Maker - Alchemy Skill FAQ and Walkthrough

Sorry to "bump" the thread but i have a question about black and dark crystals.

Since maker skill is out in Msea i hope someone will have the answer.

So;

Black crystal (don't care about the grade) is or is NOT able to add -3,-2,-1,0,1,2,3 atk to a weapon?
Dark crystal is or is NOT able to "add" atk to a weapon too?

Or both are just able to "add" STR, INT, DEX and LUK?

Im pretty sure black crystals can add any stat that goes in +2, +3, +5and Dark Crystals can add any stat that goes in +1, +2, +3.

Could be wrong though. I don't see why they would subtract stats though, that seems stupid.

Then again