The Collaborative International Dictionary of English v.0.48:

Ivorytype \I"vo*ry*type`\, n. (Photog.)
   A picture produced by superposing a very light print,
   rendered translucent by varnish, and tinted upon the back,
   upon a stronger print, so as to give the effect of a
   photograph in natural colors; -- called also hellenotype.
   --Knight.
   [1913 Webster]