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To make a sculpture, I begin by contemplating a shape: maybe a familiar solid such as the cube, or a more esoteric one like the rhombic dodecahedron or one of the zonohedra.  Using modeling clay or whatever is handy (paper, toothpicks...), or maybe just visualizing mentally, I think about it and develop possibilities, and eventually something emerges that will be interesting to build.  Often I begin to approach something that I can't visualize or model directly - maybe I see it indirectly by abstraction, or I can see only part of the whole.  Those are the most interesting cases, when I'm building the sculpture in order to find out what it looks like.

Once I have a model, whether it's in hand or in mind, I work up the design using CAD software.  My usual tool is Rhinoceros, which is a 3D modeler for Windows, but I'll use anything that seems useful.  Often I'll put on my programmer hat and write a utility to help things along.  I wouldn't say that being able to code is central to my work, but it's a handy tool to have in the box.

A typical plasticene maquette.  Notice its
untidy appearance - there's much to
clean up as the design goes digital.

Wireframe view of the design for AlterKnot.

3D modeling, at least for me, is a tedious, technical process.  It's still a big timesink, and when I was getting started the learning curve was steep.  It isn't helped by the sad fact that scanning technology can't (yet) handle the undercutting and interlacing found in my work.  This means that even if I've got a good physical model, it must be completely rebuilt as a virtual object, because there's no way to scan it in.  I do use a Microscribe digitizing arm to help get my maquettes into the computer, and that saves time.

The next stage is to get from the virtual model to a physical object.

 


 

As I write this, I'm making things mostly by direct-metal printing: there's a machine that takes a CAD file specifying a 3D object, and builds the object, physically, as metal.  If this sounds like science fiction to you, well it might. 

I don't (yet) have this machine on my desk, I just rent time on it.  The process that I use is proprietary to Ex One, and they do the printing.  What follows is very much a layman's explanation of how it works -- for more technical information, please visit Ex One's site.  (Some information about other types of 3D printing is here.)

To start with, the design is laid down, one layer at a time, in stainless-steel powder held in place by a laser-activated binder.  You can see the layering on the finished pieces, it is the source of the characteristic texture of my work.  Each layer is .004" to .007" thick. 

The steel granules are so fine that they feel like very heavy, cool flour.  During the build the extra unbound powder supports the piece, so no extra structure is needed to handle undercuts.  The powder is very flowable, it's not caky like cornstarch, so removing this extra supporting powder from the finished model is quite easy.  It slides off with a little shake and a light brush, and it can be poured out of interior spaces. 

After the whole model is built up, and the extra powder is shaken off, the piece goes into an oven, where heat drives off the binder and fuses the steel powder.  There's just enough heat to make the granules weld together where they touch, without collapsing the entire piece into a puddle.  This produces a porous steel part that's about 60% dense, like the one at left. 

This "green" material is matte gray, feels like sandstone, and won't take a polish.  It is soft enough to cut quickly with a hacksaw, but can't quite be dented with a fingernail.  It's considerably lighter than steel, which is not surprising since it's 40% air.

At right is a shot of Nexus as a green model.  You can see that two extra stems have been added onto its corners, and now they come into play: to get rid of the porosity, the airspace that remains in the piece will be replaced with liquid bronze.

To do this the model is heated again, the stems are dipped in a crucible of molten bronze, and capillary action causes the bronze to wick throughout the piece.  It's completely counterintuitive that this works -- I think this must be the main reason why Ex One has this patent, and we don't. 

Impossible as it seems, the end result is a composite metal that's fully dense, with properties intermediate between steel and bronze.  It can take a polish or a patina, developing either rust (on the steel) or verdigris (on the bronze) depending on the chemical environment.  Once it's been initially passivated, the metal seems fairly stable in a household environment.

At left is some raw material as it comes from the shop, showing the original look, and an area that has been cut and polished.  Although the metal is tougher than bronze, with some elbow grease I can work into it: I use carbide bits to cut it, and the hardened files that are made for working platinum.

The color varies between builds, with some parts quite bronze-colored, others looking almost like pure steel.  (Everything 3D-printed is called a "part" in the industry; my work is referred to as "art parts".)  Occasionally I get a batch that finishes out with a layer of pure copper on the surface, as though it's been flash-plated.  I suspect it may be a chemical thing, something like the way pickling sterling creates a layer of fine silver, but it's all very mysterious to me.


 

A raw model is far from a finished sculpture, but from here on there's no interesting technology, it's all traditional. 

I start by chasing and retexturing the stems that were used for bronze infiltration, using hand and power tools.  Then I oxidize the bronze to a nice brown color, using heated sulfur and ammonia compounds to darken it.  As you might imagine I can't do this part indoors, since it develops some remarkably unpleasing odors.  I keep the steel from rusting by using very hot dips and drying immediately with a heat gun, so the metal isn't wet for more than a few seconds at a time.

Next I remove most of the oxidation by tumbling with abrasives, which smooths the corners and the roughest parts of the texture.  This also brightens the high points, while leaving color inside the texture. 

Lastly a burnishing tumble with steel shot puts a shine on the piece, followed by a light oil dip to seal the surface.  And there it is: another fine work of art by me. 

 
A couple of older pages in this area are about lost-wax casting and other types of 3D printing.  They concern technologies which I'm not using at present, but maybe they'll be useful references.