Traveling in Style Sumi von Dassow

Appears in the Sep/Oct 2016 issue of Pottery Making Illustrated.

Lately I’ve been trying to avoid putting food in plastic containers. Sure,  some plastics are BPA-free these days, but what other nasty chemicals might be in plastic? Fortunately, as a potter, I can make myself all sorts of ware that I feel confident is safe to use. One of those things that is so often made of plastic is the travel mug. I don’t want to fill a plastic container with a hot acidic liquid and let it sit for hours. Even if you find a stainless steel or ceramic car cup, the lid is usually plastic. So, I gave myself an assignment; design a ceramic car cup with a ceramic lid that won’t fall off as I drive or carry it out to the car.

First of all, I had to figure out how big a car’s cup holder is. Fortunately the industry has agreed upon a standard size of 7 cm across the base of the cup holder, and generally 6 cm deep. The auto industry is global, and most of the world uses the metric system so for this project it’s much easier to measure in centimeters than inches. The width at the base is the maximum diameter I can make the foot of my car cup, and the depth tells me how high I must put the handle. Allowing about 8 cm for the length of my handle, if my handle must end 6 cm above the foot, I have to make the cup at least 14 cm tall and preferably taller. Adjusting for 12% shrinkage, I make the foot of my car cups 8 cm across, and I aim to make them 16 cm or more in height, with the bottom handle attachment point no lower than 7 cm.

Throwing the Tall Cup

To make a mug with a locking ceramic lid, start out with a 2-pound lump of clay. Set a pair of calipers at 8 cm to measure the foot, and put a piece of tape at the 16 cm mark on a ruler for the height. Center the lump of clay, and open it up leaving the floor only inch thick. Note: You don’t need a foot on a car cup, so there’s no reason to leave extra clay at the bottom. If you make the bottom about the diameter of a standard yellow throwing sponge (2 in. (6 cm)), that will be about right.

Now pull the clay up into a tall narrow cylinder, leaving the rim extra thick so you can make a gallery for the lid (1). Ideally you want your calipers to just fit around the mug at the base—if you don’t pull up enough clay then the calipers won’t fit around the foot and you’ll have to estimate how much clay is left to trim off. As long as the mug isn’t too wide across the inside of the foot, you’ll be fine.

Make sure the mug flares gently toward the rim and doesn’t get too much wider in the bottom 7 cm where it must fit into the cup holder. I make the rim about 9–10 cm across, meaning once I make the gallery for the lid, I won’t be able to get a hand inside it—so be sure to rib the interior before you create the gallery.

Create a Gallery

To create the gallery, use the rounded end of a wooden tool. Carefully supporting both inside and outside the rim with whatever fingers you can spare, push the tool gently into the thickened rim, pushing the extra clay down to create a ridge inside. Keep going until the ridge is depressed at least half an inch or so, up to an inch. Normally, a gallery is only inch deep, but since you have to drink out of this rim, it’s uncomfortable to have it too close to your lips.

Now you have a horizontal flange inside the rim to support the lid, and the rim should be a standard thickness. If the rim is still thick, go ahead and pull it up thinner and taller. Make sure the rim continues to flare slightly above the gallery so you don’t have a hard time getting the lid in or out. Cut off any extra clay on both the flange and the rim, and smooth both edges with a chamois. Measure across the gallery with calipers (2). I don’t cut the mug free from the bat. This way I can trim any extra clay from the bottom half once it dries a bit without having to recenter it.

Set the ruler with the tape mark next to it to make sure the rim of the mug is above the tape (3).

Throwing a Lid

Throw the lid right side up, off the hump, with the knob depressed in the center—picture a deep saucer with a knob in the middle. Center a few ounces of clay at the top of the hump, about the size of a small piece of fruit. Create a groove in the hump of clay below the centered portion and place your pinkie fingers in this groove as you open up the clay with your thumbs. Separate your thumbs as you push them down, allowing a knob-sized lump of clay to remain between them (4). You only have to go down inch or so. Shape the knob and cut off any extra so it’s not too big, then flatten the clay around the knob and pull up a short wall. Make sure the space around the knob is wide enough that you can grasp it with your fingers. Now lay down the rim, creating a horizontal edge that will rest on the gallery (5). Cut off any extra, making sure the rim fits inside your caliper measurement.

Tip: The knob shouldn’t protrude above this rim, or it will hit your nose when you drink out of the cup! Also this will make it easier to turn the lid over and trim it. Cut the lid off the hump and set it aside.

Fitting the Lid

When your mug has stiffened up a bit, trim any extra clay from the bottom half. Make sure the first set of caliper measurements comfortably fits around the foot of the mug, but still leave it attached to the bat in case you need to trim it later. When your lid is leather hard, match it up with the mug to see how it sits in the gallery. You can always trim a bit off the rim before you turn it upside down to trim the base. Center the lid upside down and trim the extra off the bottom half (6). If you can’t trim the lid enough to get it to fit down inside its gallery, put the bat with the mug back on the wheel and trim the gallery a tiny bit narrower until the lid sets down into it. (Make sure you get all the trimming scraps out of the mug!) The rim of the lid should now rest easily on the gallery.

Adding a Locking Feature

Cut two notches from the gallery of the cup rim, exactly opposite each other (7). Next, turn the lid upside down, and, using magic water or slip, attach two small balls of clay to the base of the lid, exactly opposite each other (8). Smooth the balls on and shape them into points. Test fit the lid on the mug. You want the added balls on the lid to fit exactly into the notches on the gallery, then you need to be able to turn the lid so the balls slide under the gallery and hold the lid on if you try to lift it.

Adjust the shape and position of the balls on the lid until the lid turns easily and there isn’t too much play when it’s in the locked position. The last step is to cut a notch from the rim of the lid, exactly between the clay balls (9). When the lid is on, it can be turned 90° to line up the notch in the rim with one of the notches in the gallery, allowing you to drink from the opening. When the lid is turned less than 90°, it’s locked on but the opening is covered, reducing splashing as you travel with your full mug. The lid is recessed enough to keep your nose from bumping when you drink.

Finishing and Adding a Handle

To finish the mug, attach a handle exactly between the cut-outs in the gallery. Make a mark 7 cm above the foot and attach the handle above this mark (10).

Dry the mug slowly with the lid in place. I glaze the mug rim and lid completely and fire the lid separately on stilts to avoid leaving unglazed areas that will get stained with coffee, but there’s no functional reason you couldn’t wax the gallery and the rim of the lid and fire them together. Be sure to use a food-safe liner glaze.

Sumi von Dassow is an artist, instructor, and regular contributor to Pottery Making Illustrated. She lives in Golden, Colorado. Check out Sumi’s book, In the Potter’s Kitchen, available in the Ceramic Arts Network Shop.