Single crystals of cuprous oxide (Cu2O) with minimal defects were grown using the optical floating zone technique. Copper vacancies were removed through the promotion of CuO precipitation within the bulk Cu 2O crystal following the reaction CuCuCu2O + VCuCu2O + OOCu2O → Cu CuCuO + OOCuO. This reaction was promoted through the use of high purity samples and by growing crystals under an oxidizing atmosphere. Although an increase in the oxygen concentration of the atmosphere will initially increase the oxygen to copper ratio, the excess oxygen in the final Cu2O crystal is ultimately decreased through the formation of CuO as the crystal cools. Copper vacancies were reduced further, and the CuO phase was eventually removed from the Cu2O crystal when thin slices of the crystal were annealed.