A method of growing monocrystalline bismuth rare earth iron garnet, either as a single crystal or as an epitaxial layer, from a solution containing composing components of the garnet together with a flux. The flux consists essentially of a mixture of Bi.sub.2 O.sub.3 and RO.sub.2, wherein R is at least one of the elements Si, Ge, Ti, Sn, Zr, Ce and Te, wherein the system Bi.sub.2 O.sub.3 --RO.sub.2 includes a eutectic composition having a eutectic temperature which is below the melting temperature of pure Bi.sub.2 O.sub.3. By using these Bi.sub.2 O.sub.3 --RO.sub.2 fluxes, the monocrystalline garnets produced have lower optical absorption coefficients at, for example 5100 A and 5600 A than similar garnets grown using lead-containing fluxes. Furthermore higher growth rates and higher growth temperatures are possible when using the Bi.sub.2 O.sub.3 --RO.sub.2 fluxes rather than lead-containing fluxes.