Raising attributes beyond 15?

This is probably a real noobish and easily answered question, but how do I raise an attribute above 15?

I'm trying to get my Expertise up just one more point, but Runes and the +1 bonus from Rangers' masks don't stack. I just need to get to 16 in order for my build to work. Someone help please!

Posted here instead of the Ranger build specific forum because it seemed like more of a general 'how to do this' question.

They do stack.

12 attribute points, +3 from superior rune, +1 from headgear = 16 expertise.

put 12 into expertise,get a +1 expertise helm,put a sup expertise rune on it

I've got a Canthan Mask I bought at Kaineg Center and it doesn't stack. Do you happen to know where I can get a max armor mask that has a stacking bonus to Expertise?

EDIT: I'm a dummy. The reason the bonus doesn't stack is because the mask has a minor rune in it. Graaagh! The question about where to find one that does have a stackable bonus to Expertise could still benefit from an answer.

Any headpiece with an innate Expertise+1 will stack with the rune bonus. Are you sure you didn't buy a headpiece without the +1 (don't know if that's even possible)? Are you trying to put a minor rune and a superior rune onto it?

http://guildwars.wikia.com/wiki/Ranger_Canthan_armor

"*The collector mask does not come with a +1 attribute bonus."

You need to craft one. There are 3 armor crafters in Kaineng Center (possibly some others scattered throughout the city). They offer the same items, just with different looks. Make sure you check which headpiece you get as each seems to be the same except for the innate attribute bonus.

Ranger masks with +1 of any ranger attribute can be bought from any armor crafter. The +1 bonuses from the mask are always stackable. If you want 16 in Expertise, for example, you put in 12 from attribute points, plus 1 from an Expertise+1 mask, plus 3 from a Rune of Superior Expertise.

Btw, there are also headpieces available in EotN that give +1 to whatever attribute rune is put on them (so you don't have to buy a specific expertise+1 one.

Thanks for all the responses, guys/gals. I really appreciate you all coming through.

I realize that I was just dumb and purchased a mask without any bonuses (or at least the wrong one) and just need to buy the right one.

I am intrigued by this.

Also: is 16 the absolute highest you can go with gear alone (no blessings/skill/buff effects)?

You are correct the max is 16 and don't forget using a +2 or +3 rune isn't usually advisable due to the health loss.
Most skills improve in power in stages and a skill of 14 ie 12 +1 +1 may give the same effect as 16 ie 12 +3 +1

You can make up some health with Rune and weapon bonuses but I would prefer the highest health I can get

Normally you achieve this through +1 headgear and then a superior rune of whatever. But in PvE you can also gain blessings and consumables that boost your attributes.

I should have linked this before - http://guildwars.wikia.com/wiki/Common_armor