The art was way too heavy. In mid-March, the artists Holly Herndon and Mat Dryhurst were preparing an installation to coincide with the Venice Biennale, the prestigious international art festival, but the execution was becoming tricky. They wanted to suspend sculptures of a trippy cityscape upside down from the ceiling of an 18th-century palazzo. But the construction material they envisioned—​3-D-printed sand—would weigh tons, which was more than the antique building could bear. The sculptures,