The Collaborative International Dictionary of English v.0.48:

Lampblack \Lamp"black`\, n. [Lamp + black.]
   The fine impalpable soot obtained from the smoke of
   carbonaceous substances which have been only partly burnt, as
   in the flame of a smoking lamp. It consists of finely divided
   carbon, with sometimes a very small proportion of various
   impurities. It is used as an ingredient of printers' ink, and
   various black pigments and cements.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lampblack
    n 1: a black colloidal substance consisting wholly or
         principally of amorphous carbon and used to make pigments
         and ink [syn: carbon black, lampblack, soot, smut,
         crock]