On Wed, 31 Mar 2004 11:48:03 +0100, in uk.d-i-y Tony Bryer strung together this:
>> Aha, the opening was marked on the underside, and the wandering
>> appeared on top... oops.
>
>Bosch (and presumably others) make downward cutting blades so you
>can safely cut from the top without risk of chipping.
>
Although not really critical for sinks as the edge of the cut is covered by the return edge of the sink. Still a useful blade to have in the collection though.