As far as I can tell the hardened teeth are hardened after sharpening as the tarnish is only surface staining that wears away, so it must be that they are just as sharp as other saws when first sharpened. Most people (including my father) never did enough woodwork to warrent sharpening, so I neverknew of it. My sharpening insight with regards totools comes from my now passed on uncle, carpenter 50 years. Brace and bits chisels saws, but even he rated the hardpoints, probably as they kept sharp so much longer. If you use a very hard file to sharpen they will sharpen the hard point teeth, but the old softer saw tooth files will just blunt themselves. Any idea how to to reharden the teeth?