I know it's embarrassing to ask this question here, but seems no one can answer my question in my home town.
I bought a black sunglass at local optician few months ago. The sunglasses is made of acetate (kind of plastic, the salesman told me) material. After I wore it for around two weeks, the frame was gradually covered by a blue-like coat of dirt. It felt a bit sticky. Therefore, I brought it back to the eyewear shop and asked the causes. Of course, I wanted to exchange a new one, but the salesman just wiped it out and told me "It is normal, no need to worry!" I could feel that he didn't want to exchange a new one and tried to shirk responsibility.
The problem comes to the sunglasses again recently, and I try to reach other opticians and ask them the true cause of the covering dirt. I think if I know the true reasons that producing this sticky dirt on my sunglasses, I may have the power to ask the optician to exchange a new one for me!!
Does anyone know what is the blue-like coat of dirt covering on my sunglasses? And what is the true cause?