[stomachmonkey]

Different manufacturers use different approaches.

Some HP ink has a "shelf life". Beyond a certain date it prints like garbage regardless of how full or used it is.

Epson are the worst, their chips "estimate" how much ink is left so you could be tossing a cartridge that still has 20-30% life because the chip has "determined" it is empty.
Once the chip does that the cartridge is unuseable.

To refill this type on your own you can get a deveice off the net for like $5 that will reset the chip.

It's a total scam.

I have 3 stores locally that will refill my $30 HP plotter cartridges for $8 each.