Explosive Runes on a weapon?

[Barstro]

I was thinking about only making available on hammers. In the portion of the head that strikes the opponent. Useful in combat and breaking things like a boss.

RAW, it has to be read. But, nothing says the writing has to be all that verbose. Maybe the runes can spell "HI".

The object on which the runes were written also takes full damage (no saving throw)

I'm not versed in damaging objects. RAW, the hammer gets damaged. Also RAW, writing it on a piece of paper and sticking it to the hammer does not result in damage the hammer at all.

Interestingly, I see nothing to suggest that your "target" needs to do the reading.

1) You trace these mystic runes upon a book, map, scroll, or similar object bearing written information.
That seems to exclude "hammer", but include "paper attached to hammer".

2) The runes detonate when read,
Spell is silent as to who gets to read it. Maybe someone with good vision from across the room gets to read it.

3) Anyone next to the runes (close enough to read them) takes the full damage with no saving throw;
I assume "anyone" means "creature". I assume "next to" means "melee range" (5 feet).

4) any other creature within 10 feet of the runes is entitled to a Reflex save for half damage.
Gives credence to "5 feet".

5)The object on which the runes were written also takes full damage (no saving throw).
But not an object attached to that object. Which means my thought experiment of attaching rune-paper to mountains in order to dig tunnels is not going to work.

6) You and any characters you specifically instruct can read the protected writing without triggering the runes.
"Can", not "shall" or "must". The wielder can trigger the runes.

But, I cannot find a way to make the wielder immune to force.

Intelligent returning hammer that can read the rune paper that's stuck to it?