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Black Clay Advice

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Very new to ceramics... I just bought some new black clay (made black from iron ore) and was wondering about glazing... If I dip the greenware in white slip will the iron ore still interfere with the glazes applied later on? Is there any resources where you can see how colours will change with black clay? Thanks!

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I agree- make test tiles. I am a bit annoyed with this clay. My white bead slip works on it but my glazes blistered and bubbled. I want follow this post to see what others have done. I have been using it unglazed.

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(made black from iron ore)

If this is the case; it would take well above 10% to get to black. If that is the case, then it would help to explain this:

 

but my glazes blistered and bubbled

The high iron is not causing it, but it would certainly act as a flux; sealing the body very quickly. This would then mean, off-gassing would take an extended hold to fully resolve. If you are firing to cone 6 ox: then you would need to ramp to 2050F, and then climb @ 125-130F up to 2230F: with short hold. 2050 to 2190 is when all the serious off-gassing occurs, and it is also the critical clay vitrification temps. Ramp up to 2190-2230 to quickly, then you seal the face of the clay and trap gas: which in this case, with this much iron: would compound that problem even further.

 

Nerd

 

Edit: I wonder why they choose to use black iron in a clay body> Surely they know iron is a flux in clay body, when you get into the cone5-6 range, and increases as you go to cone 10?...Sort of an odd choice.

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Very new to ceramics... I just bought some new black clay (made black from iron ore) and was wondering about glazing... If I dip the greenware in white slip will the iron ore still interfere with the glazes applied later on? Is there any resources where you can see how colours will change with black clay? Thanks!

 

 

Ive seen a lot more black clay that's made black by the inclusion of manganese than iron.  Point being, I would double check whats making that clay black.  Manganese has a pretty huge stigma attached to it, due to it being really toxic stuff when improperly handled, so its possible that it's listed in the fine print.   Best to know exactly what you're dealing with before you start chasing down solutions.

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I bought some Flinthills dark brown that fires black and did some testing on it, I only had two glazes that I found acceptable and decided it was too much of a problem to work with.  My clay supplier talked me into trying it.   Denice

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Marcia,

It is PSH 540i (pottery supply house).

 

Mousey: good call, I looked up the msds and it lists ferrous oxide,ferric-ferrous oxide, and titanium dioxide. Again very new so not sure if the first two are synonyms for iron ore (wikipedia tells me yes) but thanks I was just going by what the ceramic store had told me.

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My local supplier is Evans Ceramics, they also have a mold making company that they bought several years ago.  Don the owner told me how popular it was and interesting to work with.  The clay is extremely coarse and rough I can't imagine trying to throw with it or even hand build.  I think he was just trying to get rid of it.    Denice

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(made black from iron ore)

If this is the case; it would take well above 10% to get to black. If that is the case, then it would help to explain this:

 

but my glazes blistered and bubbled

 

 

Edit: I wonder why they choose to use black iron in a clay body> Surely they know iron is a flux in clay body, when you get into the cone5-6 range, and increases as you go to cone 10?...Sort of an odd choice.

 

tom i can't make out if you are being serious or facetious. 

 

you'll be surprised how popular black clay is (our supplier though questions us and warns us before they ring up the clay body). Last spring when i attended the CCACA i saw a lot of Black Mountain amongst ^10ners. underglaze and black mountain rather than glaze. in other words quite a bit of sculpture work. And some functional too with clear over underglaze.  there was a lot of black clay amongst ^6ers too but i didn't enquire what their clay body was except a few who used Cassius Basaltic.

 

thankfully our local clay store always makes sure we understand what clay we are buying and what it would do in reduction. if there are speckles what they are and that we understand how it would affect the final result. how it would feel throwing. made a couple of people in my class not buy it for a few semesters till i started experimenting with it following the store's guidelines and reading the manufacturer's info sheet.

 

dont know if the other manufacturer's store would do the same. if they have the manpower to share that info. 

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I can't see using black clay unless you are going to leave it unglazed or minimally glazed - like with a very thin coat of gherstly borate. We have had trouble with black mountain clay blistering at times. But it does make for beautiful sculpture pieces. Seems like if you get the black clay you would want to let at least some of the beautiful deep rich color show through.  But just my opinion. A lady at our studio does beautiful pieces in black mountain and gets just some highlights or small areas of decoration with underglaze applied to greenware.   GL    rakuku

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yes black clay is a little hard to handle with the blistering. you just need to understand how to deal with it under your circumstances. for instance since i didn't have any control over the firing, i discovered if i used a liner glaze and partial glaze outside i eliminated the blistering. 

 

however i have seen velvet underglaze used on black clay and i can't wait to do that myself one day. the colours were so rich and vibrant. so i can see why people like black clay. as long as they are willing to work with it. 

 

but yes you are absolutely right. why use black clay if you dont let it show through. when i glazed my first piece i immediately noticed my mistake. after that i partially glazed the rest. 

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tom i can't make out if you are being serious or facetious.

Preeta: Serious indeed.

 

Iron in a clay body at cone5/6 and above is considered a flux, not a colorant (it will do both). To get black in a glaze or clay using iron, you have to be well over 10% additions. That much iron will seal the face of the clay rather quickly; trapping gas. Just makes me wonder why they chose iron as a colorant for a clay body; anyone familiar with clay formulation would know about iron being a flux.

 

Nerd

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Black clay is really hard to work with. Just plan on putting in the time. I know I did, and I still ended up abandoning it. I wish I had those 6 months of my clay testing life back. Make sure you test your schedule with one or two pieces before you fire an entire load and have massive bloating issues. 

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I LOVE black clay (I use the Basaltic), and the more/bigger bloats and blisters the better! Unglazed or partial clear...never covered up!  (Well, never say never...I've actually been thinking of a certain rchly colored satin that might look terrific.)

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Thanks for everyone's replies! Gives me.much to think about and will def get on making some test tiles.. specifically does anyone know if coating the clay in white slip before glazing will stop some of these reactions from happening?Or if a few coats would make the difference? Thanks!

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With dark clays, a good, hot bisque is needed . . . with a hold at top temperature to help burn off gases and impurities that can lead to bloating. Avoid dense stacking of the items in bisque -- give them breathing room.

 

You did not mention what cone you are firing to. Assuming it is cone 6, when glaze firing, try firing to cone 5 and add a 20 minute hold rather than firing up to cone 6 -- you might reduce the likelihood of bloating. The hold will bring your kiln heat work up to cone 6.

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what is the appeal of black clay, figtree?  if you are new at everything ceramic, what makes you think using black clay is a good idea?

 

the skills you need to develop are so vast that the discussion of a clay color right now seems trivial.  since so many people have suggested you not use it, especially as a first clay, maybe you should think hard about why you want to use it.  is there a picture in your head that demands the use of black?  if so, think more about the finished piece of clay and work toward making it in a more user-friendly clay first.  once you have the skill to make the shape, you may decide the black is not necessary at all.  or, at that point, take the advice given above and go ahead and use it.  once you have that skill, everything else will be easier.

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bruce, i know your work and your skill level. i am merely wondering what it is about black clay that appeals to the OP.

concentrating on learning the skills to make pottery rather than the kind of clay would seem the better way to go.

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Here is a long long discussion about a clay body that is black sold in the south east called "Black Raven" 

 

http://community.ceramicartsdaily.org/topic/7599-black-raven/

 

There is a schedule in there that helped me get rid of most of my bloating. I still get some however every now and then. I personally stopped working with the clay. You can see some pictures of the bloating on the pieces I posted. This was many years ago when I was pretty new to it all... If I was new I wouldn't advise black clay to start. It can be really frustrating. 

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Hey thanks Joseph F. It seems I have unknowingly taken on quite the challenge.. I just love the look of black clay! I love the photos you posted! Gah will have a try at it.. thanks for the schedule!

 

There is nothing wrong with a challenge. Just be aware that starting on a steep mountain can be discouraging at times. 

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