I am a BIT embarrassed to be making this post as I suspect the information I am looking for will turn out to be obvious.

I have just set up my Canon PIXMA ip4500 and it WORKS fine, however I have not managed to find any info in the help manuals to tell me why I have two black ink cartridges, nor to tell me how to use one rather than the other. Can ANYONE ADVISE?Quote extracted from here..

Quote

The ink mix benefits output quality. Dye-based cyan, magenta, yellow, and black offer a broad palette; a second, pigment-based black looks darker and lasts longer. Each ink's separate tank rests in a clearly visible slot above a permanent printhead. As other Canon printers have had for a while, an LED on the cartridge lights red when it's properly inserted--an odd color for affirmative feedback, but still informative. The Pixma iP4500's dye-based black costs 3.1 CENTS per page; a page with cyan, magenta, and yellow as well costs 8.4 cents. The pigment-based black, used only for plain text, lasts 5475 pages, or just a fraction of a penny per page.