Wednesday, October 6, 2010

The Test Panel

I liked the look of the large candlebox and wanted to do another one.  I bought a beautiful deep blood-red glass that I wanted to use for it, but unlike the yellow it had no milky elements to it, it was perfectly clear with just a mottled surface texture.  This meant that if the glass cracked it would be particularly visible.

In my construction experience I'd heard of non-shrink concretes and grouts and decided to use one of them for the new cast.  I built the mold, more or less identical to the yellow-glass one, although the pattern of webbing between the glass panes is different.  I deliberately made it simpler with fewer strands, using the classic artist's mantra, "It's not about what else you can add, it's about what else you can take away".

Before I poured the non-shrink material in the freshly built mold, I first built a mockup of a single side of the new mold, one panel, one face.  My plan was to cast this one side out of the same material and watch it to be sure it didn't crack.  Only then would I cast the larger piece. 

I waited a full four weeks and no cracks appeared so I thought I was safe and went ahead with casting the large red candlebox.  The next day the sample cracked.  Over the next few days, the glass cracked substantially, and even broke through and cracked one of the thick side elements.  I was disappointed, but it was a good experiment.  Even non-shrink concrete apparently shrinks a little bit.  On the upside, the cracks are finer, the concrete finished smoother, and it generally has a nice surface appearance.

Also as an experiement that I haven't yet repeated, one section of the panel was cast without glass - hence the recessed concrete shape in the center.  I like the idea of not having glass in every panel.

This test inspired a design for a full-sized concrete-encased stained glass window.  This design has not yet been executed.

Large Concrete Candlebox

Cracking was an issue for the small and medium concrete boxes so I decided to go larger, still thinking that the heat of the flame was causing differential expansion in the materials.  These candleboxes are 6" square, and 7-15/16" tall.

The thick solid edges of the cube on the smaller model were too similar to the web of concrete between the glass elements, so in this design I decided to make them more organic and curvy to further articulate the difference between the edges of the cube and the surface of it.

Large cube next to a medium one.

The molds for this cube were complicated and took about ten hours to complete.  You can see the glass already inserted into the molds below.  Each of these panels is then turned on edge, and concrete fills the space between the panes, holding them in place.

The cross visible in the mold below is the formwork for a slot in the base of the mold.  The medium and large candleboxes have slots cut through the bases in order to allow for more air flow.

The horizontal ribs are just reinforcement to keep the form from blowing out under the pressure of the concrete.

Just like the previous candleboxes, while it came out of the mold beautifully within two weeks it began to crack.  Shortly thereafter, the concrete itself began to crack.  It was then that I realized it wasn't the heat of the candleflame that was doing it, but the concrete itself.  Normal concrete shrinks as it cures, taking anywhere from four to six weeks.  As it shrank, it compressed the glass (which doesn't shrink) cracking it.  But the glass has no where to go, and will only give so much.  When it reaches its tolerance, the concrete around it cracks.  This realization made me explore the use of non-shrink concrete.

The large candlebox with red glass was cast with the same non-shrink grout as the test panel and the red glass small candlebox.  It's the best example of this kind of work I've done so far but it still experienced cracks less than a month after de-molding.

Concrete Business Card Holder

The architect Louis Kahn once famously remarked that he asked the brick what it wanted to be, "...and the brick said, 'I want to be an arch.' I thought I could do the same thing as an arch, span an opening with a lintel that would be cheaper, and the brick said, 'I want to be an arch.'" Frank Lloyd Wright had a similar idea in mind when he wrote that new materials require new forms.  In the spirit of Kahn, I asked concrete what it wanted to be and it said, "I want to be a cube."

Because all of my concrete casts are subtractive (I start with a fairly pure shape, box, etc) and then subtract pieces from it to end up with the finished form, I thought it would be interesting if the cube that the concrete wanted to be had recessed sides, a concrete crystal.  The ongoing design idea then becomes that just like all crystals on earth - they have a pure form, and as they react to their environment they grow in peculiar ways.

The concrete candleboxes shown in earlier posts could be considered the concrete crystal's reaction to candlight - where it grows thin enough or slotted to permit light to pass through.  The stacked cubes of the lamp grew to hold the bulb off the table.  The crystal forms of the fountains grew in response to water running over them, etc.

This was one of the simplest and earliest tests of the concrete-as-cube idea, a slotted pure 3" cubed form meant to hold fifty or sixty business cards.