Dried out Spotone is not a problem, as if there is pigment in the bottle, you can add a bit of distilled water to the bottle. The way I used to use Spotone was to put a drop each of the different tints on a white china saucer, and let them dry out, then I would wet my spotting brush with a tiny bit of water and touch the dried pigment, to moisten it, and then mix to the tone I wanted, then spot away. I never used Spotone direct from the bottle. A complete lack of Spotone would be serious, but dried out pigment in the Spotone bottle is but a minor inconvenience.