How can I identify corrosion products of steel using simple process?

As I am doing a research regarding corrosion, I immersed a steel in a salt solution. Different colors of corrosion products were produced as time passed. There are blackish, the usual red-brownish, and others. But, I need to identify if it is really corrosion products or the iron oxide to confirm that they are not just contaminants. What is the simplest way possible?


