I'm looking for a YA fantasy-book. I think it's the first in a series.
It's set at a magical school, where new students start in their teens (I think around 18). New students are taken to a cave, here they go through/dunk in (naked?) a pool of water. Afterwards, tattoos may become visible on certain places of their bodies - each corresponding to an ability... and often "paired" with the opposite ability (eg. fire and water) on the opposite part (eg. left and right upper arms). Each student get one or more tattoos, which determine which abilities they may study/train in, and classes to take. More tattoos - and thus more abilities - are desired. An old book lists the tattoos and abilities. I believe there are around 10-13 different tattoos/abilities, though one has never been seen and is believed to be mythical.
The main character - a girl - and her best friend (also a girl), joins the school together. The friend only gets two or three tattoos and is bummed because of that. The main character, of course gets all of the tattoos - including the one never before seen.
With so many tattoos, the girl gets a grueling schedule. Among her tutors is a young boy she falls for.
Does this sound familiar?