When capsules of compressed hBN powder were used, rs-ZnO was also observed in recovered samples after triaxial compression, but only as a by-product (~8 vol.%). In the case of uniaxial compression, the amount of rs-ZnO in the recovered products decreases from ~25 vol.% in the case of pyrolytic BN capsules to ~9 vol.% for capsules of compressed hBN powder. In the absence of a BN environment, both types of compression lead to pure w-ZnO phase: nanostructured in the case of toroid-type apparatus and microcrystalline in the case of multianvil device.