Have you thought of lapping the flat faces? I've had a really good finish on all types of ferous metals using diamond lapping compond. Hyprez and Engis supply it in water or oil soluable form. Actualy I think on of those companies have gone bust, but cant remember which. Lapping also gives a really flat surface. I beleive they'll lap samples free of charge, but doubt they'd do both faces f a "sample"