In article ,
"Ed Pawlowski" wrote:

"harry" wrote

You will not get black. That's why there's a separate black cartridge.

It was not always like that. Check out an HP500C printer that had only one
cartridge. It was not a true black, but "close enough" for most people.

It's the difference between theory and practice. Nevertheless, the OP is
trying to forge black from what he has available. Equal proportions are
his best/only option and he gets what he gets.