A masterwork weapon is a finely crafted version of a normal weapon. Wielding it provides a +1 enhancement bonus on attack rolls.
You can’t add the masterwork quality to a weapon after it is created; it must be crafted as a masterwork weapon (see the Craft skill). The masterwork quality adds 300 gp to the cost of a normal weapon (or 6 gp to the cost of a single unit of ammunition). Adding the masterwork quality to a double weapon costs twice the normal increase (+600 gp).
Masterwork ammunition is damaged (effectively destroyed) when used. The enhancement bonus of masterwork ammunition does not stack with any enhancement bonus of the projectile weapon firing it.
All magic weapons are automatically considered to be of masterwork quality. The enhancement bonus granted by the masterwork quality doesn’t stack with the enhancement bonus provided by the weapon’s magic.
Even though some types of armor and shields can be used as weapons, you can’t create a masterwork version of such an item that confers an enhancement bonus on attack rolls. Instead, masterwork armor and shields have lessened armor check penalties.
Just as with weapons, you can purchase or Craft masterwork versions of armor or shields. Such a well-made item functions like the normal version, except that its armor check penalty is lessened by 1.
A masterwork suit of armor or shield costs an extra 150 gp over and above the normal cost for that type of armor or shield.
The masterwork quality of a suit of armor or shield never provides a bonus on attack or damage rolls, even if the armor or shield is used as a weapon.
All magic armors and shields are automatically considered to be of masterwork quality.
You can’t add the masterwork quality to armor or a shield after it is created; it must be crafted as a masterwork item.