Epson Stylus Pro 7700 Series Reference Manual page 21

Epson UltraChrome VM Ink Technology
Dual Black Ink Modes – Photo and Matte Black Inks
Two different black ink technologies are automatically used to optimize the black
density and line-sharpness for virtually any media type
Photo Black ink can produce professional results on any media type, but is optimized
for traditional higher-end ink jet papers
Matte Black ink can produce even better results on standard plain and tracing papers
Matte Black Print on Matte Paper Photo Black Print on Matte Paper
Photograph © 2010 Lois Greenfield