I conducted a very scientific experiment on the walnut natural satin durability.
I prepared my cappuccino in my favourite cup gifted to me by the lovely barista I helped one day. The bottom of this cup has a Mohs hardness of 7. The bottom was 78C and was circumscribed by 0.5 mL of water moisture. I slid it across the walnut at an acceleration of 1 ft/sec^2. I left it on there for 5 mins. I then removed it and wiped the moisture. I saw no visible change in the walnut.
Photos below. All very scientific-like. I let my cap get cold in the name of science!
I declare this walnut natural satin pretty darned solid. We'll see how solid the future subs are.