Wednesday, September 26, 2018

What Are Grand Seikos Made Of? Sugar and Spice and Everything Nice?

Dials, movements and watch hands get all the glory, but the steel that watches are made from are the unsung heroes of watchmaking.
Grand Seiko SBGH267

Grand Seiko deploys three kinds of steel in their watches: Grand Seiko cases use 316L steel, the hairspring is made out of Spron 610, and Spron 530 is what you'll find in the mainspring. These steel alloys have special properties that make watches more accurate and robust. Spron 610 resists impact and magnetism better than previous alloys used for the hairspring; Seiko’s Spron 530, which took six years to develop, has the ability to handle greater torque and offer higher power reserves than what came before. Steel isn't sexy (unless you want it to be) but it's what makes the watch hands go round.

But the metal that we watch wearers notice most belongs to the watch case. It's the case that catches our eye -- or catches scratches. It's the 316L steel.

Different watch companies use different stainless steels. Rolex builds their steel case watches out of a metal they call 904L, which Rolex says is the Hulk of steels, only prettier. But contrary to Rolex’s marketing material, their 904L steel is not much hardier than Seiko's 316L when it comes to everyday wear, though it does have better resistance to salt water and chemical corrosion. 904L steel is used in industries which have high chemical contact such as acid and petrochemical storage tanks, which is where it originated from. Grand Seiko could have used 904L steel because Zaratsuing a 904L --giving the watch case that magical Grand Seiko polish and lines-- is theoretically doable by Seiko's wizards. After all, Grand Seiko already cuts and shines even stronger titanium for their ultra-light weight and robust titanium watches. But the problem with using 904L steel is that its gummy nature would make any scratches on the Zaratsued surface deeper, more pronounced, prominent...and sad.

316L is the most commonly used stainless steel in watches. The "L" stands for low, as in low carbon content; there's also 316 steel, which has a higher carbon content. Low carbon steels are more resistant to the gremlin known as weld decay. And now you know something that will make you the life of your next watch party.

Grand Seiko uses a fifteen stage cold-forge process on their 316L cases. The majority of Swiss watches including several major brands use casting, cold stamping, or milling. That’s why Grand Seiko's 316L steel watches look very different from the majority of Swiss watches. It's not your imagination: The material used for a watch's case goes a long way toward giving a watch its special way of catching and reflecting light.

Grand Seiko SBGA373G
Craftsmen trained to execute Zaratsu polishing are tested blindfolded. How's that for expertise? Most of us can't even tie our shoes blindfolded. Zaratsu polishers are are supposed to be able to feel and hear the level of polishing achieved, before their eyes register the result.

One other difference between Rolex's 904L and Grand Seiko's 316L steel is their nickel and molybdenum content. Rolex has a higher amount of nickel and molybdenum, between 23% to 28% for the former, and 4% to 5% for the latter. Seiko's 316L has 10% to 12% nickel content and 2% to 3% molybdenum. Both metals can cause contact dermatitis, a skin allergy, which is one key reason why some watch companies, even the high-end brands, have not switched to 904L. Thankfully Grand Seiko has also perfected Zaratsu polishing on titanium, which is nickel and molybdenum free, so our allergy susceptible friends can still enjoy their favorite brand.

A version of this article originally appeared on the Grand Seiko's Owners Club. You can find out more about the Grand Seiko Owner's Club at

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