“Thereafter beginning from the left he poured drinks for the other
gods, dipping up from the mixing bowl the sweet nectar.
But among the blessed immortals uncontrollable laughter
went up as they saw Hephaistos bustling about the palace.
Thus thereafter the whole day long until the sun went under
they feasted, nor was anyone’s hunger denied a fair portion,
nor denied the beautifully wrought lyre in the hands of Apollo,
nor the antiphonal sweet sound of the Muses singing. ”

– The Iliad, By Homer, Book 1 

 

 

The Mixing Bowl

 

One of the most useful pottery forms (besides common mugs or soup bowls) are mixing bowls. Mixing bowls are diverse and can be used in many ways. A large bowl makes a great centerpiece, like on a kitchen counter or dining table with fruit inside. Large mixing bowls are also useful for baking and mixing recipes, raising bread dough, or soaking beans.

 

 

To make a mixing bowl, I start with 8 to 10 lbs. of clay. I knead the clay to get the air pockets out and mold into a cone shape. This makes it easier to center on the wheel. In the past, I have also added smaller lumps of kneaded clay on top of each other to make the cone while it’s on the wheel head.

I then place the large cone on the wheel head and turn the wheel by hand, slapping the cone while rotating the wheel to center it. I stand to throw and have my wheel up on blocks. This helps me prevent back injuries from being hunched over. 

 

Throwing the Bowl

 

When the lump of clay is centered on the wheel, I cone it up and down a few times to center the clay throughout the whole lump. I then flatten the cone on the top, pushing down to compress the clay. Now it is time to open the clay.

I roll my thumbs in and push down until I have about a 1/2-inch base. I pull the clay out, creating the floor. I still leave the clay narrow (like making a vase) and pull up for height before pulling out. At this point, it is important to compress the sides and rim after each pull up. 

 

 

Once the height is achieved, I pull out the sides and create the bowl shape the way I like. Sometimes I use a small mirror on the other side to see the shape from the back. Once the shape is how I want it, I then compress the sides and top some. I take a rib and compress and shape the inside, removing any ridges or grooves that could catch a spoon. For this, I use a large throwing rib or a plastic pizza cutter.

 

Now the inside is compressed and shaped, I cut the top rim with the pin tool to even it out. I then compress the rim and thin it to prepare it to be rolled. I carefully roll the rim over and compress the underside. A rolled rim seems to strengthen the bowl, which helps it keep shape during drying and kiln firings. I cut the bowl off the throwing bat with the wire tool and let it stiffen up.

 

Drying and Trimming

 

Once the bowl is stiff enough to handle being flipped, I turn it upside down and expose the bottom to air. It is important to let the bottoms dry first. Once it’s leather hard, I trim the bowl and make sure it has even thickness in both the sides and bottom. Even thickness prevents cracking from uneven drying. 

 

It is possible to speed dry if bottoms are put to heat to dry first. Some set their large bowls upside down in the sun, upright on a kiln lid, or set on metal shelving over a wood stove to heat the bottoms and dry all the way through.

 

When the bowls are bone dry, they can be loaded into the bisque kiln. Center and top shelves are good for bowls, as they need more even heating. If using a gas kiln, they need to be protected from the direct flame and the kiln needs to be heated slowly until just after red heat. Once the kiln reaches bisque temperature, the bowls should cool slowly to prevent cracking from thermal shock. Now the large bowl is ready to glaze.

 

Glazing the Bowl

 

I blow into the large bowl to remove any dust, then fill the bowl to the rim with glaze from a 5-gallon pail after stirring it well with a paint mixer attachment on a drill. Then I dump it out. Depending on the glaze’s gravity, it may need to be done twice if thin. I let the bowl dry completely.

 

To glaze the outside of the bowl, I dump glaze into a large tub, then hold the bowl upside down and at a slight angle. I dunk the bowl and then turn it straight to create an even glaze line about a 3/4 inch up from the bottom. I pull the bowl out and let it dry. Wait for the drips to stop before carefully turning it upright. 

 


 


Firing The Bowls

Once dry, the bowl is ready to fire. I make sure no glaze is on the bottom and even up the lines if I need to. I load the bowls in the kiln. For my kiln, a gas firing takes about 6 hours to reach cone 6 or 2223F. The kiln then cools for 24 hours before it is opened and unloaded.


After being unloaded, I check the bowls for cracks. I then wash them out and send them off to their new homes, post them online, or take them to area shops for sale.

 

I do hope you enjoyed this little post on how bowls are made!   Have you tried to make large bowls?  How would you use a large mixing bowl?  Let us know in the comments!

Written By,
Alford Wayman
Artist/Owner
Creek Road Pottery LLC

Edited by:
Erika Sickler
Content Writer/ Editor
Creek Road Pottery LLC

If you enjoyed this post and are a lover of pottery, sign up for our newsletter and become a raging fan.

 

20160822

Carbon coring or “black coring” can be an issue when firing clay bodies. While doing some experiments with reduction firings I had many pots that were cracking in the process and had no idea why. It seemed that the cracks were from fast cooling, as they were clean breaks through the glaze with sharp edges. Little did I know that this cracking was caused by carbon coring or “black coring”. I did some comparisons wth cross sections of the broken pots and noticed that this discoloration did not happen in my oxidation firings but only in reduction. I dug out my ceramic books and searched online to find out what this issue might be.

Shattered By Black Coring

While researching I found a post by the Lugna Clay company entitled ” Bloating and Black Coring”, which seem to suggest that I may need to bisque fire my clay body properly.  The theory behind the article suggested that not all the carbon was burned out of the clay body and the kiln also may need to be vented better in the bisque firing. The clay body I was using was AMACO high-fire warm brown 58-M stoneware clay. I only had issues with bloating when I accidently overfire it a few times on the bottom shelves while trying to reach cone 6 in the middle of the kiln.  The clay body was high in iron content which, I later found, created the issue with black coring when I reduced the updraft kiln to produce a body reduction. The iron in the clay and the reduction process was a bad combination and would produce a bad kiln load of pots.  Bowls shattered as they cooled.

Black Coring – The Cause

The answer to the problem came from an excellent research report entitled “Calcium and sulphur distribution in red clay brick in the presence of a black reduction core using micro X-ray fluorescence mapping”. by L.Gredmaier, C.J.Banks , and R.B. Pearce. These findings can be found on page 2 and 3 of this report:

“The following factors determine the extent of black reduction coring in red clay ware:

- Firing time – a longer ring time can eliminate the black reduction core.

- The oxygen atmosphere during ring. Lack of oxygen promotes the formation of black reduction cores.

- Iron oxide content in the raw clay.

- Carbon content and burnout or oxidation of carbon during firing of the raw clay.”

The research in this report stated also that the red iron oxide was converting to magnetite.

To the potter, according to “The Potter’s Dictionary of Materials & Techniques” by Frank and Janet Hamer, on page 26,  means this conversion created weakness to the clay body caused the clay to vitrify at a lower temperature due to the red iron oxide and carbon converting to black iron oxide and carbon dioxide, which creates an active flux . The pots become brittle and fragile.  One mug I took from this load popped apart while I poured coffee in it as a test, sending shards across the table, because it could not withstand the thermal shock due to black coring.

Black Coring – The Solution

The solutions to black coring from the article link to above would be to use a clay body with less iron content.  Also, it is suggested that bisque firings should be slower and to the correct temperature to allow carbon burn out.  I personally found that in my high iron clay body, if I skipped the body reduction of the firing and reduced the kiln towards the end of the firing, I still got reduction glazes to look great without black coring.

If any of you who read this have found this helpful or have your own findings, feel free to leave a comment!

 

 

20160512_185726
Al Wayman
Artist /Owner
Creek Road Pottery LLC