Synthetic guanine crystals, with the same magnetic controllable reflection property as a biogenic guanine crystal from fish scales, were prepared using a classical Ostwald ripening method for crude crystals, from the aqueous sodium hydroxide solution of a commercially available synthesized guanine powder. The resulting synthetic guanine crystals with an average size of several tens of micrometers were in the same crystal system as the biogenic guanine crystals under measurement by X-ray diffraction (XRD). However, XRD patterns of water-floating crystals showed that the correlation between the growing direction and reflecting surface in the synthetic crystals is different from that in the biogenic crystals. Therefore, the synthetic crystals were ground by an agate mortar for refinement of its optical and magnetic-orientation characters. As a result, we realized a fast-magnetic orientation against the vertical field, which is related to the magnetic control of light reflection, the same as the biogenic guanine crystal behavior.
