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Janel

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I have to ask you Tom Sterling, what are you using to create the clay to metal lid on? Also, can you show us more about that material? Is it as carvable a clay? Does it hold detail when fired? Do you carve it more after firing? Do you use an electronic timer to do the up and down phases of firing?

 

Questions questions!

 

Janel

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Hi Janel,

 

I put a short discussion of PMC in the Show and Tell section, titled One if by Land, Two if by Sea that provides a basic description. To further refine that and answer your questions: I rolled a thin sheet of the PMC clay out on a polymer clay slab that I previously made on a piece of rough wood (for surface texture), cut a two inch circle and used a highly technologically developed forming device - a burned out light bulb held in a cardboard tube so it would stand up. This gives me a round, domed sheet to build the organic forms on. The light bulb, rolling surface and tools, and my fingers are coated with an expensive and rare mold release compound (olive oil) to prevent the clay from sticking. I dried the clay dome on the cardboard/cardboard tube for about an hour in a 180 degree (F) kitchen oven, and sanded the bottom edges flat. Then I took some more thin sheet and a cardboard template in the shape of maple seed helicopters, cut out the basic shape with a scalpel, and glued the wet clay sheet onto the dried clay dome using gooey slip (more PMC mixed with water). For each of the helicopters, I added another small blob for the seed, a long string for the leading edge and then smoothed everything together with a rubber tipped cone shaped pottery shaper tool, forming the ribs as I went. I put the whole thing back into the warm oven for another hour to dry.

 

PMC isn't as nice to form or carve as porcelain clay is. It's more like chewing gum (that's what it looks like just out of the package), and doesn't seem to go through that nice leather hard carving stage. I tend to form the shapes as well as I can while wet, then use my micro grinder and diamond sanding burrs to carve more when the everything is dry, but before firing. Unlike porcelain, the clay doesn't shrink while drying so you can add wet to dry, dry to wet, and even embed things into the clay to either burn out during firing and leave voids, or be trapped in the clay if they aren't things that will burn. Quite forgiving in that sense compared to conventional ceramics. Completely hollow forms are possible, even without vent holes, again unlike ceramics.

 

I fire the PMC in a small kiln (with digital controller) at 1650 or 1750 degrees (F) (depending on what version of PMC I've used). If the 1650 version I fire for two hours, if the 1750 version then 30 minutes. Details remain absolutely unaltered, unless you fire too high, in which case you get a molten pool of silver with no detail at all. The 1650 version shrinks about 25%, the others about 10% during firing. Supposedly you can use a standard non-digital pottery kiln with pyrometer if you watch the temps closely, and there is a torch firing method I've not tried. Up and down phases of firing are really simple, unlike conventional ceramics - full rate up, hold for the prescribed time, turn off, when you feel you can open the kiln without blinding yourself, fish it out and quench it in water. As previous-potter Janel well knows, don't try any of that with porcelain...

 

I use a hard, smooth steel object to burnish the surfaces that need to be smooth/shiny after firing. The silver is pure white when removed from the kiln, becomes silver/shiny if burnished. I use scotchbrite pads (maroon) in a grinder for general cleanup to remove the white look. Once fired, you can file, grind, polish, hammer, solder, etc, although I generally don't do any of that. since the metal is actually sintered, it isn't as dense as conventionally cast silver, and won't take quite as bright mirror polish.

 

I've cobbled together a before and after image below. On the left is the dry but unfired piece (2 inches in diameter) on the light bulb. On the right is the fired, burnished, polished and patinated piece, ready to be inlaid in a wooden basket lid. The two are in approximately correct size ratios. I began the piece at about 10 AM, and finished it about 6 PM the same day. Four of those hours were either drying or firing.

post-11-1125716203.jpg

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Hi Tom,

Thankyou for the information on the PMC. I have wanted to try the material but didn't know enough about it to give it a try. Thanks to your detailed lesson I think I may give it a shot. I have had some pieces done by the sintering method. I am posting a picture of one of them. This piece is 4" high by 14" long and is bronze.

Thanks again.

Dick

post-15-1125755366.jpg

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Hi Dick,

 

Good to hear the PMC info was useful. Now, for my question - sintered bronze - way cool? How do you/they do that? Assuming this isn't "cold cast," I take it the bronze sintering method isn't something the average small art studio can do. Do they need vacuum, exotic gas or oxygen free casting atmospheres? And what foundries do it? I haven't seen it offered at the foundries I know of (but that's not saying much!).

 

Thanks in advance.

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Hi Tom,

Sintered bronze is a bronze powder mixed with a wax base. The material is poured into a silicone rubber mold when cooled placed into a kiln and fired like the PMC material. Large pieces can be cast. Industry uses the process all the time but the only "art foundry" I know of was in State College PA. It went out of business a couple of years ago. I wish I knew of a another "foundry" but I don't. If anyone reading this knows of a place please let us know. As you can see from the picture of the sculpture the process gets 100% of detail and costs about a quarter of regular bronze casting. The pieces will break if bent too much but the material will allow brazing without melting. The patent for the "art process" is held by a Professor at Penn State. I gave them a clay and in about two weeks I picked up a finished bronze and the mold. The origional clay was destroyed making the mold. I think they can make the PMC in bronze but couldn't charge as much because it dosen't have silver or gold. I wish I could help more.

Dick

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Thanks, Dick - imagine a foundry charging one fourth of their usual charges! Boggles the mind, the economic possibilities...

 

I've watched "flat" artists with envy for years with the ever cheaper means of producing (and selling, let's be honest) print multiples. I've spent lots of effort looking for a similar means in 3D, but the closest I've come is a very limited and high-effort overhead in ceramic and PMC molds, since bronzes are so expensive to produce, and with such an up front financial burden carried by the artist alone. And I can't stand the thought of the plastic cold-cast stuff.

 

PMC has worked out the best for me, since my experiments with ceramic molds sold OK, but not eye-watering, and there was a huge amount of cleanup and additional carving just to get close to what I wanted. Wood/ivory/antler was more rewarding, at least carving wise. Maybe my standards are too high!?...

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Hi Tom,

Have you thought about casting a piece or pieces in pewter? You can cast pewter in silicone rubber molds using gravity and get a perfect cast every time. The pewter is solid metal and can be burnished to a very high polish. I have molds that I have used to cast hundreds of pieces of sculpture. You can even make fairly large pieces by doing them in sections and soldering them together. I do a piece for Christmas every year to give to friends and relatives. The pieces I do are about four inches high and the mold costs about $20.00. You can buy pewter at around $5.00 a pound depending on the cost of tin.

Dick

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Hi Dick,

 

Yes, I thought about pewter, but finally decided it just didn't have the, shall we say, "client recognition" (pizazz!) that bronze, silver, gold or the Japanese alloys have. It just didn't fit my personal idea of the level of my (desired) market. Good thought, though!

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