I was rereading the runes for vitkir and found this entry in the Othila rune (p. 134).
Ok, how do you interpret this? It is a guideline. I have not found what "exceptional quality" means outside this boxed text since C&G has superior and excellent items (and wondrous items) but not exceptional quality items.
Is the botch reduction the meaning of "exceptional quality"?
If not, what does it mean for you? Would that be another name for superior or excellent quality?
I would say the exceptional quality is the botch reduction bonus. No amount of super crafting by an excellent artisan using the City & Guilds rules can give you an item that reduces botch dice. So no, it won't give you any of the other bonuses that well-crafted items do just by crafting a rune on it, but I would say it will stack with other bonuses, so if your vitkir buys a superior dagger from a great craftsman (C&G), purchases some alchemical preparation to strengthen it (A&A) he can then carve an Othila rune on it to add yet another category of bonus.
I think that Superior items could also be reflected by reducing botch dice by 1, to represent an item that is well-balanced and sturdier and a standard item. That would replace the usual +1 bonus to a specific activity, not in addition to it.
The real question is how one could use this base effect to reduce botch dice for spellcasting; can you target your writing implement or the material it's being written on, or do you need to make yourself a instrument of Exceptional Quality?
A far easier way of doing that is to use Pertho to reduce botch dice. Pertho itself is associated with the realm of Magic and the form of Vim, so you can use Pertho for a runemaster to reduce their own botch dice with regards to magic.
Such a spell is in Diserasta's post on page 7 of the "non-hermetic grimoire" thread.