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JBaymore

Member Since 06 Apr 2010
Offline Last Active Today, 09:15 AM
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#106103 Help - My Kiln Shelves Melted!

Posted by JBaymore on 02 May 2016 - 10:41 AM

If it is an analog meter.... that increase in inaccuracy with increasing temperature is a well known normal aspect of the system.

 

best,

 

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




#105988 Large Platter Broke In Half In Bisque Firing. Anything To Do With It?

Posted by JBaymore on 30 April 2016 - 11:08 AM

Alpha/beta quartz inversion is at 1063 F.  It is sudden... at 1062 nothing...... at 1064 expansion.  Reversible on all crystalline silica (not glassy phase nor the cristobalite form).

 

Given the inaccuracy of most pyrometers folks are using... (not to mention thermal lag in the load) the safe bet is to go slowly up and down between about 1000 F and 1100 F.

 

best,

 

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




#105593 Simple Wadding For Supporting Pots In Electric Kiln Glaze Firing

Posted by JBaymore on 23 April 2016 - 07:41 AM

I think you are maybe mis-reading the above posting.

 

One particular wadding mix is 50% alumina hydrate and 50% EPK.  Does that help?

 

It is not 50% EPK wadding MIX that is half of the recipe.

 

best,

 

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




#104506 How Often To Change Filter In Mask?

Posted by JBaymore on 31 March 2016 - 09:42 AM

Assuming that you don't somehow physically "puncture" one, they do not start to "leak" ingredients thru to your breathing zone.  What happens is that they clog up the miniscule pores (that act as the filter).  So breathing slowly and steadily gets more and more difficult.

 

They are pretty cheap, so changing them regularly really is not a big deal. 

 

best,

 

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




#104389 Qotw: Seconds Getting Firsts Anybody?

Posted by JBaymore on 29 March 2016 - 10:06 AM

While "never" is a pretty absolute term, and memory is not a sure thing... I think I can say I never did this deliberately.

 

HOWEVER...... and that is a BIG "however"......... if I look backward from my current vantage point of experience, many things that I sold in the past (particularly the long distant past) I now would have considered "seconds" or "subs" (below aesthetic standards). :(  

 

best ,

 

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




#104377 Silica Dust In The Mainstream News

Posted by JBaymore on 29 March 2016 - 07:56 AM

JBaymore,

Have you heard any feedback from the education community on how this will impact clay studios?  We have what I would call exceptional filtering in our dry material area and mixing room plus we require full coverage masks in the room...but the 50 micrograms per cubic meter standard may pose a real challenge!
 

Paul

 

Paul,

 

I of course can't speak for the whole industry.  It's a topic of discussion amongst a few of us... but nothing definitive.  I'm sure it is going to start being looked into pretty fast at a lot of places.  And unfortunately, some places have totally ignored this kind of stuff in the past ... and likely will continue to do so.

 

I'd say it is time to go into the stock market and invest in companies that make PM 2.5 air sampling units.  I think a lot of testing is going to be starting shortly in lots of places  ;) .

 

My college's mixing areas are pretty "state of the art" (individual stations with slot hoods, formal engineering done on the design) so that is not a problem for us.  Kiln room can suck the pots out of the kilns and have us unload them on the building's roof.  The place that we'll be looking is likely the general classroom studio spaces to check the air turnovers there.

 

Everyone will be 'feeling their way' with this, I think.

 

The TechnoFIle piece in CM this month on top of this from OSHA is a 'double whammy'.  There is one data point in that piece that I am researching a bit more info about (point H on the graph) .  If it is truly accurate as described... it is pretty scary.

 

best,

 

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




#104253 Silica Dust In The Mainstream News

Posted by JBaymore on 26 March 2016 - 11:26 AM

FYI for us potters:

 

Note the magnitude of the standards decrease.

 

http://www.nbcnews.c...5-years-n545201

 

best,

 

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




#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