Blackdirt or soot, especially such dirt clinging to or ingrained in a surface.
污垢，灰垢黑色脏物或煤灰，尤指附着或深嵌在一个表面上的污垢。
2
They were all covered in black soot and dirt.
他们都包括在黑色烟尘和灰尘。
3
If you haven't seen these nymphs before on the site, they're actually jet black: the white coating is lint and dirt that they glue to themselves with spittle to form camouflage.