In order to perform SEOP, it is first necessary to prepare the optical cell. Optical cells (Figure 5) are designed for the particular system in mind and glass blown using a transparent material, typically pyrex glass (borosilicate). This cell must then be cleaned to eliminate all contaminants, particularly paramagnetic materials which decrease polarization and the T 1. The inner surface of the cell is then coated to (a) serve as a protective layer for the glass in order to lessen the chance of corrosion by the alkali metal, and (b) minimize depolarization caused by the collisions of polarized gas molecules with the walls of the cell. Decreasing wall relaxation leads to longer and higher polarization of the noble gas.