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Crusty

Black Raven

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I have never heard of Black Raven, but I have used a clay by Laguna that is black at C6 electric.  I tested 20 glazes on it and wasn't happy with any of them,  I have used it for a wrought iron look.  Denice

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I have  used Black Raven and had problems with the glaze bubbling. I found later that the firing is done differently, I don't remember about the bisque firing but the glaze is fired to cone 6 with no hold. Check with one of the glaze companies or your local store.

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a SLOW 04 Bisque is required and your correct about a no soak ^6 - i have 15 test tiles  and a couple pieces with slip on them, in for tomorrows Bisque firing.. It has something in it thats gritty, pretty small pieces but i can feel it.. I can feel it on the wheel in the slip that builds up... im thinking its a colorant because a clear glaze will turn it green and brown.. i am really interested in using white and red slips on it...

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Oh my goodness. I have been wanting to use a black clay for a long time but I couldn't find any suppliers in my area. I searched Black Raven and there is a supplier 30 minutes from my house in Stone Mountain GA!

 

Definitely going to have to try this stuff. I have been wanting to make mugs with the top 1/4 of the mug glazed and the rest unglazed. 

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Hi, This is Tom in Atlanta.  Black Raven is mixed by Stone Mountain Clay.  They are a very knowledgeable family with a long history in the ceramic supply business, and great folks.  Black Raven clay is a very metal rich clay and a little finicky.  But so is any "Black clay"  from a variety of suppliers, I.E. Laguna, which I have used.  Yes a slow bisque with a "hold" I believe around 1500 F.  for 10 minutes, fired to 04.  I have found that the clay can bloat, again as other suppliers clay can do.  I finally after a number of test firings, now fire it to cone 4, and use colored slips, underglazes, with a cone 06 dipping glaze for shine. There is a lot of gas in this clay so any fast firing will cause problems, including glaze.  I have programed special ramps into the computer specifically for this clay. This is a exciting clay to use, I do special pieces with it and don't attempt to run production work with it.  But love the unexpected results.  My work surely does not look like electric firing.  I would suggest you give yourself some time to run some tests and see where that takes you...If you have questions, my email is tzwierlein@lovett.org    Tom

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Picked up my #100 of black raven. 

 

First Impressions:

 

1. The clay is very soft straight out of the bag. A lot of times I have to wedge the clay to get it easier to work with. This wasn't the case.

2. It is a dark brown color like milk chocolate Hersey bars or something in the wet phase. It dried on my wrist as I was throwing and this was like a grey charcoal color.

3. It is sticky as all get out. Which doesn't really bother me, but I know it has bothered others on this forum before. Really hard to clean it off your hands to quickly lift off a pot. It also does have some minor grit in it like Crusty stated, not sure what it is either, but its very minor. I find I can still get a really smooth finish with a metal rib.

4. Throws really well. I threw a bunch of cylinders and a few bowls. All of them threw easy and I even tried to push the bowl till it collapsed. I added water and pulled and shaped it numerous times. Held together well.

 

I will keep updating as I progress, but so far I like it.

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I read about the safety problems of firing clays with maganese dioxide. On the manufacturers website it says the clay has less than 1% manganese dioxide. I also fire with a vent to the outside of my house. I don't think I should have any other worries should I?

 

You have me all worried now. I have read on the problems, and most of it is breathing in greenware dust or sanding greenware. The actual dangers of working with wet clay with less than 1% is very low.

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There was a good explanation by John Baymore recently: Can't remember if if was here or on FB.

I can't find it now: hopefully he will appear here and copy and paste from the other thread or give a link to it.

I know that it is not the wet state: it is very small particles that are sent into the air during firing that are the most potentially hazarous

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Don't ask Baymore to copy and paste  :P

 

Little search found

 

The granular manganese added to clay bodies is not JUST about the granular factor.  It is true that in 'bug lumps'... the issue of the available pathways for the material to get into the human body are pretty much nonexistent.

 

However, granular manganese is often packaged with what are called "fines".  Fines are the dust fraction.  That dust is typically not cleaned out from the large pieces when the clay body is mixed up.  So there is very likely a TRACE of very fine MnO2 material in any body containing granular manganese.  That is in the general dust that the body gets into the studio environment.  Likely this is a very low level.

 

The real potential issues are from the FIRING of manganese containing bodies. 

 

Manganese likes to "fume" from high fired wares.  Fumes are typically misunderstood by many potters.  They are not gases..... they are actually very tiny weenie, isty-bitsy dust particles.  So tiny that the molecular vibration of the air molecules will keep those particles suspended in even still air for 24 hours or more.  These escape into the kiln atmosphere.  If that kiln atmosphere escapes into the studio rooms, then some manganese fume is going with it.  THESE particles are highly respirable, and  therefore represent a high toxicity concern.

 

There is an interesting problem hiding here.  Most fuel fired kilns utilize significant draft flow,  and any stuff released into the kilns' atmosphere is typically mostly vented outside the studio spaces.  So manganese fume, if present, would mostly be picked up and vented elsewhere (if the kiln is installed and operated properly).  But electric kilns do not have this large volume draft flow.  And for what type of firing do we typically see granular manganese added to bodies?  Why... electric oxidation firing.... to add interest and variation to the clay body.

 

So the proper venting of electric kilns that are used to fire manganese containing bodies becomes of paramount importance to the POTTER.  If you don't KNOW that the vent system installed on your electric kiln is working WELL...... then you are "playing with fire" (pun intended  ;)).

 

The second issue with the firing side of using granular manganese in clay bodies potentially applies to the CONSUMER.

 

Granular chunks of manganese concentrate a lot of the material in one place.  When you then put a glaze OVER this little spot, that MnO2 bleeds into the glaze lying right over it and colors it.  Nice.... great visual texture.  However that large saturation or OVER-saturation of manganese in the glaze at that point likely is at a level that will not hold all of the MnO2 in solution during the cooling phase.  So if you look at those lovely little speckles under a microscope, you'll notice that the surface is often micro-crystalline....with some Mn stained alumino-silicate forming on the surface.  This manganese is NOT bound well into the glaze melt... and can easily leach out.

 

How much this amounts to as a potential toxin for the user of the wares is impossible to predict.  It depends on so many variables and factors.  The particular clay body and how much manganese granules per square inch are on the surface, the nature of the overlying glaze, the thickness of application of that glaze, the firing cone, other colorants present, and so on.  The only way to accurately assess if this is an issue is a routine of sampling of the production and actual lab testing to KNOW the answer.

 

The comment above from bciskepottery about KNOWING your materials is probably the MOST important comment in this thread.  It is very easy to take 2 or 3 pottery classes, buy some equipment, and set up and start making and selling pottery.  It take YEARS of study and experience to actually know what you are doing.  Clay is long.... life is short.

 

best,

 

............................john

 

 

Thread http://community.ceramicartsdaily.org/topic/7487-manganese-dioxide/?hl=manganese

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Okay, so I am a rookie here, but his post is about Granular Manganese. Which is a much more concentrated source of manganese compared to the dioxide.

 

All this has me worried and I am not sure if I should even continue down this route with the clay. I think after reading through that entire post. I will just abandon ship on black raven.

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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.

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Granular Manganese

In ceramics, it is used primarily in clay and glaze to achieve dark brown or black fired speckle. This is the same material as manganese dioxide powder, it is simply not ground as fine. Typically a 60-80 mesh material is used in amounts around 0.2-0.3%.

 

 

The threshold limit value for dusts of manganese metal and inorganic compounds actually proposed by the ACGIH is 0.2 mg/m3,as total dust.

http://digitalfire.com/4sight/hazards/ceramic_hazard_manganese_inorganic_compounds_toxicology_317.html

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Ah, I was just a little confused as I thought you were saying granular was a different substance to the dioxide.

 

I don't really like using the stuff as I haven't found it very useful in any of my glazes yet and the risk doesn't really outweigh the results. Cobalt on the other hand, dangerous but beautiful.

 

I did make a blackish clay body using black iron oxide. I think. I can't really remember as it was a long time ago and I gave up quickly. Could have been red iron oxide.

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A fun and versatile way to get the look of a black clay is to make some slip with the clay you are using, tint it with black mason stain and put that on the freshly made pot.

You can then  scratch or scrafitto through that to the lighter clay below for another decorative element.

It is generally cost prohibitive to tint a lot of clay so by just tinting a slip of it, it stays affordable too.

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