Mostly airbrushed, with some high contract pin washing and pastel weathering. The base is made from cork, acrylic nail powder, and crushed glass for the snow.
The entire base is covered with a sheet of "ice" made of acrylic. , as are ice-stalagmites. The powder is mixed with a monomer solution, which forms a clear gel. The gel was applied as described and allowed to harden into clear acrylic.
This is the same stuff use in nail salons to work on acrylic fingernails. It makes your work area smell like a salon for a while, but its great for ice effects.