Heat sink surface Treatment
Aluminum heat sinks are usually anodized; a choice of many colors is available. One might think that black is good, because it is best hat emission by radiation. This is wrong. Heat sinks get rid of heat by convection (that is, heat is transferred to the air molecules travelling along the heat sink surface – if a fan is involved, we call it “forced convection”) For convection, the color does not matter at all.
Copper heat sinks are sometimes plated with or even gold. This is supposed to prevent corrosion and improve thermal characteristics. But actually, the plating is too thin to have any effect on thermal conductivity. It is true that the surface of a copper heat sink may slightly corrode; but since they are operating in a dry environment, and do not have to withstand extreme temperatures, corrosion is not really a problem. During the lifetime of a PC heat sink, the corrosion layer will not get thick enough to have any negative effect on cooling.