currently except for the new epson 2200, all the black inks available are dark gray. so u lose contrast. and the paper is not really white, but light yellow or light grey.
plain paper absorbs the ink into the paper, hence u lose more contrast and it looks well, paperish...
so u get about 70% of the contrast, and 50% brightness.
photo paper or coated have the sticky acrylic surface to prevent the paper from eating the, and to supply a high reflective index so that the white is bright enough. so u get about 85% of the contrast, and 70% of the brightness...
the epson 2200 uses a matt black ink that is non reflective (I suspect scratchable) so it's 80+% contrast and 85% brightness.
u want 95+% brightness use a lightbox and transparencies. LOL