Well, since it's here I'll drop a couple of comments.

When you blow into a cartridge you impart moisture on the contacts. And it's not moisture from your breath. Because the steam from your breath will evaporate within a couple of seconds. When you blow on a cartridge, with that expelled carbon dioxide there is small amount of saliva. Saliva contains a lot of bacteria, minerals, and is also a mild solvent. It is not something you want sitting on electrical contacts, or any part of an electronic device for that matter. It will slowly eat at the electrical contacts through corrosion.

Oh, and patina is just a fancy word for corrosion.