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JBaymore

Member Since 06 Apr 2010
Offline Last Active Today, 02:58 PM
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#104245 Trouble With Red

Posted by JBaymore on 26 March 2016 - 09:23 AM

 I was looking for the how close to the rim something can be used guidelines but didn't find them. I do a lot of hand painting with Underglazes then clear glazing on mugs so this is an area I am particularly interested in.

 

Lip and rim:  http://www.astm.org/Standards/C927.htm

 

Considered the top 20 mm both inside and out.  -SGCD- Washington DC.

 

best,

 

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




#104216 Trouble With Red

Posted by JBaymore on 25 March 2016 - 06:26 PM

If cadmium compounds are present (likely in this kind of a red), in a slip, glaze, underglaze, overglaze, etc, on food contact ware... potters are bound by the US FDA (and California) laws.  Not just the glaze.  To comply with those you have to test to know that the levels are below the thresholds (which differ for different types of forms).  That is why the manufacturers 'hedge their bets'.  They don't indemnify the users of their products.

 

A glaze coating over a slip/underglaze, stain etc. doesn't assure that the underlying material is somehow 'isolated' from the surface of that glaze.  Particularly at elevated firing temperatures where the interface layer is pronounced.  Also the application thickness of BOTH components could then be very involved in any potential issues with release. 

 

The only way to KNOW is to have the combination tested in a lab.  99.999999% of the time it likely will be fine.  But the laws are the laws.  People should know about them.

 

Encapsulated stains are new enough that the laws have not caught up with them (yet).  If they ever will.

 

Because MANY people read these threads... of varying experience levels...... I post this kind of stuff.

 

Red can be beautiful.  But there is stuff that people should also know about (in case they don't) beyond the 'Mark 1 Eyeball Test'.

 

best,

 

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

 

PS:  Yeah... that MSDS is a joke.  (Another whole subject!) Wouldn't download when I checked earlier........ had just upgraded to adobe Reader DC...... which screwed up my browser's ability to get pdfs.




#103915 Gas Vs. Electric- An Alternative View

Posted by JBaymore on 21 March 2016 - 09:20 AM

Since FeO is a flux on silica, if the kiln is fired in reduction, and the reduction occurs when the body is still gas permeable to the CO molecule, AND there is some level of Fe2O3 present, then the added flux would likely produce a more fluid melt.  This impact might be what they are talking about.  Heavily iron fluxed glass in a body can promote brittleness... so generally too much is not a good thing even though it can decrease Apparent Pororsity figures.....so I can't believe that they are talking about that kind of level.

 

Never tested the two directly against each other for something like MOR.  (same body in electric and reduction gas)

 

best,

 

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




#103700 Who Is Attending Nceca This Year? (Spring 2016)

Posted by JBaymore on 17 March 2016 - 06:34 PM

Opening Ceremony (They are expecting to break 7000 people!)

 

gallery_1543_1159_74182.jpg

 

 

View to my right....... I'm in the center of the hall........ thre is a matching crowd to my left (and more in the back of the room):

 

gallery_1543_1159_136823.jpg




#102640 Who Is Attending Nceca This Year? (Spring 2016)

Posted by JBaymore on 26 February 2016 - 10:20 AM

Welcome to the forums, Carole.

 

You have to ask yourself how much appeal that the NCECA program other than looking at / trying wheels might offer you....as you evaluate that 12 hour drive. 

 

If you have not gone here...... you can check out what is being offered: http://nceca.net/2016-kansas-city/

 

Most people seem to find NCECA conferences pretty amazing.  There will be about 5000 people there as crazy about clay as you are ;) .

 

best,

 

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




#102565 Qotw: Can You Do Whatever You Want To A Bought Piece Of Art?

Posted by JBaymore on 24 February 2016 - 10:30 AM

I am happy to say: this is the first time I heard the story about the man destroying a bit of beauty and history.

 

 

 

Ai Wei Wei...... People's Republic of China.  Look him up.  Political Dissident.

 

best,

 

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




#102520 Functional..foodsafe.

Posted by JBaymore on 23 February 2016 - 12:20 PM

First of all it is about the FORM of the chemistry as to the potential toxicity and the particular routes of exposure.  If you just think about "Barium" sort of generically as a single thing, you likely need to narrow things down a bit.

 

An example:  Barium CARBONATE is a relatively toxic substance upon ingestion (soluble in stomach acid....not so much in water).  However, Barium SULPHATE is not and is used in gastrointestinal x-ray procedures.  The Ba+2  ion and the very soluble in water chloride, nitrate, and hydroxide forms are well known to be toxic. 

 

Once again.. the main hazard from barium carbonate is to the potter handling the raw material (mainly inhalation and ingestion).  See MSDS for what you use for ALL materials.

 

Chronic exposure to low levels of Barium OXIDE....... that which is what is left in the glassy matrix after barium carbonate is fired (but see below)...... well.... not much info or studies on that very specific issue, which is what we are concerned with when we talk about that nebulous term, "food safe".  How well tied into the matrix the barium ions are...... only testing will tell for a specific formulation, application method, and firing profile.

 

Barium oxide is known to be toxic... but typically in acute situations.  Chronic long term studies... typical of leaching into food stuff....... have not found too much info.  Studies say that only about 5-30% of the total barium compounds that are ingested are actually absorbed into the body.  So leaching would likely have to be substantial to be of a huge concern. The chronic long term MRL (Minimum Risk Level) is set by most studies as 0.2 mg/kg/day.  For a human of about 175 pounds / 79 kilos that would be ingesting 158 mg per day for at least a year. 

 

Note that barium carbonate sometimes has some issues in dissociating into barium oxide (what acts as a flux) in firings.  When that happens you have little "flecks" of barium carbonate particles suspended in the glaze melt.  In THAT case......... you are dealing with a much higher likelihood of leaching of a clearly toxic substance into foodstuffs.

 

Formal lab leaching tests would be in order.  As a minor secondary flux, it is likely in my opinion that such a level of BaO in a glaze is not an issue.  Too little of it there to be enough to cause issues.  Stuff like those beautiful, gorgeous, barium blue matts?  That is where some real issues very likely would lie.

 

Prudence issues again here like in the manganese discussion elsewhere.  Glass half full or half empty?  If you don't KNOW that a hazard actually exists, does that make it safe?

 

best,

 

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




#102491 Who Is Attending Nceca This Year? (Spring 2016)

Posted by JBaymore on 23 February 2016 - 12:15 AM

First of all ....don't miss the K-12 exhibition.  Always stupendous.

 

best,

 

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




#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. :)

 

best,

 

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




#102407 Manganese

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

Roberta,

 

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.

 

best,

 

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




#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.

 

best,

 

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




#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).

 

 

best,

 

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




#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.

 

best,

 

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




#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".

 

http://www.astm.org/...dards/C1607.htm

 

best,

 

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




#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.

 

best,

 

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