Look at these photos i clicked. This is not dirty as i have cleaned it several times.
https://plus.google.com/photos/110902280530242464807/albums/6106469438386439969?authkey=CI7TlJ_WxdW2Jg
https://plus.google.com/photos/110902280530242464807/albums/6106469438386439969?authkey=CI7TlJ_WxdW2Jg