It takes some practice to get the subtle shapes and flow of Quarter Sawn Oak Ray right, but the effort is worth it. 

From Wikipedia: “In botany, Medullary rays…refers to radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings. “

Yikes. So technical. We don’t have to worry too much about that.

In fact, I suggest that you ignore the botany and just focus on how quarter sawn rays look

Perfect Wood Grain Courses include images of realQuarter Sawn Oak. Studying real wood models is the best way to learn to paint faux wood

In Wood Graining, there are lots of tools and shortcuts for creating the various aspects of gorgeous, realistic faux wood.

Unfortunately, Quarter Sawn Oak just takes practice.

Again, the effort will be worth it.