Yay! Thanks for the dig @amd !
It does look like an impression mat indeed! As for the planing.. yes, maybe. Planing and painting could explain the stripes and unevenness of the color on some of the skulls that make them look more ghost-like. The upper edge of the single bar also looks like some color has been planed off, especially compared to the freshly cut picture. Though I'm wondering if both pictures are from the same batch or if there is just a slight difference in pour and color between batches.
It does look like an impression mat indeed! As for the planing.. yes, maybe. Planing and painting could explain the stripes and unevenness of the color on some of the skulls that make them look more ghost-like. The upper edge of the single bar also looks like some color has been planed off, especially compared to the freshly cut picture. Though I'm wondering if both pictures are from the same batch or if there is just a slight difference in pour and color between batches.