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Member Since 15 Mar 2013
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#106339 Metal And Arcing In An Electric Kiln

Posted by jrgpots on 05 May 2016 - 02:15 PM

If the nails were galvanized, the galvanized material will "burn off." It kind of looks like sparking.



#105351 Attempt At The Vintage Look

Posted by jrgpots on 17 April 2016 - 10:04 PM

I just finished this plate.  I wanted an old or vintage look as if it were from the turn of the century.  The clay is a buff colored and reclaimed, cone 5 reduction.  Barnard's slip was applied to the greenware with a mild sgraffito patterned. Licorice black was applied in the crevices then and a local clay glaze was applied to the piece. 


Does it look vintage to you?

Is it successful?



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#104643 Planning For Shrinkage

Posted by jrgpots on 03 April 2016 - 03:53 PM

So find the diameter of you measuring tsp (assuming a sphere shape spoon) and divide by 0.6815. This will give you the diameter of you greenware spoon.

You mean volume, not diameter, right?
The volume of a sphere is 4/3 x pi x r3. So you can devide the volume by 0.6815...True.

And, since the volume of a sphere equation has only 1 measurement of distance, the radius, you can divide the radius by 0.6815 and get to the same place. The radius may be hard to measure, so measure the diameter instead. It is easier.

So the Answer to your question is: you can get the right adjustment by dividing the volume or the diameter. It will end up the same. This is unique to the sphere.

If you are making a cylinder, divide the volume by 0.8615.
You could divide the height by 0.88 and the diameter by
0.7744, which is 0.88 x 0.88. This is because volume of a cylinder is..... pi x r squared x height.

As a side note, this is why mugs proportions look different after firing. The fired height will be 0.88 of its prevoius height while the diameter will be 0.7744 of its diameter.


#104608 Planning For Shrinkage

Posted by jrgpots on 02 April 2016 - 10:57 AM

It would be really hard to work with clay on the moon  since it would loose all of its water content even before the first firing. :P   But what a great question...I understand that the ryolithe on the moon is very abrasive.  I would hate to throw with that type of clay too.   Some of you guys who like to "throw dry" might even struggle.  I wonder if you had a pressure controlled environment with O2 on the moon, would it be easier to pull a cylinder in the decreased gravity?  would the clay tend to fly off the wheel more?..... Babs, you started a whole new set of questions someone could ponder over for years... B) .




#104594 Planning For Shrinkage

Posted by jrgpots on 02 April 2016 - 12:28 AM

Just for fun, I calculated the needed volumes (in mls) of greenware mug sizes to make 8, 12, and 16 oz fired mugs. Mind you, I calculate these based on my math and have limited experience on the wheel.

8 oz fired cup.... 12% shrinkage.....347.18 ml greenware.
15% shrinkage.....385.28 ml greenware.

12 oz fired mug.... 12% shrinkage ....520.75 ml greenware.
15% shrinkage.....577.90 ml greenware.

16 oz fired mug.... 12% shrinkage.....694.35 ml greenware.
15% shrinkage.....770.56 ml greenware.

Mark, Marcia, John, Neil, and others with the experience do these values sound right?

#104593 Planning For Shrinkage

Posted by jrgpots on 01 April 2016 - 11:26 PM

Let me throw a wrench in the calculations.
1. As mentioned the length will shrink by .88.
2. But, the area will shrink 0.88 x 0.88 or 0.7744.
3. A Volume will shrink 0.88 x 0.88 x 0.88 or 0.6815.

What does this mean?
1. It means that the volume of 1 tsp will shrink to 0.6815 of its volume after firing.
2. If you want to make a tsp volume after firing, you will need devide your prefired volume by 0.6815.

Now let's assume you want to make measuring spoons in a half a sphere shape. This means the diameter of the greenware spoon needs to be 1.136 larger.

So find the diameter of you measuring tsp (assuming a sphere shape spoon) and devide by 0.6815. This will give you the diameter of you greenware spoon.

This is assuming an average shrinkage of 12%.
If you clay shrinks 13% then you would need to devide by 0.87 x 0.87 x 0.87 or 0.6585.
If you clay shrinks 15%, then you would devide by 0.85 x 0.85 x 0.85 or 0.6141.

This is because the volume reflects the cubed value of the shrinkage .....(4/3 pi r cubed).

Everyone got it?


#104543 Community Challenge #5

Posted by jrgpots on 31 March 2016 - 10:47 PM

Attached File  ceda rbreaks-2.jpg   165.58KB   0 downloads


This is my final entry.  Unfortunately it cracked to pieces... :huh: Next time I need to compress the tiles more.   The good news is that all of the glazes I made by hand.  The green matte did not show as many streak marks in testing as on the tiles.  But, I really like the texture of the tree... :)



#104401 Wood Ash Proportion As An Addition To An Existing Glaze

Posted by jrgpots on 29 March 2016 - 01:42 PM

When your ash is still wet, make pellets by compressingsome of the ash in a straw, then allow the pellets to dry.  Once dried put the pellets in a catch basin in the kiln during a glaze firing.  This should give you a good idea of what the ash will do (especially color) before adding to a glaze.



#102238 Community Challenge #5

Posted by jrgpots on 18 February 2016 - 08:29 PM

I just finished carving the relief of the mountains.  The tree branch has Barnard"s slip.  I need to do sgraffito work on the tree branch.  I have one more day of work before I let them dry, then bisque firing.



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#102043 Kiln Conversion Updraft Downdraft Chimney?

Posted by jrgpots on 15 February 2016 - 11:16 PM

This is my poor man's power burner.

I bought a 3" turbo fan from an Auto parts dealer for $29.00. It is a dc 12 volt blower that produces 145 cf/min.
I attached an old 12volt DC adapter.
I fashioned it to 3" black pvc pipe.
I fitted a cd disc to act as a damper to the airflow.
I fitted a 3" to 2" reducer on the burner side of the fan.
I fitter a sheet metal tube to the T piece.

The burner nozzle is drilled to 3/32 and the burner is easily adjusted from 1psi to 5psi. The airflow damper places the burner easily into reduction.


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#101800 What Is The Difference Between Plaster Of Paris And Pottery Plaster?

Posted by jrgpots on 11 February 2016 - 01:03 AM

My damp box is made from normal plaster of Paris. my base of by damp box is 15 x 26 and the slab is 2 inches thick.

No problems so far.


#101401 Community Challenge #5

Posted by jrgpots on 04 February 2016 - 06:41 PM

This is my initial design for the mural.  Each tile will be 7'' x 10'' when wet.  The picture is one I took of a 1,00 year-old bristle cone  pine overlooking  Cedar Breaks Monument, Utah.



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#101312 Community Challenge #5

Posted by jrgpots on 03 February 2016 - 12:57 AM

About a month ago I found Natalie Blake's site. She also has some great youtube videos of tile mural production. I will try something like this.



#100406 Cooking Pizza In A Pottery Kiln, Toxicity ?

Posted by jrgpots on 22 January 2016 - 11:02 AM

I actually think everything would be fine, especially if you wash it down with some Flint, Michigan tap water.

If you use Flint water in your glazes, they come out brighter and more beautiful. See, there is always a silver lining even to rain clouds... No wait, that would be another toxic heavy metal contaminant. It makes me want to shield myself from all this stuff....No wait. That would be made out of more lead. I'm so confused, I'm going to take a bath...No wait.Ugh!


#100298 Cooking Pizza In A Pottery Kiln, Toxicity ?

Posted by jrgpots on 20 January 2016 - 10:03 PM

Fire to cone 10, then use the ash in a new pizza glaze. It has fewer calories.