A square of coated glass sagged over a round mould, which is what a fused-glass studio actually makes and why the corners are left standing: glass gives way where nothing holds it up. Look into it and you see both faces of the same sheet at once — the near rim shows you the outside, the far rim the inside — so the colour the coating sends back and the colour it lets through sit side by side, a few centimetres apart. That is the pairing a dichroic stack is named for, and a vessel cannot stage it.