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Imco Mid-Fire Clay Reviews Wanted


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I recently relocated to Northern California and need to choose new clays. IMCO isn't far away and seems to be a major supplier in the area. I did an internet search but didn't come up with much in the way of comments about their clay bodies, either positive or negative. Does anyone here use clays from IMCO?


I fire Cone 6 electric. Mostly slab-built sculptures in sizes from 12"-24" and occasionally I throw dinnerware (but not at anyone in particular).  :D


Anyone have an opinion? Do their midrange clays actually vitrify at cone 6? How do they handle? Any glaze fit issues? Do you especially like or dislike any of them?


Any comments would be welcome. TIA.

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Thanks. Yes, I can certainly do that, but there was a post on this forum a couple of years ago about the IMCO Stoneware bloating - a defect that I gather has been corrected. If there are issues with other clays in their line, I'd just as soon know about them before spending a bunch of time testing. If possible, I prefer to learn from other people's experience!


Color is less important to me than vitrification, strength, reliability, and ease of handling. If someone on the forum says that one or more of these clays doesn't vitrify at cone 6 or that they are prone to cracking or that they slump at cone 6 or there are other issues, I can write them off my list of potential clays.


For example, another series of posts in this forum talks about the difficulty of working with black clays because of their issues with bloating, etc. For that reason, I won't consider Starry or Night despite their attractive color.


Once I've settled on a couple of clay bodies, I'll adjust the glazes to fit them. I don't foresee a time when I would ever care to make my own clay body - just don't have any interest in it, I guess. So any comments on IMCO clays from those who have experience would be most welcome.

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Have you called them yet and talked with Aaron?


I've used many of the IMCO pugged clays over the years, I have no complaints.  Mainly we make our own clay from dry materials (which I get many from IMCO), but many of our students, local schools, local artists, etc buy their clay and seem to like it.  Heck, I was over there one day and saw a pallets of Leslie Ceramics clay bodies, so I guess they're the one who produces some of Toki's pugged clays.


I have not used the Starry Night, I think that's a newer clay body of theirs?  I have a 50lb bag of that ilmenite they put in it, I got it from IMCO to test out as a potential grog substitute/filler material.



My MIL used to teach HS ceramics in Sacramento and she used IMCO clays most of the time vs Laguna or other brand clay from Alpha, since IMCO delivers and Alpha doesn't.  They fired to ^6, with commercial glazes and I didn't really see any issues with vitrification.  From their IMCO stash I've used over the years:  navajo wheel, great white, 50/50 mix, and sculpture 50, IMCO sculpture mix, Elf White, Stoneware #5 and Sculpture 412.

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Thank you - that's very helpful! I will eliminate Great White from my choices.


When I call Aaron, I'll ask if the ilmenite in Starry Night helps with the bloating issues that are said to be common with very dark clays. I note on their website that they say Starry Night is for oxidation firing only so I suspect it does not.


Thanks again for your comments!

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Ilmenite is roughly 50/50 of iron and titanium dioxide. It really does not play into bloating issues. Bloating in stoneware is usually caused by high levels of feldspars. (KNAO).  That amount of iron in reduction however will make the piece very brittle. Secondly, titanium in that amount will act as a colorant in reduction producing a purple (ish) range. If this clay body was fired much over cone 6 in oxidation: it will still present some problems. Iron is a flux once you cross into the cone 6 range, and increases that effect as temps rise.


Lighter colored stoneware bodies are generally less plastic, and tend to be white after firing. The darker the clay body becomes, the more carbons are involved which can also cause bloating; but also tend to be more plastic. Light buff and tan colored clays typically use kaolinitic ball clays to achieve that color. Darker tans, browns and greys have higher carbon ball clays.... A general rule for picking out stoneware clays.



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phoebe i would not eliminate great white without trying out a bag first. i've learnt my lesson from B mix. some people LOVE Bmix. others dislike it. some people have problems with Bmix and others wonder what are you talking about. 


starry night is a particularly newer clay for IMCO. if you want to try out the ilmenite i would say go to alpha and buy Speckled Buff. the speckles are from ilmenite. big pieces. really beautiful with matte glazes. or satin glazes. i think in starry night its ground up so no speckles. i've done ^5 reduction with speckled buff and no - not a good idea. 


also if you can get to alpha fired arts try out their red stone vs. IMCO Navajo Wheel. i love red stone. i love how it throws. i love how it dries. i love how malleable it is even when leather hard so i can still change its form. its my favorite clay body ever. but navajo wheel i find different. not my fav. too sandy and brittle. if i try to trim it when a little too dry instead of partial ribbons i get crumbles. 


your question was about vitrification. what i have learnt from this board is that if you are a professional potter you dont just believe the stats. you test it out. really if its about business i'd really test it just for myself. 


just so you know i met a ^6 production potter yesterday and she uses Bmix without grog and speckled buff. the production potters who i have met who get their clay from IMCO - do ^10 firing and use their 811Buff and red. 


sadly i have not come across a ^6 white body that i like. 

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Thanks for the information! I called Aaron at IMCO and found out the following:


1. They are discontinuing Sculpture 50; for sculpture he recommended Navajo Wheel 35. I asked about Stoneware 1-C and he said the silica in it is 100 mesh and he didn't recommend it for sculpture either even though it looks quite rough in the image on their website.

2. DC 3-5 may slightly slump at cone 6

3. Starry and Starry Night have Manganese Dioxide, which will out-gas during firing and may cause the glaze to pinhole. It should be bisqued to at least cone 04.

4. The Porcelain 6, Navajo Wheel 35 and Stoneware 1C will all work well with MC6G glazes

5. I didn't ask about Great White, so I don't know what he might have said about it


I need an electrician and a few days without rain before I can get a kiln set up and some pieces made, but I'll get back on the forum once I have something to report. Thanks again for all of your help and information!

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