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Black Raven


Crusty

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you would have loved the studio at rising fawn georgia.  charles counts had trash cans full of slips and dipped everything all the way.  carving through it is the best fun of all.

 

when you are ready to experiment with color, just add some mason stains, carbonates or oxides to the chopped up clay.  you can see the collection of colored slips on my wheel table and a result on the avatar.

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Well, I finally did it. After about 5 months of testing small doses of black clay in my attempt to find a correct bisque for my wants and needs I have found a schedule that completely removes the bloating from my black clay. I should also add that I increased the oxygen in my kiln by increasing my vent intake to about 60% closed, and I drilled a 2nd hole in my kiln lid. My little kiln just needed more air. Also my glazes look much better now that I added the 2nd hole. Damn kiln was built so well it wasn't getting any oxygen.

 

As promised if I found a bisque schedule that would solve the bloating issues I would post it. So here it is:

 

Step  Deg/Hr  Temp  HoldTime(hrs:min)

1       80          180     2:00 - (if your clay is 100% bone dry you can skip this hold, or reduce to your needs)

2       150        600     0:00

3       240        1250   0:00

4       100        1500   1:00

5       150        1650   0:00

6       200        1850   0:00

7       108        1975   0:10

 

This bisque schedule focuses on a very slow burnout of the organic and inorganic carbons, so good for those dark bodies that I like. It is a slow bisque and takes about 18 hours to complete. !

It is the 1 hour hold at 1500 that is the key to stopping the bloating. SO many electric kiln bisque schedules completely miss this step. And often it does not matter with brand new commercial clay which has little or no organic stuff in it. The proble often does not show up until you start using recycled clay or doing other funky stuff to your clay body....

 

Plus having MORE oxygen in the kiln not less.

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  • 2 weeks later...

I will do a search, but at less than 1% should i really be worried? I have a vent that goes directly to the outside of my house, and no one is in my garage when my kiln is firing. I dont even pot while the kiln is going. I am not a production potter so I can just relax while my wares fire.

 

 

I think the term granular manganese means 'big chunk of manganese dioxide' 

 Totally, thats what I was saying in the above post. Granular means like ball or small ball of something. Where the dioxide is a much purer form? . So a lot of the problems in his above post talks about specific parts of the chunks of granular manganese leeching through. Either way, I dont want to have any side effects with dust or anything. I am 30, and there are plenty of beautiful clays to work with, and I have enough health problems as it is.  Besides I doubt I will ever be a production potter anyways. So I will just find another clay body to work with. I was just really excited to have a black clay. I have wanted to work with black clay since I started.

 

 

 

I think the term granular manganese means 'big chunk of manganese dioxide' 

 Totally, thats what I was saying in the above post. Granular means like ball or small ball of something. Where the dioxide is a much purer form? . So a lot of the problems in his above post talks about specific parts of the chunks of granular manganese leeching through. Either way, I dont want to have any side effects with dust or anything. I am 30, and there are plenty of beautiful clays to work with, and I have enough health problems as it is.  Besides I doubt I will ever be a production potter anyways. So I will just find another clay body to work with. I was just really excited to have a black clay. I have wanted to work with black clay since I started.

 

Manganese in Clay Bodies

Manganese materials (powder and granular) can be ground from a variety of ore materials, thus the powder is not a pure manganese oxide. While they are often considered a nuisance dust the ores often also contain significant amounts many other compounds like barium, lead, quartz.

 

Among potters and hobbyists, the most significant use of manganese is in metallic raku fired glazes (20% or more). However high amounts of manganese dioxide can also be used in bodies for dark grey and black colors (up to 10%). These can likewise produce metal oxide fumes that can be very harmful. Unventilated indoor kilns pose a significant threat but standing downwind or close to outdoor kilns can also be a serious hazard.

 

Before classifying bodies containing manganese granular (to create a speckled fired surface) as dangerous the situation must be put into perspective. Such bodies contain only about 0.2% of 60-80 mesh manganese granular. The vast majority of particles are encapsulated within the clay matrix. Most of the tiny percentage of particles exposed at the surface are engulfed by the glaze. All of the tiny number of particles that actually bleed up through the glaze to either near or at the surface have been significantly diluted and stabilized by the glaze melt that surrounds them. Thus the total area of leachable manganese glass on a functional surface is extremely small.  (from Digitalfire,com)

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Crusty and Joseph,

 

So I've read through this whole thread tonight because I'm going to SMC Saturday and wanted some black slip however they only have it made from Black Raven.  My plan is to try it over 202 and 290 stoneware for scraffito.  Have either of you used it as a slip over other SMC clays?  When used as a slip does it need Joseph's firing schedule he figured out for when it's the clay body to prevent bloating?

 

Thanks!

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the descriptions of scraffito were written many years ago.  slip was the easy, cheaper thing for potters to use.  the explosion of factory made underglazes is recent  and today, people have money enough to buy things earlier potters would have never thought of.

 

yes, i use lots of different colors of underglaze and carve through it all.   what are you thinking?  even if you apply a ton of underglaze while the pot is still damp, you are only thickening the layer of color.  you will put your tool into the clay under the color.

 

 i do not understand the question.

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What we had done in class was a single layer of slip over the soft leather hard pot.  Let the slip dry then draw through the slip layer only ... not actually cutting into the clay.  But it sounds like you are saying that the underglaze is not thin so can draw through just that layer.  Thanks!

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I have never used Black Raven but I have used a similar clay that Laguna has.  None of my glazes came out good and the texture of the clay is to coarse for me.  It does look like wrought iron at C6 so I have used it for some sculptural pieces.  I'm glad I only bought 50lbs.     Denice

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After I had posted my original request for info to Crusty and Joseph I did some additional reading on black clays.  In general they seem to be difficult to use.  Since I'm not really after a black clay per se, I think I'm going to go with oldlady's suggestion of mason stain and slip.

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Judy go with the underglaze as oldlady said. Black raven is a huge pain. Finding glazes that look good on it is very difficult and it stains everything it touches. I have ended up using most of mine for large flower pots. I bisque it, then in the same firing take it to cone 6. With no glazes the black flower pots look nice in my backyard.

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judy, whatever you add to the clay itself once the pot is made, comes out as thick as you want it to.  

 

make slip as thin or as thick as you decide.

 

put as many layers of underglaze over the clay as you decide.  

 

cut into the clay as deeply as you decide.

 

the beauty and the problem with all this is that it is your responsibility to do what will work to produce the result you desire.    i am still having problems understanding the question.  i hope i have not confused you.

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Don't you love having to communicate electronically? I have always been under the impression that underglazes were thin like watercolor and therefore would not have enough thickness to draw through without also carving into the clay. For several of the designs that carving would be an added bonus. But I have one I'd like to do where I wouldn't want any texture just the drawn design. I think you've clarified the path I want to take...color my slip with black Mason stain then I can choose how deeply to carve based on the design. At this point I'm not looking for all the great variety of colors possible with underglazes but just the straight black/white of traditional sgraffito. If I can master that then I can add more colors.

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ok, i guess we want to work differently.  i WANT to carve into the clay.  that is the whole point for me.  see the avatar at the left.  i use a white clay and want the contrast of the white lines on the black background.  maybe you can post a picture of what you want to do once it happens because it is such a foreign thought for me.

 

black mason stain in white slip is going to come out grey.  that is why i suggested underglaze.  it is black.

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