Preparation of samples with a mirror-like finished surface requires several previous steps. First of all it is necessary to carry out a lapping process on the surface in order to decrease the high roughness in the as-cut samples. Fig. 1 shows the most relevant results for a sample which was submitted to a lapping process according to the type and particle size of the abrasive used. The first selection is to choose the optimal type of abrasive and particle size according to the roughness results. Al2O3 was selected due to the lower roughness value, consequence of the lower hardness value of 9 compared with the higher value of SiC of 9–10 [12]. In the same figure it can be seen that when Al2O3 abrasive is used for similar experimental time, the roughness value is reduced for smaller particles size. Therefore, considering that for both 3 and 1 µm Al2O3 the smoothness was similar given by the optical microscope and taking into account that the process with 3 µm Al2O3 is shorter compared with the process with 1 µm Al2O3, we select for next experiments 3 µm Al2O3 abrasive as the unique lapping step.