Castagnacci's abstract work in painting, printmaking and drawing has been centered in the principle of variational development. His work articulates a personal geometry and communicates a strong sense for tectonic values.

Castagnacci has received numerous grants and fellowships from Michigan and most recently was a Mellon Scholar at Kalamazoo College. In 1980 he was awarded a Citation and Grant from the American Academy in Rome where he was visiting artist for nine months. In 1999 he was named Arthur F. Thurnau Distinguished Professor of Fine Arts. He has lectured and published consistently in this country, in Rome at L’Istituto Nazionale per la Grafica and at the Gebaudelehre, Technische Universitat in Vienna.

In 2022, the Cape Ann Museum in Gloucester MA presented a special exhibition of works by the artist titled Notes from a Quarry.