BRONZE CASTING PROCESS: POST 8
As we continue our social distancing as it has come to be called, I find it a bit hard to focus on what it is I am supposed to do. I am infinitely more fortunate than many, if not most people, to work in isolation as a default position. If I am not alone, the chances are that I am playing hooky from my work. In that way, art is sometimes a lonely business. But then there are the times when it is a business more fitting for the extrovert, as during gallery openings. It surprised me to learn that there are muscles in the face that get tired when all you are doing is smiling and talking with people for hours at a time, and it can be a relief to get back into the shop. But with these uncertain times, shows are off, studio visits don't happen and there isn't much connection to the people I do my art for. But being alone is part of the process of having ideas to make art about. I hope that for those of you out there who have an interest in making art, as well as experiencing the art of others, that this is a time for making something that your busy life seldom allows time for. The rewards are in the form of having accomplished something, and maybe in sharing ideas with others when you have an image to share. I hope you all, and those you hold dear are safe and well in this strange time. Many of us are cooped up, and though it is our duty to keep our distance, it doesn't feel particularly useful doing so. But to those out there on the front lines, caregiving, I am sincerely grateful. They are the hero of our times.
Now on with this process stuff. It is getting close to the end! We left off with a bunch of hot metal, just having been poured into the ceramic shells. I think we were drinking a beer.
Once the metal has cooled, and the fun people have all gone home, it is time to begin the drudgery of shell removal. This process is called “chipping and blasting”. Since the bronze shrinks as it cools, the shells will have cracked to some degree. Still, a certain amount of beating and swearing is in order to loosen the ceramic material from the casting. An air chisel is the normal go-to tool to get rid of any stubborn pieces of shell. When the casting is reasonably clean, it will be sandblasted to a clean golden luster.
At this point the art work parts of the tree can be cut loose from the sprues and vents by means of a plasma cutter. In a commercial foundry this whole chipping and blasting job is relegated to one of two types of people. Generally speaking, the new guy is who we are talking about, but in a pinch, the foundry manager will select someone that either doesn’t have a brain, or doesn’t use the one they have. I don’t mean to say that this work should be done
with a mindless zealotry, as an otherwise beautiful casting can be colossally messed up by a careless guy with an air chisel. But the point is, this laborer will either shape up, or quit after a day or two of chipping and blasting.
Of course chip and blast men come and go, but the one thing they do not do is stay. Dwelling at the bottom of the hierarchy in a foundry is hopefully a transient condition, and so a never ending stream of new unsuspecting people must be recruited for this glamorous job. Among the factors complicating moving up, however, is that brain cells can be visibly observed shedding away, even through all the protective clothing worn for this work. A new employee who walked in the front door with an IQ of 160 will generally walk out the door at the end of the first day with and IQ of about 40. The only real saving grace for these poor souls is that having shed those brain cells that are not specifically dedicated to simple survival, they are able to concentrate their remaining cells on getting out of that chip and blast room.
Fortunately my chipping and blasting never consumes any whole day, but rather, only an hour or two every few weeks or months. So while my IQ is falling about 10% per hour, (or about 6 points) I am soon done with this work, unlike the chip and blast man at a typical commercial foundry, rattling away for eight to ten hours. And starting over with an IQ of 54 or even 48 is better than starting over at 40. Higher function of the brain returns after several days of stupor. Or so they say...
The next step in making this bronze sculpture we’ve been working on is cutting the artwork from the feeder tree. A plasma cutter does this nicely. It burns or melts out a kerf in the metal like a water pistol blowing a stripe out of your soft ice cream cone. This goes pretty fast, and when you are done you have a nice pile of sculpture parts to clean up and assemble. Clean-up involves close-cutting all sprues and removing any casting fins or bubbles that may have formed in the slurry process. These bubbles end up as metal where air was trapped against the wax. I usually sand all the parts before assembling them, as they are smaller and easy to handle. When I start welding things together I like to have very little clean-up of the casting left to do.
Once everything is welded together, the welds will be cleaned up with grinders and sanders to resemble the original textures that have been disrupted in the casting process. Most of the grinding is done with pneumatic grinders fitted with carbide burrs, or with flex-shaft tools and dental burs. Welding bronze takes a special welder call a TIG. (Tungsten Inert Gas) A MIG is also used by some foundries for very large works. (Metal Inert Gas) The inert gas is generally argon, which shields the weld area from oxygen, allowing a clean weld to occur by means of an electric arc and non-fluxed filler rod. TIG welders are used for many welding applications where the weld needs to be very clean and very strong, as the arc can be forced to penetrate deeply into the metal. But most frequently TIGs are used on non-ferrous metals and stainless steel.
Welding is its own subject, beyond the scope of this tutorial, and aren’t we all very happy about that?! But suffice it to say that all of the joining of the cast parts is done with a welder, along with putting together any fabricated parts the piece may have.
After the work is fully assembled and the welds have been tooled and sanded the piece is ready for the final coloring or patina.