Erica,
Ol' Bill did things the old way. When I showed him my method, he was astonished, and wandered why the "boys at the Zanerian" didn't think of that! The longer it sits mixed, the better and stiffer it becomes, Erica. If it should get too stiff, as taffy, add some water, but do so sparingly. When you do add it to your ink or gouache, do so sparingly.
By the way, I mix my own gouaches and always get better results than buying them. The stiffness of the GA, too, keeps the pigments suspended. The hairlines have a great definition. Overall, the stiff GA creates a perfect opacity to the gouaches--and I am very fussy about scripting, as Bill was, with the max. amount of opacity. ...enough of my blather. I hope you are well.