Measurements have been made of the magneto-optical rotation at visible wavelengths of the following optical materials: Dynasil 1001 fused silica, Schott BK-7 borosilicate glass and undoped YAG crystal. A pulsed magnetic field of about 7.0 T was used. The YAG crystal was shown to be a good alternative material for constructing a visible optical isolator, with a figure of merit M as high as 58.5 rad T-1 at 632.8 nm. From the author's data they calculated the average magneto-optical anomaly factor gamma for each sample, as well as the energy gap Eg and the disorder parameter z by using BHL, KLN and MS formulae. A low value of z was found for the three samples, indicating that the interband transitions involved in the Faraday rotation of these materials are predominantly direct. The authors also calculated the energy gap of their samples through the use of their respective optical dispersion data. Good agreement between the values of Eg calculated by the different methods is observed.