I am well aware that professional sculptors will not be interested. They use hard and noble materials like stone, hard wood, bronze, … . But I think now on sculptors, who lost part of their craft by a handicap. I can imagine that they still “see” what they want to sculpture but have not the force anymore.
In that case, cellular glass could be an option. It is easy to shape with simple tools. It is possible to start from a large block by gluing with for example bituminous or polyurethane adhesive. Errors can be easily corrected with the same technique.
After shaping, the sculpture can be finished with a rendering product, suited for cellular glass. A further marble look is even possible with an extra layer marmolux on this rendering.
10 years ago, I made a 1m high lighthouse for a friend lighthouse collector. The cellular glass was finished with UNILIT 65 from Telling, UK. The typical color was given with a lime paint. The structure was glued with UNILIT K on a concrete block to give it stability against wind. Like today confirmed, after having being outside for 10 years in the Belgian climate with rain, sun, snow and frost, the “sculpture” is still in good shape and will be perfect after the yearly cleaning.
And the price (200€/m³) is also interesting compared with granite, which is of the order of 4000€/m³. Maybe, cellular glass can be used as a “test” before expensive granite is used.