The makeup detector

I usually didn't take much/any notice of makeup that people wear until once i went to meet an acquaintance near their hostel. This person was waiting outside the hostel gate. I arrived on time and began carefully looking around for the acquaintance, only in vain. Eventually, this person walks to me and says 'hi'. It was only then i realized that the person had worn no make up at all. It then made me realize, how a 'make up' can result in a 'make over'. Nevertheless, from that day on, i was keen on trying to detect how much make up a person really wears.
Initially i noticed that many folks wearing make up had a different skin tone at the back of their neck with respect to their face. The funny thing is that the mirror will only reflect the face and not the back part of the neck and its easy to forget the contrast. The same applies for hands and feet. All you need is to compare it with the face. This makes it easy to detect the variations and is probably a good way of getting a real idea of the actual tone of the skin.

Naturally folks get smarter and touch up the neck,hand and (maybe even?) feet and makes it nearly impossible to compare. However, all is not lost. We have optics to the rescue :-) It has been found that when light falls on a translucent object (like the skin), it actually goes into the skin and reflects back making the skin appear smoother while make up actually causes light to reflect directly making the skin loose its translucence.

A good approximation of the face with and without makeup is visible in this article on page 54, Fig 32. Other than the skin tone, the difference in the shadows under the nose is clearly visible.

Infact, I came to know about this during a talk on computation cameras at a symposium. I guess i am able to put to good use some of the info :-)