The most recent direct filling gold which produces the hardest surface on condensation is: (A) Mat gold, (B) Encapsulated powered gold, (C) Mat gold alloyed with calcium and wrapped in gold foil, (D) Platinized gold
Answer is C. Mat gold made of electrolytic precipitate from gold, which is alloyed with a trace amount of calcium, can yield a further increase in hardness by dispersion strengthening without affecting the handling properties.