Gold only use is for corrotion prevention, it has no industrial use. Silver by the other hand has a lot of usage, includin gun powder manufacturing. If aluminum and iron where securities i would make money of it. Iron is almost low cost, when it rallies it stays there for a while and then it plummets. Aluminum is the most common metal on earth but ironicaly is the most expensive to produce, it is cheaper to recycle it but the already produced aluminium is very expensive. Copper, i think is the true security as long electricity is still in fashion, because is the best electricity conductor and is not an easy element to harvest. Titanium i think it has a potencial because it is cheapper than aluminium and more resistant. Finally magnesium, it can be used for fireworks, cars and now laptops, why? because it dispates heat better than steel and aluminium. So if you are going to trade with metals this is the information you need to handle.