The most effective method is burning the lens with a lighter. However, if the lens is plastic or has some sort of special coating, which a very few masks do, you might better check with the manufacture for their recomendation.
I too have burned every mask I have owned that I can recall. After you give up on toothpaste and magic potions and the mask still fogs, burn the inside with a BIC lighter. If you look close you can see the silicone and other contaminates burn off. Then, after the lens cools, wash it in hot water with plain DAWN dish soap.
Apply anti fog agents afterwards as usual each dive.
N
I too have burned every mask I have owned that I can recall. After you give up on toothpaste and magic potions and the mask still fogs, burn the inside with a BIC lighter. If you look close you can see the silicone and other contaminates burn off. Then, after the lens cools, wash it in hot water with plain DAWN dish soap.
Apply anti fog agents afterwards as usual each dive.
N