I've discovered a fabulous way to make eyeliner look natural. You know those highlighter pens, such as YSL, which come with an applicator and brush? Well, what do you do with the applicator when the product runs out?
I use the brush of my applicator to dip into a powder eyeliner (even loose powder brown eyeshadow works) and because the brush of the applicator is already 'soaked' in the highlighter product it easily picks up the powder.
Apply the brown eyeliner in the normal way and you will find the applicator brush gives the smoothest, sexiest finish ever!
Eventually, the brush will start to 'dry out' - but just wash it and try dipping it into normal liquid foundation, wipe some off, and start all over again with the eyeliner thing!