Albert Barnes Commentary 1 Kings 10:18

"Moreover the king made a great throne of ivory, and overlaid it with the finest gold." — 1 Kings 10:18 (ASV)

It is, on the whole, probable that the main substance of the throne was wood and that the ivory, cut into thin slabs and likely carved in patterns, was applied to the outside as a veneer. This has been found to be the practice in Assyria. The gold was probably not placed over the ivory but instead covered other parts of the throne.