One of the intriguing announcements at Apple’s Spring Forward event last week was that the Apple Watch would be offered in a variant encased in 18-karat gold (Apple Watch Edition), and will sell for US$10,000 apiece. While the timepiece itself was hailed by many critics, the gold variant elicited a negative reception. Business magazine Bloomberg Businessweek published a scathing review, putting Apple right up there with Gucci as a luxury brand. Actress Anna Kendrick weighed in in much blunter terms, branding the gold watch the “gold standard in douchebag detection.”
Apple posted a two-minute video on its website recently, in which VP-Design Jonathan Ive narrates the gold manufacturing process. Pure gold is a rather soft, weak material compared to other metals, with a yield strength of 30 MPa and a Vickers hardness index of 25 (by comparison, 6061 age-hardened aluminium yields at 250 MPa and has a Vickers hardness index of 100).
Apple therefore uses an 18-carat gold alloy for their watch case. Alloying essentially means that atoms of other elements are introduced into a gold crystal lattice in order to improve its mechanical properties. By definition, 18-carat gold must be between 18/24ths and 19/24ths gold by weight. In Apple’s video, Ive reveals that the alloying elements which fill out the remainder of the weight are silver, copper, and palladium. In other words, some of the atoms in a gold crystal are replaced with atoms of silver, copper, or palladium. As these atoms have slightly different sizes, they made it more difficult to break the material (metals, being ductile, fail or break due to atoms sliding past each other). This is created by heating a mixture of gold atoms with alloying elements until they melt, and then pouring it into a casting to solidify into an ingot.
Apple achieved further strengthening of the material by cold rolling it. The ingots, once cooled to room temperature, are passed between a pair of rollers, compressing it to a smaller thickness. This also introduces dislocations by sliding atoms out of their places in the crystal lattice. While too many dislocations can cause the material to fail, a limited number of dislocations actually strengthens the material, as they form barriers that make it tough for atoms to slide any further.
The video shows ultrasonic non-destructive testing being used as quality assurance, to identify defects in any of the gold billets produced. The actual watch casing is then machined with a mill, with computer numerical control (CNC) being used to ensure that the finished product has accurate dimensions. Finally, the case is polished before being assembled to a watch.
In my second year, my class had an assignment where we had to pick a material for a foot bridge across a creek. One of the questions asked us to disregard cost. After looking up a few properties, my group duly recommended that the little bridge be made from Kevlar. Cost: $100,000. What Apple has done with their gold watch sounds a lot like a real-life version of that. They made it, because they could.
Even given the cost of the material and its manufacturing process, $10,000 sounds rather high. But that’s how they roll. Fakers gonna fake, haters gonna hate, and Apple gonna charge ridiculous markups.
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