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blacknapkins

Midnight Black II from Seattle Pottery Supply— firing

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Just got some of this stuff. I'm wondering what will happen to it if I fire it at cone 6. It's rated specifically as an 04-5 clay.

 

Will it totally completely melt or just slouch a little or what? I only bought 25lbs and I have a 10cu/ft kiln that I won't fill up with just this.

 

I would just be making mugs and teacups, pretty structurally sound cylinders without any big peripheral things that can't suppor tthemselves.

 

THanks guys

 

Eric

 

PS I'm really new to this stuff. : D

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I assume this clay contains manganese. Get the MSDS from the manufacturer to find out for sure. Assuming it does, read up on manganese toxicity and safety before using the clay. It is beautiful.

 

Most often the biggest problem in over firing clays containing manganese is bloating, so you may find ^5 is as far as you can take it, especially if your kiln is not perfectly calibrated. If you want to try pushing it to ^6, put a plate under it, something made out of a safe-to-^6 clay.

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Just got some of this stuff. I'm wondering what will happen to it if I fire it at cone 6. It's rated specifically as an 04-5 clay.

 

Will it totally completely melt or just slouch a little or what? I only bought 25lbs and I have a 10cu/ft kiln that I won't fill up with just this.

 

I would just be making mugs and teacups, pretty structurally sound cylinders without any big peripheral things that can't suppor tthemselves.

 

THanks guys

 

Eric

 

PS I'm really new to this stuff. : D

 

 

The cone range is way too broad. The cone a clay should be fired to for maturity should be be one cone or at most 2 cones. Had it been rated cone 4-5 that would be fine but 04-5 can't be a maturity range. That doesn't mean that you can't fire it to 04 and be happy with the piece (as long as it isn't supposed to hold a liquid and you know it is under fired) but it isn't mature at that cone. (Or, if it is then it is it should be a puddle at cone 5.) Usually, a cone 5 clay fires to cone 6 with no problem but what Diane says above is important when using a black clay. Just test it first. Put an unglazed cylinder of it in a cone 6 firing. It's not going to melt. If it doesn't bloat then you know it is probably a cone 5-6 clay and you should test for leakage by filling it with water and leaving it overnight on a piece of paper.

 

Jim

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Oh, and tell Seattle Pottery Supply that their cone range for that clay is misleading nonsense that is a big disservice to their customers.

 

Jim

 

 

Years ago they told me that "04-6" etc indicates first the ideal bisque temperature and second the maturation temp. I always just thought this was a standard way to label a clay body but people on here have been confused by it so it must be a Seattle Pottery thing.

 

Thanks everyone else for the information. It gives me a ballpark of expectation without having to worry with meltdown!! : )

 

I will post results in case anyone is interested : )

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Oh, and tell Seattle Pottery Supply that their cone range for that clay is misleading nonsense that is a big disservice to their customers.

 

Jim

 

 

Years ago they told me that "04-6" etc indicates first the ideal bisque temperature and second the maturation temp. I always just thought this was a standard way to label a clay body but people on here have been confused by it so it must be a Seattle Pottery thing.

 

Thanks everyone else for the information. It gives me a ballpark of expectation without having to worry with meltdown!! : )

 

I will post results in case anyone is interested : )

 

 

Actually, that would be a good way to label clay as long as it is made obvious that the 1st number is bisque and the 2nd is maturity. So, no, firing it to 6 will not melt it but just test it because, since it is a black clay, it may bloat at 6.

 

Jim

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Oh, and tell Seattle Pottery Supply that their cone range for that clay is misleading nonsense that is a big disservice to their customers.

 

Jim

 

 

Years ago they told me that "04-6" etc indicates first the ideal bisque temperature and second the maturation temp. I always just thought this was a standard way to label a clay body but people on here have been confused by it so it must be a Seattle Pottery thing.

 

Thanks everyone else for the information. It gives me a ballpark of expectation without having to worry with meltdown!! : )

 

I will post results in case anyone is interested : )

 

 

Actually, that would be a good way to label clay as long as it is made obvious that the 1st number is bisque and the 2nd is maturity. So, no, firing it to 6 will not melt it but just test it because, since it is a black clay, it may bloat at 6.

 

Jim

 

 

So, bloating sounds pretty obvious but I've never even heard of this before. I'm going to give them a ring tomorrow and find out if there's manganese in this and I will report back.

 

Thanks guys.

 

It feels great to be new to pottery. : )

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That clay body is certified non toxic. Even if it has manganese it's safe to use. Just follow typical safety procedures to reduce dust.

 

 

Yes, it does have manganese in it and I also found some ancient (1994) pdf that said it was non-toxic on google. Sounds a little contradictory. I actually realized today (oops) that the label on the clas states clearly that it contains manganese and suggest wearing a respirator and gloves to minimize exposure.

 

What safety precautions do you recommend?

 

I think working on the wheel with a respirator and gloves would be absolutely horrible. In fact that's half the reason why I quit my job as a silversmith/goldsmith/casting shop.

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Your main concern is inhaling dry/powedered silica, manganese. Working in a wet state should be okay without putting on a respirator and gloves. I use a similar Standard clay body (266) that also contains manganese to get its black color. Working with dry clay, you might want to take precautions, e.g., drying clay to make a slip, sanding bisque ware, etc. Also, working with manganese dioxide in glazes requires respirator. Some folks are sensitive/allergic to metalic oxidies in clay bodies and glazes; if you develop an itch or rash, you might need gloves.

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