Caithness flagstone at a threshold has this quiet way of settling an entire entry sequence. The slight ripple in the natural cleft catches the low winter light, and after decades of wet boots, it just deepens to slate-black where people actually tread. Whenever someone asks why we don't switch to something crisper or honed, I take them to the back door of the studio to look at the slab that’s been sitting under the rain since 1890. It does all the convincing for me.