Sources of Zinc
Zinc is an additive metal found in all anti-wear (AW) additive packages. Only when the zinc level deviates more than 25% from the new oil or reference value should a concern be raised, but the likeliest cause is mixing or topping off with a different product. The zinc level in AW oils is always comparable to the level of phosphorus.
With normal and expected additive depletion due to usage, the additives are still present in the fluid, and will still be measured at their normal levels. Once they do not appear in the fluid, they have dropped out completely, which indicates a more severe degradation mechanism or additive drop-out.
Zinc may appear as wear, but generally, any application where it may exist as a wear metal will employ an AW oil. Therefore, the zinc content would be masked by the presence of the additive. Brass wear can be differentiated from bronze wear, as only brass contains zinc, and both contain copper, lead, and tin. Solders contain zinc, as well as lead and tin; galvanized steel (from piping or tanks) contains iron and zinc; and some coating contain zinc, as well as chromium and nickel.
Watch for the next article in the Elemental Spectroscopy blog series: Barium
