Do inkjet printers use color ink when printing black and white documents? If so, why?

Yes, many inkjet printers use color ink even when printing black and white documents, although the amount used is typically small. Here are the reasons for this:

Print Quality Enhancement

Inkjet printers often use a combination of black and color inks to improve the quality and permanence of black text and graphics. This is achieved through chemical interactions that enhance the blacks on the page, resulting in smoother gray tones and better overall print quality25.

Print Head Maintenance

Epson and other printers use a small amount of color ink to keep the print head charged and prevent air bubbles from entering the print head, which could damage it. Even when printing only black text, the printer needs all colors to maintain the health of the print head4.

Composite Black

For black and white images or photos, some inkjet printers use a blend of colors known as "composite black" to achieve better image quality and smoother gray tones than what can be accomplished with black ink alone2.

In summary, while the primary ink used for black and white printing is the black ink, many inkjet printers will still utilize small amounts of color ink to maintain print head health and enhance print quality. If you need to avoid using color ink entirely, a monochrome laser printer would be a better option15.