The biomachining process of OFC samples is shown in Fig. 3, along with the reactions that characterize the chemical behavior (Istiyanto et al., 2010) and a microscopic observation of A.F. Having a part of OFC in a bacterial medium, which has to contain divalent iron (Fe2þ), the bacteria trap the Fe2þ cation from the medium and through an internal catalytic process, cause it lose an electron, thus becoming Fe3þ.