Saturday, December 3, 2011

Large Cottonwood Bowl

One of the concepts on which I've been working for many years was to fabricate a large, shallow slab bowl impressed with large leaves, the lip of which was cut to the edge of the leaves.  I wanted to use the basin from a large cement birdbath I had been given by my friend Catherine Dumke from her Mother, Dorothy's, house, a vessel I had used to make a series of large birdbaths with stands back in 2008.

I started out using large Redbud (Cercis canadensis) leaves.  The process I used initially involved rolling out a rather thick slab of clay.  I applied the leaves in a pattern large enough to fill the basin - lapping four leaves, tips toward the center, four-square in the center, then surrounding them with another eight leaves, aligned so they carried on the axes determined by the first four leaves, with four additional leaves to fill the interstices.   I cut out the entire piece using a very sharp tool and pulled away the excess clay.  In order to support as much of the slab as possible to minimize stresses, I carefully rolled the slab onto my large pottery rolling pin, which I then kept from rolling while bringing it over to lay into the mold.  Once centered in the mold, I pressed it in with the relatively flat side of a smooth river stone to get as true a form as possible.  Then I'd let it dry.

Of course, being the rather impatient person I am (no snide comments, please), I would dry the piece as quickly as possible - but it would still take a couple or three days.  I would inevitably end up with stress cracks at the margin of the piece at the centers of some of the leaves and where the leaves met and overlapped, points where the clay experienced the most stress from the fabrication and drying processes.

Large Cottonwood Leaf Bowl
I can't tell you how many of these pieces I tried to make.  At least two early this year, with the same result.  (Let's talk about the definition of insanity, shall we?)  Tackling it once more this fall, I followed the same process and tried applying small medallions of clay with stamped impressions at each stress point.  This was a bit better structurally but I wasn't pleased with the result - not as "clean" as I really wanted.  Then I backed off, using some large Eastern Cottonwood (Populus deltoides) leaves for a smaller piece.  I used the same technique, but the piece buckled and puckered - it was pretty interesting looking and I stayed with it, but it wasn't what I was really looking for.

Tiny, Small, Medium and Large Cottonwood Leaf Bowls
Taking a break from this design concept, I started working with some Eastern Cottonwood (Populus deltoides) I gathered near my house, returning to a design I first developed with Redbud leaves, in which the leaves' bases overlap in the center of the bowl with the tips tapering to the outside.  I had done pieces with large leaves before, but decided to make a set of four graduated pieces, reflecting the four bowl sizes I had found in my Sasaki Colorstone stoneware.  Because of how I was orienting the leaves, I could roll out the clay slab (thinner slabs for smaller pieces), smooth the surface, apply the leaves and roll them into the clay, cut them out and then press them into the bowls with ease - because the leaves tapered to the outside, so they fit into the bowled forms with no puckering or buckling.

Tiny, Small and Medium Cottonwood Leaf Bowls
This approach wasn't going to work when I returned to pieces with the leaves pointing inward - I already knew the clay would buckle and pucker if I rolled the leaves into the clay first and then tried to fit the slab into the mold, resulting in pieces that looked cruder than I wished.  A new approach was clearly in order for these designs.  So I rolled out slabs of clay (again, thinner slabs for smaller pieces), formed them into each of the bowls using a sponge and soft kidney, then applied five leaves of relative size into each piece, with the leaves pointing in.  After I had placed the leaves where I wanted them, I used the river stone to press the leaves into the clay and then cut them out with the sharp tool.  All of these pieces seemed to come through the drying process pretty well.

I tried another very large bowl using unusually large Eastern Cottonwood leaves I had collected from saplings at my friend Chris Hopp's workshop in Dewitt, Michigan.  This time, I decided to roll out the slab, cut out a large piece, form it into the mold, smoothing it completely by alternating with a soft rubber kidney and a natural sponge.  Then I applied the twelve rehydrated Cottonwood leaves in the same pattern I had used before, using the flat side of the river stone to get the best impression possible.  (This actually works quite well in pressing the leaves in - there is no need to use an edge of the stone to press in the leaves; the flattish side of a river stone, swept over the surface with some consistent pressure, works just fine, maintaining a very consistent overall plane in the piece; if it starts to stick to the leaves, just spray with a little water.)  Then, using the sharp tool, I cut the margin to the edges of the overlapping leaves.  I put the piece on the bottom shelf of my drying area and promptly forgot about it.

Ginormous Cottonwood Leaf Bowl/Basin.
For some reason, this time it worked!  There were no stress fractures at all when I pulled the leaves off.  I cleaned the piece using synthetic steel wool and bisque fired it, letting it cool completely before opening the kiln.

I used my typical process to glaze it, staining the inside of the piece to bring up the leaves' veins, pulling off the excess with a damp sponge, and applying wax resist before glazing the exterior.  I wanted to fire the piece upside down so there would be no stilt marks, so I took a small, very clean, kiln shelf, put it on three four-inch kiln posts and turned the bowl over on top of it, so the inside of the bowl, with the stained and waxed leaves, rested on the shelf.  (It is very important that the entire inside of the piece be absolutely clear of any glaze.)  I fired the kiln as usual and waited until the interior of the kiln was within 20 degrees of the ambient temperature before opening.

It worked.  It was great.

So, bolstered by my positive experience, I tried another Redbud bowl.  Which cracked.  Again.  So, I realized two things:  (a)  The fabrication process changes may have helped with the structural issues; but (b) They had not solved the entire problem.  I decided to be extremely patient.  I fabricated the piece again, as I had the Cottonwood bowl, but applied wax resist to the exposed clay edge where I had cut out the leaf margins.  I then put the piece even further away in the studio, where I wouldn't look at it for several days.  When the piece was sufficiently dry that the leaves were pulling way from the clay, I removed the leaves and applied wax resist to the upper surface of the piece, putting it back where it had been.  When it was dry enough to pull it out of the mold, I signed the underside, replacing it until it was bone dry.  Although I haven't done anything more with this piece as yet, there are no cracks.  So far.

Stay tuned!

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