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Member Since 06 Apr 2010
Offline Last Active Oct 17 2016 09:36 PM

#102446 Manganese

Posted by JBaymore on 22 February 2016 - 08:48 AM

  The more time I spend in the ceramics community, the more I realize just how much I do not know. :)  


Thank you.


Me too.  One of the beautiful things about ceramics is that you will never get bored... because there is always more and more to learn.  I've got 100 lifetimes planned out. :)





#102407 Manganese

Posted by JBaymore on 21 February 2016 - 06:23 PM



When "granular" manganese dioxide is added to a clay body to create "speckles", it is likely that the material contains the "fines" as well at the larger particles.  So this contributes to the manganese that is in the general body in a "dust" form (as opposed to the true granular... "large" lumps).  A very dark body with a manganese bearing clay or the addition of manganese dioxide also likely has "fines".  So this situation contributes to the potential issues that the general studio dust creates... beyond the 'standard' carcinogen issue with respirable free silica and also the silicosis risk that comes with any clay body.


How exactly this all plays out is very complicated. Occupational health studies available on chronic manganese toxicity have not been targeted at potters and how they use the material and how they typically work (to my knowledge).  So the best we have to go on is trying to make sense of 'what is out there'....and "guestimate" how it might apply to us.  A lot of the info we can get is from industry... and it is sort of not a good model for what we do. 


Additionally a lot of the stuff you hear circulating in the ceramic community is either apocryphal or second hand.  ( ie - "My friend told me that Ralph got lung cancer from breathing clay dust in his studio" .... when what you don't know is that, yes Ralph got lung cancer all right, but Ralph also smoked 2 packs of cigarettes a day for the past 30 years.) 


And in another vein, in some cases, it is based on assumptions about cause and effect relationships that are not there (or are not statistically proven).  Bad science.  ("ie- Bob worked with manganese in the studio... Bob got Parkinson's Disease......... working in the studio with manganese will cause Parkinson' Disease.)


There is sufficient evidence that manganese fume (MnO2) is an issue upon inhalation.  That comes, in our case, from firing in kilns.  Extrapolation says that if the dust from dry clay bodies is of respirable size, then it might very well present the same issues.  But that extrapolation might be wrong too.  There is some evidence that it is also toxic upon chronic ingestion (in larger amounts).  Skin contact thru intact skin appears to not be an issue (mucous membranes and cuts and abrasions aside).


As I mentioned above... you also have to look at intensity (what is the actual exposure level), duration (how long do those exposures last), and frequency (is the exposure infrequent, frequent, 24/7, or what).  That kind of stuff is a 'standard criteria' that must be looked at in determining occupational exposures.  In most studio artists cases... we do not have real data on intensity, we often do not know the real duration.... and the frequency is also often not really determined (example-is your studio in your living space?????).


So lacking hard data (air sampling and the like), the prudent thing most people do is to assume that the exposure is quite significant.... and "play it safe".  Might this be "overkill?  Of course.  Some might call it "hysteria".  Having done some air sampling in my history of doing and teaching this stuff, the exposures likely are less than what everyone assumes they probably are.  But individual circumstances vary SO much that it is hard (and not prudent) to assume that kind of thing.


So maybe it comes down to the "glass half full / glass half empty" stuff.  If something has not yet been proven to be an issue (in the form and way you use it) is it safe?   How one answers that likely determines how one approaches hazards in the workplace.





#102327 Manganese

Posted by JBaymore on 20 February 2016 - 02:55 PM

The potentially toxic properties of manganese compounds in ceramics usage have been known for a LONG time.  The largest hazard is to the potter and it is from fumes (tiny, tiny dust particles) from the kiln gases as the manganese vaporizes during firing.  Of particular concern to the potter is the saturated (gorgeous!) glazes that give such wonderful micro-crystalline surfaces.... because of the very high concentrations of the manganese compounds in them. 


The biggest issues are upon inhalation.


Out of caution (lacking actual leaching studies), it has been good practice to avoid this colorant in glazes used for functional wares for a long time also.


It is important to temper this toxicity information with the occupational health concepts of intensity, duration, and frequency.  Also the form of the chemistry...... oxides, salts, carbonates, and so on... and their bioavailability.  This is not a simple subject.





#102264 Kiln Conversion Updraft Downdraft Chimney?

Posted by JBaymore on 19 February 2016 - 10:20 AM

Among some I'm likely forgetting to write here, the main advantages of forced air ("power") burners over venturi-type aspirating burners or non-venturi "pipe"-type burners are that they:


1.)  are able to cause better mixing of the fuel and air before it actually reaches the wares in the kiln.  So you can get more even atmospheric conditions in the chamber.


2.)  are able to supply 100% or even 100%+ aeration of the fuel.  Even the most efficient and expensive casts of venturi's can entrain no more than about 70% primary air.  And those 'really good ones' are not the typical ones that potters tend to use (industrial units).


3.)  are able to remove the dependency of the entrainment of secondary air by the kiln system itself for complete combustion to occur. 


4.)  are able to somewhat isolate the kiln/burner system from being impacted a lot by variations in the weather and in the stacking of the load.


5.)  are able to reduce or remove the need for a contigious chimney on crossdraft or downdraft designs, thereby cutting construction complications and/or costs.


6.)  help to assure that no unintended fuel gas is left unburned when it exits the chamber.   


7.)  Produce a more uniform atmosphere in contact with the wares when the kiln is adjusted for "reduction" conditions.


8.) typically have better turn down ratios than atmospheric burners. (stability at lowest setting compared to highest setting).






#102205 Finished Pieces Cracking All The Way Through. Help!

Posted by JBaymore on 18 February 2016 - 11:20 AM

Looks like dunting cracks. 


Can be caused by a high thermal expansion (COE) glaze on one side of the form and a low expansion one on the other.  Sometimes if the glazes are just a certain thickness the pieces clay body is strong enough to hold together.  So you don't notice the issue.  But get one or  the other glaze thicker than "normal" past application .. and "boom".  In either case.... not a good situation to have anyway.  Will eventually fail.


Or as Ray is saying above...... a low expansion glaze only on the inside..... can do the same thing.


Sometimes bisque issues can cause this situation if the ware does not have enough oxygen present during the bisque firing (kiln without active local vent, tighter stacking than "normal", faster firing than "normal", lower cone firing than "normal", etc .)  The problem shows up in the glaze fire... not the bisque fire.





#102143 Microwave Safe?

Posted by JBaymore on 17 February 2016 - 10:52 AM

There is a specific accepted protocol for testing if something is labeled "Microwave Safe".  If you don't follow this protocol here in the USA... I'd be careful of formally labeling ceramic wares as "Microwave Safe".  Maybe more like "Can be used in a microwave".







#102038 Kiln Conversion Updraft Downdraft Chimney?

Posted by JBaymore on 15 February 2016 - 08:35 PM

You need a flame retention nozzle of some sort on the end.  Otherwise the turn-down ratio will be terrible and you'll constantly be dealing with back burning or fluffing out.


A pipe cap with multiple holes drilled in it will work as a 'poor man's alternative'.  You'll have to experiment with the pattern and the size of the holes.  Use a close nipple to mount it to the ell you have.


Better to just purchase one... they are more "engineered' than you realize.  Not expensive.





#101980 I'll Never Be A Real Potter.

Posted by JBaymore on 14 February 2016 - 05:55 PM

What exactly IS a real potter?
I think if you are
a: not imaginary, and
b: make pots

You are a real potter.



How do you know that you are not actually an avatar type creation that makes pots in some sort of galactic wide simulation program...and you are just "code"?  ;)





#101846 Claywork While Going Thru Chemo

Posted by JBaymore on 11 February 2016 - 05:54 PM

They should take a list (and MSDSs) of the potential environmental contaminants in that studio (what is used there by everyone), a list of what they will have very close contact with (clay and slip and glaze), info on the kiln effluents that might get into the space (depending on quality of ventilation) and then let their physicians decide.  Make sure the physicians have a detailed and realistic understanding of what ceramists work with (most don't).


I teach this toxicology stuff at the college level.  An Internet forum is not the place for this kind of advice...... as well intentioned as it might be.  Same advice goes to anyone that has any kind of health concerns.


If you want the best advice on this subject,.... get a referral to an occupational health specialist MD, and then get them in consult with the oncologist(s).





#101817 I'll Never Be A Real Potter.

Posted by JBaymore on 11 February 2016 - 10:19 AM

Real potters spiral wedge meatloaf. ;)   Kiku-meaty.

#101679 Couple Of Ash Questions

Posted by JBaymore on 08 February 2016 - 09:06 PM

Simply put, the "real" nuka typically only goes on my 'higher end' pieces.  $400 (+ up) Chawan and the like.  The glaze is labor intensive to make (two different ash sources... one washed), and the currently imported nuka-bai (rice husk ash) is a bit expensive.  To produce it in the volume that I'd need for all or the work that I use "nuka" glaze on......... too much work and would impact price points. 


Example.... If I am making stuff like say more "production oriented" dinner plates....... fake nuka is just fine 99% of the time. 


And by the term "fake", really it just means that it is not made in the "traditional way".  Chemically... it is very close to the same (but not exact... since ash glazes are SO complex).  Particle distribution in the batch slurry is the place that the real nuka and the fake nuka part company...... and that DOES have an impact on the way the glaze melts........ and hence some of the "look". 


Molecular formulas AND raw materials sourcing need to be looked at in "glaze chemistry".  Both have potential impacts. 





#101631 What Glaze Would Give The Effect And Is It Food Safe

Posted by JBaymore on 08 February 2016 - 08:43 AM



Hi and welcome to the forums.


Hard to tell exactly from the picture there, but I think that you are looking at unglazed clay surfaces.  Very common in Japanese work.Looks like a very dark clay body and a lighter slip over that in the one area. 


The slip looks like it is done in a common Japanese approach where it is put on thicker, then fired, then partially ground off after firing. (a time consuming and dangerously dusty process.)


As to the "food safe" question....... you are opening a "can-o-worms" discussion there.  Go to the main forum page and search the term "food safe".  You'll find lots of discussion.  The Japanese have no problems with using this type of ware for food.  For your own work... you'll have to decide AFTER doing a lot of research into the question.  No easy answer there.





#101559 What To Do With All My Early Pieces?

Posted by JBaymore on 06 February 2016 - 02:25 PM

Self editing is a very critical component in learning the art.  Self editing before the clay has been fired... and also after it has been fired. 


Considered and productive self editing... in which you articulate to yourself WHY you are about to reclaim this piece or hit that piece with a hammer.





#101452 Harry Davis,potter,engineer

Posted by JBaymore on 05 February 2016 - 12:16 PM


John, is that because you'd have instructions for building your own studio/ studio equipment on said island?





Yes...... even if you have few tools.


And add to that shipwreck list...... "Pioneer Pottery" by Michael Cardew (Not the similar titled "Pioneer Potter"), and the "Potters Dictionary of Materials and Techniques", Hammar and Hammar.


And great follow up scenario you described there.  SO true! ;)





#101241 What Happened To The Guy Who Wanted................

Posted by JBaymore on 02 February 2016 - 01:40 PM

Speaking here as John Baymore... private party... not as formal CAD Moderator........


This issue is why I think forums of all sorts should require REAL NAMES as user names.  No "hiding".






 Anonymity seems to give some people a license to be rude.  That's one of the reasons I use my real name.  If I'd be ashamed for someone to know I said it, I won't say it