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JBaymore

Member Since 06 Apr 2010
Offline Last Active Yesterday, 09:20 AM
*****

Posts I've Made

In Topic: Working With Kiln Bricks. Wet Or Dry?

03 March 2015 - 10:24 PM

Hard bricks can be wet down also... but it only gets the surface dust.  If you are cutting or grinding them.......... wet saw or serious ventilation and respiratory protection.

 

If the teacher won't let you...... you might want to find another location to work.  It likely says a lot about other H+S practices there.

 

best,

 

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


In Topic: What Causes Glaze/clay 'tide Mark'?

03 March 2015 - 04:34 PM

The finger wipes are thinning the residual glaze coating on top of the body.  This thin glaze coating is on a stoneware type body, so the interaction of the glaze and clay body (called the interface zone) will exist.  This is where the body grows crystalline materials into the glaze, and the glaze "eats" materials out of the body. 

 

In this situation there is little glass forming there... and the percentage of the body materials that are "in" the super thin glaze layer is high relative to the glaze's normal composition.

 

Two things are happening there.  One is that the alumina from the body is raising the Al2O3 content of that glass there.  That will tend to influence color rendition out of any oxides present.  Secondly, even white stonewares contain traces of iron oxide. 

 

The combination of a high alumina glassy phase and small amounts of iron oxide cause iron to go to the reddish color phase.  Hence the reddish brown marks. 

 

Same reason real shinos blush with that red firecolor on the thin spots on the high alumina refractory bodies they use.  Difference her is the presence of calcium and magnesium...... which dull the iron colors more toward the browns.. 

 

best,

 

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


In Topic: Working With Kiln Bricks. Wet Or Dry?

03 March 2015 - 01:46 PM

When I am working insulating firebricks they are always worked wet.  Brick and fiber dust is "bad news".

 

Isn't going to do much for the chipping factor.  Work slowly.

 

best,

 

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


In Topic: New Work -A Bit Different For Me

03 March 2015 - 12:25 PM

Except you New Englanders you signed up for it long ago. ( I spent 1 winter in New Hampshire) cured me straight away at 15 years old.

 

Hey... I resemble that remark! ;)

 

best,

 

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


In Topic: What Causes Glaze/clay 'tide Mark'?

01 March 2015 - 09:38 PM

It is volatile compounds in the glaze are fuming the body along the border.  The common factor in the neph sy and the wood ash fusion buttons is high levels of sodium.  Potassium also does it.

 

You can't see the same stuff coming out of the larger expanses of the glaze surface and going into the kiln atmosphere... because it won't "mark" the glaze surface it is coming from.  But the bare body acts as a "tracer" for this stuff.

 

Almost all high wood ash glazes do this.  Ditto to high soda ash shinos.

 

Less common at cone 6 range than at 9-10 due to the reduced volatility of the soda and potash compounds.

 

best,

 

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