Chinagraph are a waterproof, permanent pencil especially noted for being able mark difficult surfaces such as glass, metal and plastics. Although waterproof it can be removed by using a solvent.
For more info see the Staedtler Website.
Blue Chinagraph Pencils
$2.60 – $22.50
Blue Chinagraph Pencils, now called Lumocolour Glasochrom, are a permanent waterproof pencil that writes on many difficult surfaces such as glass, metal, plastics, paper, wood, leather and stone. Will show up on dark surfaces such as x-rays and black plastic pots.