Worn, damaged arms & armour
Bashed, dented, busted & rusty arms & armour.
I like a lot of the knight series but yes the lords & nobles have squires & servants to do the polishing and mending but the lesser men at arms often had to make do a bit rougher.
Example: professional knights who took to the field for pay & loot (and killed other knights for a living) often had their armour pitched (black knight) was of course infamous as a result.
Not all knights where kitted out like prince charming and after a long a campaign even the best off would look a bit scruffy & dented.

Comments
I think your best bet it to apply an overlay to the armor / weapon.
Could either be in the overlay channel, or on a geoshell. You could add a mask to the areas where you want it, but that would require that you do it.