It looks to me like a soiled bottom plate.
Here's what I would do if it were mine...
- Find an old dinner plate or similar
- Fold a paper towel into quarters and place it on the plate.
- Thoroughly moisten the paper towel but don't create a puddle. Distilled water is best, tap is OK if no distilled on hand.
- Open the printer as if to service a cartridge. When the carriage moves to center and stops, unplug the printer.
- Remove the printhead/cartridge assembly...leave the carts in place.
- Do not touch any of the electrical contacts, do not wet the electrical contacts.
- Inspect the bottom of the printhead, I'm thinking that you will see some black ink (paper fibers) that is fouling the black nozzle area ?
- Now, take the printhead assembly and gently blot it on the waiting paper towel sort of like a rubber stamp, but go lightly. Don't rub.
The black nozzle area will probably put down a large undefined black mark at first.
After several blottings you should start seeing a "regular" pattern of all your colors.
When you are satisfied that the bottom of the head is clean, replace it.
- Print a test pattern, if necessary perform a standard nozzle cleaning.
- If everything seems OK, perform a printhead alignment and then go printing.
The large black tank in your printer is supposed to have pigment-based black ink in it. It is used for text-only printing to provide sharp, durable text.
All your other tanks are dye-based inks.
Some of the aftermarket ink companies have trouble duplicating the Canon black pigment ink which can cause various degrees of trouble for the printhead.
Keep an eye on it.
Also clean the printhead wipers with Q-Tips moistened with Windex. One is left and one is right near the Park Pad. You also may want to clean the park pad by carefully syringing some Windex onto it. Do these steps before powering up the printer and the carriage is still at center.