Sorry, a Google search got results.. Here is what I found.
It is calc-spar, in a setting of heavy-spar or sulphate of baryta. 1885 Encycl. Brit. XIX. 86/2 Baryta White..is prepared by grinding to a fine powder the pure white native sulphate of baryta (heavy spar).
Baryta fills in paper for opacity and aids in maintaining paper flatness.
Unprepared photographic paper implies un-sensitized paper; but must relate to the application of the baryta.
Last edited by Richard Jepsen; 09-23-2011 at 10:10 PM. Click to view previous post history.