vendor in Santa Clara CA).

It has only pinged when I did a layer. Mostly I get great results. Love the breaks on the Albany slip brown!

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I have used them a lot and have consistently had no problem with them even while having lots of problems with other glazes. I have used them on B-Mix, Little Loafer's, Frost, HW Brown Stone, Red Stone, and Riverside Grit. I usually layer them with PC or other types of glazes. My glazes seem happiest when fired using the schedule in Mastering Cone 6 Glazes.

 

I vote with finding a cone 5/6 clay and trying that. And whatever you do, don't open the kiln even to peek before it cools off.

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The only PC glaze i had a problem with was Seaweed, it actually cracked the 3 bowls i tried it on. I used it on standard 259. Some of the translucent amaco glazes tend to craze such as dark green, i've been slowly transferring over to coyote celedon series for craze free translucents.

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