Thursday, July 31, 2014


A fellow potter told me once that they hated trimming.  They found it tedious.  I LOVE trimming.  I suppose throwing is a bit more dynamic, but I have a perfectionist streak, so trimming is one of my favorite things.  I find it very meditative, and the state of the clay at that point of the process is delicious.

When clay is ready to be trimmed, it still has the rich, moist color of wet clay, but it is firm enough that curls of clay cut away smoothly, without stickiness.  Something like cheddar cheese, or fudge.  I use a dark claybody, rich with iron oxide, so the trimming stage feels like working with chocolate.  

During the year that I had studio space at Feet of Clay, in Brookline, my workspace was right in their front plate glass window, among the pots of geraniums.  Pots I threw in the morning would soak up the sun and be ready for trimming after lunch.  Now, I work in a damp, cool basement, so it usually takes a few days for pots to dry enough to be trimmed.  A day after throwing, the rims of small cereal bowls are firm enough that I can cut the pots off of their bats to finish drying upside down.

Any pot that is meant to have a trimmed foot is thrown with a bit of extra thickness at the bottom that will eventually become the foot.  That extra thickness dries slower than the thinner rim and sides, so flipping the pot upside down as it dries exposes that wet bottom to the air and helps even out the drying process.  It also helps keep the rims from warping.  After a day in the stranded-turtle position, cereal bowls are ready for a trim.  

First step.  Very important!  Look shape of the inside of the bowl.  Is the bottom flat?  Curved?  What is the shape of the curve?  Half-circle? Parabola?  Is there any extra fat in the walls near the base that should be removed?  On a well-trimmed pot, the shape of the outside matches the shape of the inside, so that the walls are the same thickness all over, and the bottom is the same thickness all over.  The foot ring is the only part that sticks out, and it is the same thickness again.  This makes for a harmonious look, a piece of pottery that feels light, instead of clunky, and will make it much more likely to survive the stresses of final drying and firing without the dreaded s-crack.  Clay shrinks as it dries, and then again during the bisque and the glaze firing.  Thinner areas dry faster than thicker areas, so they shrink first, and the different shrinkage rates crack the clay.  If you manage to make it to the firing, thinner areas heat and cool faster than thicker areas, which again, makes them shrink at a different rates, and again, causes cracks right down the center of the pot.

You also want to keep in mind your final glazing at this point in the process.  If you are going to need to hold this pot upside-down by the foot to dip the rim in glaze when it's all done, you are going to need to plan out a foot ring that is tall enough for your fingers to get a good grip.

So take a good long look a the inside of your pot in comparison with the outside and plan whither thou shalt whittle.  You can make a quick mark with your thumbnail on the bottom of the pot of where the foot ring will sit.  You can make a mark on the side of a spot where you need to trim a bit of excess weight.

The bowl is placed upside down on the wheel.  The wheel head has a series of concentric rings scribed into it that help me get the bowl back roughly on center.  With the wheel spinning very slowly and my hands in a well-supported position, so I don't accidentally jiggle, I hold a needle tool against the side of the pot where the foot will be.  As the wheel spins, the tool draws a dash on the side of the pot if it isn't entirely centered.  The longer the dash, the closer to on center the pot is.  I stop the wheel and move the bowl a squidge, then try again.  When the tool draws a light circle all the way around the pot, I know I'm back on center.  I roll out three quick coils of clay about an inch long and thick as my thumb and squash them onto the wheel head so that they hold the bowl steady for me.  There is also a tool called the Giffin Grip that you can use to get your pot re-centered and immobilized, or you can use the "tap centering" technique, but I'm pretty speedy doing it this way, so that's what I do.

And then I trim.  I like the small, cheap Kemper trim tools that come with beginner pottery tool sets, but find what works for you.  Dolan tools have the advantage of being re-sharpenable, so you only have to buy them once, but then you have to be confident in your ability to sharpen them, and they are an expensive initial investment.  There are Asian-style tools that look like the knives used to turn wood on a lathe.  There are giant loop tools that let you confidently carve off great swathes of clay if you're a confident hacker roughing in the general shape on a giant bowl before getting more detailed, or want a rough, hacked look as a stylistic choice on your finished product.  I like the precision of the little Kemper double-ended loop tools.  One lasts me about 2 months before it's too dull and I throw it away. About once every six months I empty the tiny waste basket in the studio and it contains 3 loop tools and  the melty cone packs from six months of firings.  Six months of studio trash fits in a shoe-box.  It's pretty cool.

Just like when you throw, when you trim you need to hold your hands in a supported position.  Elbows tucked against your body, or propped on your knees.  One hand supporting the other, so that you can make tiny, slow, adjustments to your hands without being thrown off by the force of the clay pressing back at you as the wheel turns.  With the wheel running at a medium speed, mark the inside and outside of where the foot ring will go.  Then find the angle to hold the trim tool to the pot so that it carves off a smooth, thin strip of clay.  If you're someone who likes to peel an apple in one smooth, unbroken motion, you'll love this.  Remembering what the inside of the bowl looked like, peel away excess clay, so that the foot ring is roughed in, and then slowly refined.

Beginning potters tend to be so worried about accidentally trimming all the way through the bottom of the pot that they actually don't trim enough.  People can spend years pecking away hesitantly. My best advice is go big or go home.  The only way to know how much is too much is to go ahead and trim right through a few pots.  Trim through ten pots right at the beginning and you'll save yourself years of timidity and clunky thick pottery.  As you trim, stop the wheel periodically, and give the bottom of the bowl a light tap with a finger, like thumping a drumhead.  Listen to the quality of the sound it makes.  With practice, you'll start to recognize the sound that says you're about to trim through the bottom, and the sound for "just right."  Some potters like to push gently on the bottom of the pot.  With experience, they can tell what amount of give to the surface means they are just right.

The foot of a pot is one of it's more distinguishing features.  The "terminations" (rims and feet) are a big part of a potter's particular style.  Take the time to make nice, crisp, definite ones.  There's nothing sadder to me than a nice pot with a cruddy little foot.  If it's straight up and down, make it really straight up and down.  If it curves out, make it a clean, defined curve.  If it curves in, make it a clean inward curve.  Foot rings often have multiple curves and angles to them.  You may need more than one tool to get the profile that you want, and your tools need to be sharp and clean to do the finishing touches.  Foot rings can echo, in miniature, the larger profile of the pot.  Or reverse it.  Or contrast from it.  A short, minimalist ring is hidden in the shadow of the finished piece, lending simplicity to its form.  An extra-tall complex foot becomes the focal point of the piece.

Trimming roughs up the smooth surface of the clay.  The more surface area of a finished pot touches the table, the more chance that some little grit in the clay scratches the table.  If you want the look of a wide foot ring, consider angling it ever so slightly off of the horizontal, so that only its inner or outer-most edge will actually touch the table.  You can also use a shammy to smooth a foot ring the same way you use it to smooth a rim.  I like to use a flexible metal rib to smooth the grain of the clay back down on the side of the pot and inside the foot ring after trimming.  

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