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Since the mid-1970s, ceramic artist Peter King has been combining his experience in the building industry with his love for clay to make architectural works of art. Many of his projects involve columns like those shown to the left so Peter had to come up with a really great system for making tall, straight-walled cylindrical pieces.

 

The best way Peter has found to do this is by wrapping slabs around cylindrical forms made of plywood and roofing flashing. Today, he explains this method, which allows him to make columns in virtually any height or diameter. Take it away, Peter! – Jennifer Harnetty, editor.

 

fig.1

fig.1

Throughout my career, I’ve used a construction system based on wrapping slabs around tubes of varying heights and diameters to create architectural works of art. This method proved to be a much easier way to build a tall, straight-walled piece rather than using the conventional method of coil or slab construction. With this technique, it’s easier to make cylindrical forms rather than throwing them on a wheel.

 

Flashback
My desire was to create lightweight tube forms that I could make in any desired height or diameter. I resolved this using my construction background. I remembered that roof flashing came in various thicknesses and widths and was readily available at home centers. Flashing is the thin metal commonly used to seal and waterproof junctures in a roof. Made of aluminum or galvanized steel, it’s relatively easy to cut and bend. It’s sold in a roll, and so it has a spring-like memory, making it difficult to lay flat. The tube forms I make take advantage of this memory.

 

fig 2.

fig 2.

Good Form
To make a custom tube form, begin by determining the finished outside diameter of the fired ceramic work. Then add the shrinkage of the clay (wet to fired percentage). From this diameter, deduct the thickness of the slab. This calculation gives the outside diameter of the form you need to build.

Begin building the metal tube form by making two doughnuts from ¾-inch plywood equal to the outside diameter. The doughnut holes create handholds for manipulating the form.

Once these plywood forms are cut and the edges sanded, unleash the coiled metal flashing. Caution: Flashing has sharp edges and corners, so take extra care when cutting the banding. Once cut, it will spring open abruptly as it releases bound up energy from being so tightly wound. 

fig 3.

fig 3.

Measure the outside circumference of the plywood doughnuts using a seamstress tape (figure 1) and add two inches to create an overlap at the seam when you roll the flashing around the forms. Cut the flashing to length using metal shears. 

Position the plywood doughnuts with their outside edge flush with the outer edge of the metal flashing. Holding the plywood forms at right angles to the metal flashing, begin fastening it to the plywood with short nails or screws (figure 2). Use 1¼-inch #6 coarse thread screws for this purpose. Tip: When using screws, pre-drill holes every two inches along the edge of the plywood.

Measure the inside distance between the two disks and cut a 1- to 1¼-inch square post to length so that it fits snugly between them. Insert this and place it tightly against the inside of the metal tube so it spans the outside edge of the metal seam. Fasten this post into each plywood disk. Secure the lapped flashing to the post. 

fig 4.

fig 4.

Forming the Clay Tube
Roll out a slab for the base of the form the same thickness as the slab you’ll make for the cylinder. I prefer at least one inch-thick walls. When rolling out the slab, make it four to five inches larger than the outside diameter of the clay cylinder. Lay this base slab on a wheel and cut roughly to the width of the wheelhead or bat.

Set the metal tube form on the slab. Center it and mark a groove right against the tube. Mark another groove on the base slab at the outside diameter of the clay cylinder. Score the area between the lines and coat it with a thin slip (figure 3).

Roll out the slab for your cylinder onto a piece of canvas, making sure that this slab is a few inches longer than the outside circumference. The extra length allows you to lap the slab onto itself when you roll it on the tube.

fig 5.

fig 5.

Pass the clay through the slab roller, making it wider than the finished width of the slab you need for the height of your cylinder. Leave the slab affixed to the canvas, as you’ll need it to support and steady the slab as you pull it around the metal tube. Roll up the top side of the canvas. This will become your handle for pulling the slab around the metal tube (see figure 9). Square off the edge of this slab next to this rolled up canvas and cut the two sides parallel to one another.

Coat the metal tube with vegetable shortening: this makes it possible to tilt the rolled and secured slab vertically without it falling off the tube, and also acts as a release agent once the slab is properly positioned. On smaller diameter tubes, a paper interface will be sufficient.

Once the slab is cut into a rectangle, place the metal tube on the pre-cut edge of the slab. Position the tube so that the wooden post of the tube is at the bottom. This gives an inside handle while the rolled up canvas forms the outside handle. Grab the rolled up canvas, lift and pull the attached slab onto the metal tube in a continuous rolling action (figure 4). While rolling the slab around the tube, take care to keep the two aligned. Once you have wrapped the slab onto itself thoroughly, cut away any excess, leaving a two-inch lap at the seam. Slip and score the surfaces and press the seam together . Roll the tube onto this seam to compress them.

Lift and tilt the cylinder and tube onto the base slab. Try to land the cylinder using your center grooves as a guide. If you miss slightly, immediately slide the cylinder to the center using the slip as lubrication and your previously drawn circumference lines as a guide.

Live Large!
Turn to Slab Techniques to learn how to amp up the scale of your ceramic art!

 

fig 6.

fig 6.

Joining the Parts
Once centered, begin working the base slab against the metal tube using a rubber or metal flexible rib (figure 5). Go around the cylinder, pushing the clay against the tube in a series of firm upward vertical passes. Next, use your fingers or a toothed scraper to work the lap joint seam both horizontally and diagonally, so you’re moving clay from the top slab to the one below and reducing the thickness of the overlapped seam. If the cylinder is to be wheel-thrown later to add throwing lines or texture, great care should be taken to compress and smooth this seam to the exact same thickness as the rest of the slab wall.

Tip: All of this pressing and compression may cause the slab to stick to the metal tube, making it difficult to remove. I always separate the clay from the metal tube after the initial vertical compression passes. Using the hand hole in the top doughnut, pull the metal tube up a few inches, turn it slightly, then gently slide it back into the cylinder until it rests back down onto the base slab (figure 6). Once the metal tube is separated from the clay cylinder, it is easy to remove even after full compression.

fig 7.

fig 7.

At this point, I throw the base of the cylinder, joining the base slab to the cylinder. Now that the cylinder slab is in place and smoothed to the metal tube, the base slab can be cut to the right diameter. Wet the wheel head and band of clay, then with a flexible rib or wooden knife, lift the band of clay from the wheel head and fold it up onto the clay cylinder (figure 7). Spin the wheel at a low speed and use a needle tool to cut a 1 1/2 to 2-inch tall band around the cylinder. This forms a strong bond between the base slab and the cylinder wall. This folded clay can then be finished to your style or taste.

Once the base and cylinder wall are joined, remove the tube from the inside before finishing the rim, then re-center the top of the cylinder by tilting it accordingly while slowly turning the wheel and checking center with a steady index finger. Once the top is centered, cut off the upper edge of the cylinder to level the top in preparation for throwing the upper cylinder.

fig 8.

fig 8.

Begin by spinning the wheel at the same speed you’d use for finishing a large wheel-thrown pot. Use one hand to stabilize and support the cylinder wall, and the thumb and index fingers of your other hand to fatten, compress, and round the upper rim, stabilizing the cylinder for further throwing. Depending on my objective, I can then treat the cylinder in various ways (figure 8).

Double Cylinder Columns 
I create structural columns in 4-foot sections. Since this is a difficult size to manage in a single cylinder, I resort to the old inverted stacking technique used to create tall work from conventionally wheel-thrown cylinders. To achieve this using slab and tube construction, I simply forego the aforementioned throwing of the upper rim. In this case, I leave the cylinder wall perfectly straight and vertical; I do cut off the upper edge of the rim while spinning the cylinder on the wheel. This leaves a leveled rim, allowing me to join the two cylinders together.

When stacking two cylinders together rim to rim, I take a caliper measurement of the outside diameter of each cylinder, although this is usually redundant since the two cylinders are rolled around the same metal tube.

After making the individual cylinders, I let them stiffen for a day or two. In dry weather I cover just the top edge of the cylinder to keep it slightly softer. This facilitates the joining of the two column sections. After these cylinders have stiffened for a day or two, I invert one onto the other to form a closed ceramic column section. Once sewn together, the seam can be erased by smoothing and or texturing the entire surface.

fig 9.

fig 9.

Installing Columns
As I have mentioned before, stoneware has immense comprehensive strength, so for most construction purposes these cylinders do not require infilling or other reinforcments. Note: Check with your builder or a structural engineer to be sure this is true for your specific situation. For most installations one need only to perforate each end of the column with a few 1-inch diameter holes. Upon installation place a pile of premium polymer thinset or medium bed mortar on top of the piece to be set, then stack and level the next column section on top of the lower section. The mortar will ooze into the holes. Once set, this mortar will form cement pegs as strong as or stronger than the surrounding stoneware. 

During Hurricane Ivan we had a house lose its roof but the ceramic columns set with this method remained completely intact and undamaged.

To learn more about Peter King and his architectural ceramics workshops and books visit www.peterkingceramics.com.

 

 

 

 

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