BRONZE CASTING PROCESS: POST 7
So, a bit of a preamble. Here we are, stuck at home, self quarantining. At home is my default position, and people usually help me quarantine when they see me. Six feet is about as close as most folks get if they spot me first. It is kind of like a halo I’m wearing, only much more ruffled up and encrusted with the trappings of a sculptor. Think Charles Shultz’s character, Pig-pen. I’m used to air hugs that look more like a football coach protesting a referee’s bad call. But these are unique times for us in this country, and we have to look for the good in the bad. It is not all bad for us to take some time away from the hustle of modern life, and take a look around at how we are living. There are people who cannot afford this down-time, for lack of a loaf of bread, and there are people who have more than plenty, that really need some down-time to consider what is important that they may be getting wrong.
Most of us self- employed artist types likely find ourselves somewhere closer to the “can’t afford” end of the spectrum in terms of the security of a career in art. It is a famously fickle business. But at the same time, many of us should sit a spell and look at what sorts of things fill our days. What sorts of things are we doing that we take for granted as part of our days, yet we may not even want in our lives? What things of beauty are we missing? So, for me, I am seeing that, yes, I like doing what I do for a living, and I have loaves and loaves of bread. Sometimes I can forget that, amongst the dust and the noise and the nitpicking tedium of some aspects of this job. I live in a beautiful part of the world, and get to share it with some amazing people who are generous and curious and creative and thoughtful and strong. I hope wholeheartedly that these times are kinder to us than what we might fear. In my selfish way, I hope that at least my many friends and neighbors come out fine. Even now, we know that so many folks already have had those sorts of hopes dashed. I send my sincere wishes for your good health and safety, wherever you are, and whatever your challenges. We see the same bright sky, and at the same time, feel the losses mounting around us.
Here’s to hopes for a silver lining, a few things learned, and an enduring spirit of living in an amazing and powerful world of never ending intrigue and beauty. There is this price to living, and it is my hope that for those who’s chips are called in, that they can say, “What a marvelous trip!” For those who are fortunate to not suffer loss in these times, it is perhaps a chance to look around, see things in a new way, and appreciate what we may have been taking for granted. And while we are looking around, maybe we see someone who has not fared so well, and we find ways to be helpful.
Now with those sentiments shared, for the sake of something to read, should anyone be bored enough to choose my little rant, onto the subject of the process of casting……
When the casting molds are good and dry, it is time to melt the wax out of them. This stage is called burnout. No, not the kind you are experiencing with this tedious tutorial, but rather the kind with FIRE! Each mold is placed in the burnout oven where it will be melted clean of wax. My burnout oven is powered by propane, and made out of scrap iron junk, and lined with refractory kaolinite wool. As the wax melts, it pours out into a pan on the outside of the oven.
(The wax is entirely reusable. I get nearly all of it back after each use, and have been using the same supply I started with almost twenty years ago.) I continue the burnout until all of the molds are melted clean. It is exceedingly common that the molds will crack in the oven as the wax heats and swells against the ceramic shells. Usually the cracks are small, and easily repaired with refractory cement.
After everything is in good order, with the molds clean of wax and repaired, it is time to PLAY WITH FIRE! Real fire, this time.
The molds will first be positioned in a preheat oven, and they will be heated to a pink glow. My preheat oven holds three shells and is made of…okay, yup, scrap iron junk. It is lined with kaolinite wool. I heat the molds to perhaps 1600 Fahrenheit.
Meanwhile, the bronze, which comes in twelve to fifteen pound ingots, will be melting in the furnace. I made my furnace out of Mizzou refractory cement, and you guessed it, a bunch of scrap iron junk. It will heat 90 pounds of bronze to a pouring temperature of 1965 Fahrenheit in about an hour and a quarter.
The ingots are placed in the melting furnace inside of a “gin-u-wine store-bought” crucible made of graphite and other refractory materials. The crucible is designed to withstand the heat and hydraulic pressure of the molten metal. Water weighs about 62 pounds per cubic foot, and bronze, about 540 pounds, so the hydraulic pressure in a crucible of metal is quite considerable. If you imagine a bucket of water with a crack in its bottom, the water wants out through that crack, and it wants out fast. If the bucket is full of molten bronze, it wants out almost ten times as badly. (That is nearly like your wanting out of this thing you are reading. But you can just quit if you want to.) The 2000 degree metal flowing from a cracked crucible does not quit until it is all on the floor, melting the soles off your shoes, and frying your feet into shriveled strips of dried meat, all the while, exploding like small volcanos from the moisture trapped in the concrete floor. The viscosity of bronze at the pouring temperature is far more liquid than one might expect. On one occasion, when a mold broke as we were
pouring, the metal ran out through the preheat oven and along a hinge of the oven door. I figured that the bronze, once solidified, would peel away from the hinge like that stupid smirk I had just been wearing, thinking I’d had another successful pour, but not so! It was liquid enough to run into the hinge and form a sleeve of bronze the entire length of the hinge pin. It took eighty or ninety swear words and several hours of bashing and grinding on things to get the door working again. So, while spills have been rare, and never due to a broken crucible, (knock on graphite), caring for the crucible is an important item to keep in mind. It is inspected before every pour, and heated evenly and slowly, and stored high and dry when not in use.
The only time we have had a crucible break was when I had failed to bring it inside after an outdoor pour before I’d built my foundry building. It had rained, and several inches of water had funneled into the crucible. I thought that it would dry out eventually, so I sat it on my wood
stove in the shop for about two or three months through the winter. When I decided it was probably good and dry, I put it back in service. I put three ingots in it, and started the furnace. Everything seemed good to go, so I cranked up the fire, going for a melt. All was quiet for
about thirty more seconds, and then what sounded like a close range 44 magnum shot rang
out! I looked around in several directions for enemies, and then into the furnace. The crucible had exploded like a steam boiler! Fortunately the melt had not yet begun, and so the three ingots were just sitting there in the bottom of my furnace, amongst the rubble. As you might imagine, my junior foundryman’s badge was recinded for several weeks, and I bring my crucibles into my main shop after every pour, storing them high and dry!
Anyway, when the metal is ready to pour, the crucible is lifted out of the furnace by heavy tongs, and then set into a pouring shank. These items were made of scrap iron, in case anybody is wondering. The pouring shank allows the crucible to be lifted from low on its sides, and thus tipped and emptied into the casting molds. Tori is usually on one end of the tongs and shank, as she has powerful and intimidating biceps. Anna Richardson or Coco Forte, our fellow pyromaniacs, “gag” the crucible, holding the scum from the melt, such that it doesn’t
flow into a mold. If all goes well, the terror that accompanies almost every pour slowly subsides. The metal will cool in a minute or so to a solid state, and if that is all you are casting at the time, you can have a beer! No one with a brain would drink alcohol and then pour metal, but after a pour, it tastes pretty good. All of my help is immensely appreciated, and is
paid a drinking wage while on the premises, but not a living one. I was dutifully instructed by my old college professor, Judd Koehn, that to appease the fire gods, one should never skip
the beer stage of the casting process, and as a rule I don’t. I’ve skipped it a time or two when we have had to pour metal in the morning, but are fire gods early risers? I just don’t know. Our preferred time to pour is in the afternoon. It is better in the afternoon, when a beer seems more appropriate.
If this process has a seat-of-the-pants feel about it, you are forgiven for thinking that. Nothing but the crucible was engineered by anybody other than myself, and I am in no way an engineer. But everything I’ve cobbled together has worked fine, and with a few alterations now and then, it has come to be a relatively problem-free process. I might be no authority on foundry principles, but I am the world’s leading authority on my foundry! That is both comforting and frightening to ponder….
