transmutation 

Traditions arcane, occult

Cast [>>] somatic, verbal

Range touch; Targets 1 weapon that is either unattended or wielded by you or a willing ally

Duration 5 minutes

The target weapon becomes translucent and ghostly, and it can affect material and incorporeal creatures and objects. It can be wielded by a corporeal or incorporeal creature and gains the effects of the ghost touch property rune.

If the weapon is magical and already has the maximum number of property runes, the wielder can choose one to suppress to gain ghost touch.

Core Rulebook, page 340.