A 30 year old male patient complains of food lodgment and pain in lower right back teeth region. RCT was done with 46 and 45 was missing. Cast metal restoration with gold alloy was planned for 46. The patient is not happy with the color of the prosthesis. The reasons for the color of the prosthesis may be all except:

Surface discoloration and roughness can result from sulfur contamination. This effect may be seen either from investment breakdown at elevated temperatures or from a high sulfur content of the torch flame. The interaction of the molten alloy with sulfur produces a black or gray layer on the surface of gold alloys that is brittle and does not clean readily during pickling. Philips’ Dental Material, pg- 224