Also, if you've formulated your own ink, with conducting additives, then you've likely changed its properties, and will again, have to redetermine.
One wonders how uniform your formulation is, and how well it can stay mixed. Or if the piezo isn't altering the distribution as it sprays.
Even before testing, you may want to try it and see. WHat actually happens when you put your ink formulation into the cartridge and try to print.