So I am a bit... dissatisfied with how runes are described, they are so close to many familiar mechanics but a lot of oddities like runestones and somehow removing a carving from a surface to move it to another keep it iffy. To remedy this I've built a small collection of house rules that help remedy the issue. It is built around Automatic Bonus Progression since that's a system I always use, now without further adieu:
Runes are now "X Crystals" enchanted gems similer in appearance to an Ioun stones, they require magical Crafting to make and can accept any one gem or crystal as material to cover crafting costs. Unlike runes these crystals can always exist independently of items and runestones do not exist. Crystals have a Bulk of L.
Crystals can be affixed to items that have specially made slots for them. Affixing a crystal always has the 10% crafting cost to represent applying fastening (usually a small amount of gold silver or mithril) to hold the crystal in place and intigrate its effects. Applying a crystal requires the magical crafting feat, however removal can be attempted without it. To remove a crystal without magical crafting requires a craft check with 15+the crystals level as the DC.
Critical success: you remove the crystal without issue
Success: you remove the crystal but damage the item in the process giving it the broken condition.
Failure: you fail to remove the crystal and damage both it, and the item. Both items become broken
Critical Failure: you fail to remove the crystal and destroy it, as well as damaging the item it is affixed to.
This brings us to slots, Items have a number of slots depending on the skill of the craftsman as follows.
An Expert skilled craftsmen can create an item with 1 slot, this adds 10 G to the base price of the object and makes it a level 2 item.
A Masterfully skilled craftsmen can create an item with 2 slots, this adds 250 to the price of the item and makes it a level 7 item.
And a Legendarily skilled craftsmen can create an item with 3 slots. This adds 2500 G to the cost and makes it a level 15 item.
This system of Expertly made, Masterwork and Legendary items replaces the Grade system for items, and all special matireal items use the price modifiers in the matireal section rather than the specific price for a given armor/shield/weapon of that material.
Ergo an expert craftsman can make items of cold iron and silver with a cost of 10+ item cost + 20 per bulk.
Wheras it takes a Legendary craftsman to work oricalcum with a cost of 2500 +item cost + 10000 per bulk.
When an item with Crystals slotted into it is damaged the Crystals are safe, however if the item is destroyed all Slotted Crystals become broken.
I'm certain I have forgotten bits but that is largely the guts of it.