Materials Witness: Casting in the forge at UC

Monday, November 17, 2014

Casting in the forge at UC

First, a mention of thanks to Abby Friend, Princeton High School graduate in the class of 2011, and a current student at the University of Cincinnati in their DAAP (Design, Art, Architecture, Planning) school. An additional mention of thanks to Farron Allen, professor in the DAAP school who allowed me to hang out in 'his' forge for an evening class.

The students had previously made their investments out of ludo, plaster, and silica sand, burying wax sculptures and - in some cases - tiny, plastic doll limbs in their investments and ensuring that their hidden treasures had enough sprues attached for the bronze to find their way to every inch of the creations-to-be. I don't have any photos of that investment process, though you can see the final products in the large, white molds into which the bronze you see below is being poured.

Abby explained that much of the investment is reused - mixed with new plaster and sand to be used for the next set of investments.

On to the casting...


Those are the investments to the right. They just came out of the really large kiln. The bricks were on top of the holes to keep any dust out of there. The green flames to the back were coming out of the methane-fired kiln in which a whole bunch of bronze was melting in a ceramic crucible.

Here Farron (I feel weird calling a professor by his first name, but that's how Abby referred to him, so I'll go with it) was adjusting the gas and air to make sure the fire is right. No temperature was being measured here. It was done all by sight. Eventually Farron did check the temperature once.

Farron and two of his students were preparing to lift the crucible out of the kiln.

The crucible's weight was almost entirely handled by the crane - yellow thing in the left edge of the photo, chain sticking straight up from just in front of Farron's hard hat. The sight of the kiln was gorgeous and bright enough that my phone's camera couldn't do a great job of white balancing the photos.

The first investment was filled. The weight, again, was still held by the crane, but the control of the pour itself came from the student on the right who tilted the crucible by a distant hand. Farron was pretty solidly directing the aim of the crucible.

closer view of the second pour...The thermometers that went into the molten bronze can be seen just behind Farron's upper hand with large, cone-shaped heads and long...um...other parts to go into the bronze and keep the measurer's hands far from the around 950C molten bronze.

You can see the handle that allowed the student on the right to control the speed of the pour.

Here the crucible has been out of the kiln for a while, so it wasn't quite as blindingly bright. The molten bronze, though, was still pretty darn hot.

After the first batch of bronze was poured, Farron put the crucible back into the kiln and reloaded it. Notice here that the fire isn't green yet. It's not quite hot enough yet to get the vaporized copper atoms that change the flame's color.

The crucible was coming back out a second time. So hot, so bright...

The crucible was initially set upon a pallet of bricks onto which was set a number of layers of newsprint. The newsprint immediately flared leaving a layer of carbon between the crucible bottom and the bricks. Abby said if that newspaper wasn't there, the crucible would have fused to the bricks or cement or pretty much whatever the crucible was set upon. Sadly I didn't know that in advance and missed the flare opportunity.