If two metals both have the same color, have similar densities, and are about the same size, but one is shiny and the other is dull, they can be separated based on the physical property known as what?

If two metals both have the same color, have similar densities, and are about the same size, but one is shiny and the other is dull, they can be separated based on the lustrous physical property of a metal. Lustrous is the property of the metal to shine/gleam gently because of its particle arrangement of atoms. 

Solubility would be your answer.