Primer for this blog
- Copper is a natural element.
- An alloy is a mixture of two or more metallic elements.
- Bronze is an alloy whose primary element is copper.
- There are over 400 different alloys that qualify as bronze.
Now, our story:
In 1996 Desert Crucible cast a monumental sculpture titled “Exchange at the Presidio”, which the Mormon Battalion Monument Committee donated to the City of Tucson. It is a depiction of an unusual event that occurred in 1846 during the Mexican-American war. The US Mormon Battalion was on an arduous trek from Council Bluffs, Iowa, on its way to San Diego (at that time a part of Mexico), to reinforce US troops.
The walled pueblo of Tucson was under the protection of a Mexican garrison. The Mormon battalion was in rough shape from the journey, and badly in need of supplies.
Rather than what could have been expected to take place (a clash between the two military groups whose countries were at war), a remarkable temporary rapprochement ensued. The Battalion entered Tucson, and a critically essential bartering took place where European cloth from the officers uniforms were exchanged for vital supplies. There were no hostilities, and the Battalion continued on to San Diego.
The sculpture, standing nineteen feet tall and weighing about two tons, depicts an officer and an enlisted man from the Battalion exchanging goods with a Tucson merchant.
The sculpture was cast in many separate pieces, most of them weighing less than 100 pounds, and welded together.
Finally, the point of our story.
When casting and assembling (welding) the individual pieces of a monument, it is essential that each piece, as well as the welding rod used in their assembly, be of the exact same metal alloy. Different alloys weather differently, and over time, if different alloys are used, the welding seams and the different pieces will begin to look like a metallic patchwork quilt rather than a single, monolithic structure.
Our alloy of choice, chosen for a variety of technical considerations, was Silicon Bronze, or 95-4-1. It is a composition of 95% copper, 4% silica, and 1% other trace elements.
During the production of this sculpture, the Committee received a very generous in-kind donation from the copper producer ASARCO. It was delivered to the door at the foundry. It was a copper cathode (one of those thick copper plates you sometimes see stacked end to end being transported on a railroad flatbed), about 36 x 36 x 1/2” in dimension, and about 275 pounds in weight.
We were thus presented with a dilemma. We had no way to alloy such a large chunk of pure copper into silicon bronze. Our only option was to take the donated anode to a metal scrap dealer, sell it, and use the proceeds to purchase from our regular supplier the silicon bronze ingot we needed.
This we did.
A couple of weeks later, here come ‘da fuzz – two dudes in suits with official credentials ready to arrest whoever stole the anode and sold it to the scrap dealer. The check from the dealer had been made out to Desert Crucible. Wait a minute. Nobody stole anything. That anode was a donation. Papers? No, no papers. It just showed up at the door. Yeah, right. It took a while, but we finally got it all straightened out. One more episode in our finding our way through the inevitable bureaucracy of the day.
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