The pillars are mostly HA. I replaced the face motif on Hirst's capitals (2 per 90°) with my own sculpts (3 skulls per 90°, 12 unique ones) and made a mold. The lowest level of the pillar base is made out of pine from Kapla blocks.
Image originated 2016-07-09T12:50:56+00:00.
Viewed 2018-07-17. Ugly in unsafe old browsers.