Matte or Gloss - A Cautionary Tale
The users of Epson inkjet printers also know that there are two black inks in their machines ;Photo Black and Matte Black. The 3800, 3880, 3000, SC-600, SC-800 and so on all have these choices - based upon the fact that you might be putting matte paper or gloss paper through the thing.
Some of them switch themselves from one choice to the other automatically when your computer sends the printing command - it contains a specification about what you are doing. Some need to be switched with a series of on-machine commands. The procedure is about the same in both cases. The printer shuts off one ink pipe and then flushes through the head with a little of the other sort. When it is ready to go it signals you or just whooshes on with the job. Very civilised.
If, like me, you concentrate most of your printing on one sort of paper - in my case smooth pearl surface - you may use only one sort of black ink for months at a tme. While everything else gets stirred up all the time and flows nicely the unused ink in the other black cartridge settles and ages...and can clog up the heads when you try to switch to it.
Look at the cartridge that you don't use - or at least keep a record of when it went into the printer and what the expiry date was on it. If it is likely to have clagged up in the interim, pluck it out and plug in a fresh one. The price you pay for a new cartridge is a bargain compared to a clogged head and hours spent running cleaning programs.