The Collaborative International Dictionary of English v.0.48:

Atramentarious \At`ra*men*ta"ri*ous\, a. [Cf. F. atramentaire.
   See Atramentaceous.]
   Like ink; suitable for making ink. Sulphate of iron
   (copperas, green vitriol) is called atramentarious, as being
   used in making ink.
   [1913 Webster]