Now that you mention it… The humour in all the wardrobe mirrors in my apartment being black mirrors is not lost on me. 
I will need to take a photo of them to share. They’re actually eerie. 
Especially after a Japanese horror movie marathon for me with my long, dark hair. Between The Ring and The Grudge (Ju-On)… Eek!
[Tenor]
It’s a type of cornmeal, or ground corn kernels, as far as I know.