A control system for a hydraulic servomotor is disclosed. A worm gear is attached to a motor shaft of the motor. 5% of sulfur present as non-sulfuric acid form sulfur andor has a concentration of non-sulfuric acid form sulfur to elute, of at least 100 mgl, and further, preferably, has a degree of vitrification of at most 30%, a melilite lattice constant a of from 7. Leverage relating to the ratio of the collateral value and the exposure can be managed to offset the exposure.