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Heidi K

Member Since 21 May 2013
Offline Last Active Nov 28 2013 11:29 AM
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Posts I've Made

In Topic: COOL ICE - CONE 6 - PORCELAIN CLAY

25 October 2013 - 08:07 AM

 

 

any of you clay  gurus....

 

what, or why is one clay more translucent than others?

 

is it the type of porcelain in the clay body? is epk, grolleg, tile 6, helmer  more translucent than another?

 

if so whats your guess?

 

The short answer is the purity of the kaolin, all the clay bodies discussed in this topic are using a very pure New Zealand kaolin (technically a halloysite), that explains the NZ in NZ6.

 

 

Yeah, I figured the NZ was for New Zealand. I've got a bag of New Zealand Kaolin (supposedly the purest kaolin in the world) and sometimes sub it in a test batch of glaze for EPK and other kaolins. There has to be a lot of kaolin in the recipe to make a difference. I've got to get around to trying NZ6. It may replace my Frost.

 

Jim

 

Jim,

I thought you might be interested to know - I just finally got a batch of frost tumblers out of the kiln yesterday, and without a doubt, the NZ6 is more translucent. I compared the entire batch, but specifically I picked a frost one that was particularly thin and light, and a NZ6 one that was slightly thicker, and still the NZ6 one had more translucence. I was pretty disappointed in the frost tumblers after working for months with the NZ6 (not to mention that my clear glaze crawled on EVERY SINGLE ONE). Looks like I'll be driving to Tacoma for my clay afterall!


In Topic: COOL ICE - CONE 6 - PORCELAIN CLAY

29 July 2013 - 09:18 AM

 

 

Thanks for posting your results Heidi. How is glaze fit with NZ6?    Min

 

I've been having some trouble, but I've found many that fit fine.

I don't mix my own glazes yet, and many of the glazes I use are made at Seattle Pottery Supply. All of the glazes I have from there fit fine except my favorite, shadow green, which doesn't fit at all (the glaze cracks and will either chip off the piece or crack the clay if the clay is thin).

Amaco's PC Ancient Jasper doesn't seem to fit it (though I only tested it on one pair of earrings - the glaze cracked off the earrings), Laguna's Caribbean Crackle crackled to the point that it cracked the bowl I used as a tester, and Coyote's Gun Metal Green sometimes fits it. The first two tests were just at the rim over clear, and it seemed to fit fine (though with a smooth crackle effect), and then the third time it got so crackly that it gave the piece a hairline crack. I forgot that and used it again since, and it worked out beautifully (without the clear underneath it, and it didn't crackle), so more testing is needed with that one.

 

 

Thanks very much for taking the time to write all this! Sounds like you are getting dunting/shivering from several of the glazes you tried. Did Tacaoma Clayart offer any suggestions as to glaze coe? (You might be able to add some high expansion frit to your shadow green and the other dunting glazes to help fit but then you would probably have to tinker with the alumina and silica also.) It's unusual for commercial glazes to dunt, usually they err on the side of caution and use a higher coe. Is there a chance that the glaze layer was thicker than the clay, especially with the Caribbean Crackle or shadow green?

 

Min

 

 

Thanks Min,

 

Yes, I think I'm getting both dunting and shivering. Tacoma Clay Art told me I could try adding a certain frit (I wrote the number down in my studio) to try to increase the coe, but I haven't done it yet. I think I should experiment a little, because shadow green is a wonderfully reliable glaze otherwise and pairs well with so many of my other glazes that I would love to be able to use it on the NZ6, but as of yet I've just been lazy and have busied myself making lots of pure white pieces to showcase the translucence.

The piece that the Caribbean Crackle broke was thin at the bottom where the glaze pooled and got quite thick, so yes, I think it's likely that they were close to the same thickness or the glaze could have even been slightly thicker. The shadow green has never been close to the same thickness as the clay, but always shivers. The time it cracked the clay was on a saucer - the center of the saucer was maybe just under 1/8 of an inch thick (guessing, as it didn't break, only showed multiple crack lines on the unglazed bottom), and where the glaze chipped off I could see it was about 1/32" thick at the most. The glaze was also lifted slightly from the center of the saucer, so it really appeared to me that it wasn't shrinking as much as the clay and was therefore forced to arc as the clay shrunk.  I also tried it (shadow green) on a pair of earrings and the glaze came clear off the clay, like the ancient jasper did. It came off almost in one piece (it stuck slightly around the hole).

 

I can easily avoid the Caribbean Crackle or Ancient Jasper for anything I make with NZ6, but I'd really like to be able to use Shadow Green, so I'll see if I can find it in me to tinker and test.


In Topic: COOL ICE - CONE 6 - PORCELAIN CLAY

29 July 2013 - 08:56 AM

Wow! Thank you, oldlady. That's very nice of you. I'll call them but the shipping will probably negate the savings. If Heidi wants it (Let me know, Heidi), she can have first dibs but I think she is in the Northwest and the shipping for her would really be a killer.

 

Thanks Jim, but yes, I think shipping would be a killer. I'll stick with NZ6 until I see Frost at Seattle Pottery Supply.


In Topic: COOL ICE - CONE 6 - PORCELAIN CLAY

28 July 2013 - 09:39 AM

Thanks for posting your results Heidi. How is glaze fit with NZ6?    Min

 

I've been having some trouble, but I've found many that fit fine.

I don't mix my own glazes yet, and many of the glazes I use are made at Seattle Pottery Supply. All of the glazes I have from there fit fine except my favorite, shadow green, which doesn't fit at all (the glaze cracks and will either chip off the piece or crack the clay if the clay is thin).

Amaco's PC Ancient Jasper doesn't seem to fit it (though I only tested it on one pair of earrings - the glaze cracked off the earrings), Laguna's Caribbean Crackle crackled to the point that it cracked the bowl I used as a tester, and Coyote's Gun Metal Green sometimes fits it. The first two tests were just at the rim over clear, and it seemed to fit fine (though with a smooth crackle effect), and then the third time it got so crackly that it gave the piece a hairline crack. I forgot that and used it again since, and it worked out beautifully (without the clear underneath it, and it didn't crackle), so more testing is needed with that one.


In Topic: COOL ICE - CONE 6 - PORCELAIN CLAY

26 July 2013 - 04:03 PM

 

Well, I'm sad to say that Seattle Pottery Supply doesn't have any Frost at the moment, and Claudia who works there said she wasn't sure if they were temporarily out of it or if they're not going to stock it anymore. I broke down and bought one bag of Cool Ice, but man oh man I hope I don't like it. It's over 5 times as expensive as my usual porcelain!
I was there right before closing and they were really busy. I asked if they had Joe Finch's book of kiln construction, but they didn't know offhand and didn't have time to check. Sorry!


I think you will be disappointed in Cool Ice. It is Southern Ice formulated for cone 6 but it is not as translucent as Frost. Seattle Pottery Supply is one of the best stocked ceramic supply stores in the country. I even have to sometimes order from them even though shipping from WA to GA is a killer because no one else has what I'm looking for. Unless Laguna stops making Frost, I find it hard to believe SPS plans to stop stocking it. The cone 6 porcelain you use (I forget the name) is the only clay I know of that looks like from the pictures you've posted to be as translucent (or maybe even more translucent--which will turn my world upside down!) as Frost.

Jim

 

Jim was correct about my disappointment with Cool Ice. I haven't been back to SPS yet to see if they have Frost back in stock, as I just finally got around to testing the Cool Ice, and got a couple pieces out of the kiln last weekend. Here's a photo of two tumblers, NZ6 on the left and Cool Ice on the right. They're the same thickness, and they're side by side in the same amount of sun, I swear. The difference is stunning.

Attached File  2013_07_20 glow in the light carved tumblers - nz6 with cool ice 3.JPG   179.25KB   4 downloadsAttached File  2013_07_20 glow in the light carved tumblers - nz6 with cool ice 2.JPG   159.81KB   3 downloads