What if an air pocket gets trapped in your clay and you don’t know it? Will the kiln get damaged? Will the pottery crack or break? These are important questions
If there is an air pocket that goes into the kiln, your piece could crack, break, or even explode. This would depend greatly on if any moisture is still inside of the air bubble, but your kiln should not get damaged. Kilns are made to withstand pottery exploding. Cracks, breaks, and blowups are part of the craft. When moisture is still in your clay when firing, the chance of damaging your pottery goes way up. If fired slow enough, any moisture has a better chance of escaping, and the possibility of damage goes way down.
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Avoiding Air Pockets Altogether
When clay is mixed or recycled, air pockets get trapped in the clay. Wedging is the best way to eliminate them. Wedging is the most important step before playing with your clay. There are more benefits to wedging clay than just getting rid of air pockets. Wedging also makes the clay more maluable (workable) and gives you consistent moisture throughout the clay.
When you wedge the first few times, you may end up folding air into the clay. Folding air into your clay may happen until you get the hang of it and find your favorite method. The more you wedge, the easier it will get.
Different Methods Of Wedging Clay
There are several different methods of wedging or kneading. If you see the term kneading the clay, don’t get confused. It is also called kneading as in kneading bread. The concepts are the same. Getting the clay ready to handbuild or throw on the wheel.
There are 4 different methods of wedging your clay by hand. The Ram’s Head, Stack and Slam, Spiral, And Wheel wedging. For more detailed information check out How To Wedge Clay With A Step By Step Video.
Using a Pugmill, which is also known as a pugger would be the ideal way to wedge. Pugmills are awesome. They wedge clay automatically.
They are great for recycling clay or even running it through just before Throwing or Handbuilding to make the clay more pliable and even out the moisture. A Pugmill can thoroughly mix your clay in just a few minutes.
When you are starting out a Pugmill is not one of the first pieces of equipment on your list to purchase. Buying pre-pugged bags of clay is the way to go for beginners.
Even when you have a fresh bag of clay, you will still have to wedge it. The clay has been sitting for a while during shipping, and the moisture consistency is no longer the same throughout the bag.
Stack and Slam Wedging
Also called Cut and Slap Wire Wedging. This method is my favorite plus it’s the easiest for beginners. This method also compresses your clay which in turn helps to prevent cracking.
Take your wire and cut your clay in half, turn the clay in your hand on an angle and slap it down on the piece of clay on your table, then continue to slap it down 3 or 4 times turning the clay to compress it together.
You can also cut the clay several times and stack it then slam it down on the table several more times to compress it. You will want to do this at least 20 to 30 times.
When you’re done slapping your clay around it will be in a square or rectangular shape. You will want to slap the corners down to form it into a ball, so the moisture content stays even throughout the clay. Then you can start playing with your clay.
Coning your Clay
Also called Towering. Coning or Towering is wedging on the throwing wheel.
Slap your clay on the wheel and bring it up to a tall tower shape then flatten it down into a beehive shape.
Do this two or three times. You don’t want to cone the clay too many times because you’re using water with this technique and it can soften your clay too much. Coning also helps with centering your clay.
Ram’s Head Wedging
Rams Head Wedging seems to be the most popular. When done right it is most effective. The key is not to fold the clay. That motion creates bubbles.
You want to bring the clay up towards you and press down and away from you keeping your fingers on the side and your thumbs on the top, so the clay doesn’t come out the sides.
Beginners tend to push down too hard, and the ram’s head looks like it was run over by a bulldozer.
Also known as Shell Wedging is another method you may want to try. The spiral method is more advanced and a little trickier to learn, but done in the right way this method mixes the clay and eliminates the air bubbles very effectively.
Tip the lump of clay to your left and push with your right palm. Turn your clay about 15 degrees and do it again. If you are doing it correctly, your clay will have a spiral shape that looks like a shell.
For more detailed information on the different wedging techniques check out How To Wedge Clay.
You will need a good surface to work on if you are wedging at home. The most common surfaces are plaster covered in canvas, wood covered in canvas, masonite, concrete, or granite.
Poke Holes in Hollow Pottery
You should poke a hole in your hollow pottery. This helps the inside of the piece to dry more evenly to prevent cracking. Make sure your hole is large enough so when the clay shrinks as it drys the hole will still be big enough to allow any moisture to escape.
Find a cleaver spot to poke your hole. If you make a bunny or pig, you could poke the holes in his ears or nose.
Pottery should be Bone Dry Before Firing
You want to make sure the clay is bone dry before putting it in the kiln. The general rule is to put the piece against your cheek, and if the clay is cold, it still has moisture in it. If you are drying your pottery outside, make sure you don’t put it in the sun. That causes uneven drying that may result in a crack or break when you put it in the kiln.
The thickness of your pottery also matters. As a general rule, it’s best not to make your pottery more than an inch thick. If your piece is too thick, there is a higher chance of having moisture and air pockets trapped in your pottery.
Therefore, the chance of breakage in the kiln is more likely. Thinner pottery has less chance of getting air pockets, dries faster and more evenly.
Drying Your Clay Properly
If you have made a piece of pottery that’s hollow and totally enclosed and didn’t allow the pot to dry properly, the moisture will turn into steam and get trapped in the air pocket.
When the outside of the clay piece is dry, it shrinks a bit, and if the inside has moisture in it and the clay expands it puts pressure on the outside walls. The pressure of the steam will build, and the pot will crack, break, or even explode.
If children or guests are present warning signs should be posted in the kiln area because of the potential danger. The kiln can get hot enough to burn your skin when heated.
For more detailed information check out Are Pottery Kilns Safe?
Slow Fire Your Pottery
Firing your kiln at a slower rate is important. If your firing rate is too fast, your pottery will crack or break. Firing at a rate of slow to medium is good. Keep in mind a slower rate of speed is recommended. This stops the build-up of pressure from heat and allows the gases and any moisture to escape safely.
Candling is when you place your pottery in the kiln at a low temperature before the first firing. You may want to candle your pieces before firing.
Depending on your kiln Candling can be done manually by turning the bottom burner too low and leaving it there for 8 or 9 hours. If you have an electronic kiln, you can program it to stay at 180 degrees for 8 to 9 hours. This method seems to eliminate all breakage.
POTTERY CRAFTERS THOUGHTS…There is a saying in pottery. Never fall in love with the piece until it leaves the kiln for the last time. Yeah Right!