Originally Posted by
cyccommute
Aluminum oxidation products, for example, are extremely hard and many even be nonporous. Think anodized aluminum. The aluminum oxide is also much harder than the underlying metal so it doesn't break and slide as easily.
Agree. A class of Al2O3 is called corundum. And beryls, rubies, and sapphires are all in the corundum class. Also, the grit on most sandpaper is corundum.
BTW, in at least one test (and I don't think its apochryfal), a 50:50 mix of ATF and acetone worked better than any pre-made product. But the acetone will strip your paint. I think a product called Kroil was the best commercial penetrating oil.