Here is the titration curve for the ink base. It's surprisingly simple to me and it appears there is only one acid-base active component. I quick look at Epson's MSDS for inks shows that 5-10% is an organic component, 10-20% is glycerols and the balance is ink and water. IF anyone wants more data from this let me know and I'll see what I can do.

With the thoughts from Caltech, I believe we are dealing with a cationic surfactant in aqueous propylene glycol. After quick look at cationic surfactants, it's possible we have an alkyl(dimethyl)amine, which is protonated to the ammonium salt when we acidify it. My think is that this is good for us as it should not complex or interfere with the metal ions in this form. It might also explain the problems with straight ink base as the amine could complex to the metal ions making a mess.

Cheers,
Casey-Oswego