Arcane Whetstone

This otherwise mundane whetstone shimmers with magical energy when it is charged.  The Arcane Whetstone holds a charge indefinitely at the expense of one spell slot (or by ritual if the caster has the Ritual Caster feat) and 10 minutes.  When charged, the first weapon sharpened on the stone absorbs this magical energy and gains the benefits of a modified magic weapon spell for six hours without concentration.  

The weapon gains this benefit by physical sharpening, thus the spell only applies to bladed weapons that can be sharpened on a whetstone.  The whetstone only holds one charge at a time which is expended on first use.

Magic Weapon. You sharpen a weapon. Until the spell ends, that weapon becomes a magic weapon with a +1 bonus to attack rolls and damage rolls.

This buff stacks with existing buffs to hit.