Earlier today I found a Quartz Cuirass which is a Glass Cuirass enchanted with 15% resist normal weapons. If I have an AR of 85 while wearing the quartz cuirass will I effectively be immune to normal weapons, will the 15% be taken off of the damage first with the AR applied to what's left, or will the AR be applied first with the 15% be applied to what's left?

I rarely bother with any Resist Normal Weapon enchanted item. Because at later levels enchanted or silver or Daedric weapons are so common it's not worth it.

But Resist Normal Weapons does not increase your armor rating, and is calculated separately.

So if you have 85 armor rating and 15 resist normal weapons and are hit with a normal weapon with 30 points damage then

The armor rating will reduce the damage to 4.5 point. The resist normal weapons will reduce it further to 3.825 points of damage.

Thanks for the reply, looks like I'll be sticking with my old cuirass.