…is the use of 7 shades of black/gray ink to create an image you feel you can reach into.
Instead of creating shades by dithering (interweaving) two or three shades of black, as most printers do, the use of 7 shades with overlapping curves (and no dithering) yields a museum-quality image, which is often mistaken for a silver print.
I have dedicated an Epson 3880 to just that technique.
Images of such quality really need to be on the highest quality paper. The choice of paper, warm or cool, goes a long way to the subjective impact of your print, and should therefore be carefully selected. Although I use a variety of papers, I generally prefer Canson Infinity Arches Velin Museum Rag.
You can find out more about this fine art technique at www.piezography.com .