Each cosmetic shape is manipulated with a little grid of red lines connecting different points, and you manipulate the shape by dragging the points around. What I've noticed through my fiddling and experimentation with Blue Mars cosmetics is that the straighter these lines are, especially the vertical lines, the smoother the edges of the shape should appear.
I've tried to illustrate this in the picture to the right (which is a close-up of the two different looks shown in the top image). Note that in the green highlighted image, the vertical lines in the grid are more or less straight, whereas on the red highlighted image they are bent and angular. Even though the eyeshadow shapes are very similar in both, the version with straighter lines does not bleed and smudge out on the avatar's face as much as the version with more angles.
Now it would be a mistake to say that this is the only force at work when you have a smudgy-looking edge on your cosmetic layer: the mesh that makes up you avatar's facial shape also plays a big part. Certain sections of mesh may pull or distort texture applied to them, and if you're familiar with clothing design in Second Life this likely sounds very familiar. Don't be afraid to experiment, you'll find out what works for your face and what doesn't!Do you have any tips or tricks to get perfect looking makeup in Blue Mars? Leave a comment, or email me!