This caps at the exact level regular ash lumber does. All the magical items cap at the same level as their non-magical counterpart. The only difference is that one needs the purification/enscrollment Key Item to make them.
I was just using up some wind crystals and was given this recipe at Lv.2 Woodworking skill. I'm betting it is a Lv.8 skill cap also. It is Ash Lumber afterall which caps at 8. Key item Wood Purification needed as well.
Yea, Ash Log, Ice Anima, Earth Anima, and Light Anima I got if from mysterytour ^^ --I still go here but mysterytour always has stuff up first, and always accurate, and correct recipies