Five knots are bent into the shape of a larger knot, the symbol for infinity. The five knots are the same, with different degrees of distortion and smoothing:

The infinity symbol is really just a loop with one twist. The smaller component knots are loops with three twists.

I charred the fir (the dark backing behind the copper) and brushed it with a brass wire brush several times. This transfers a tiny amount of the brass into the wood and gives it an unusual shine.