I recently ordered this ink pad from here, but it's very dry. I can barely get a stamp to pick up any ink from it. Have you had this experience with any of the Adirondacks? Maybe it's just old and I should contact Ranger customer service.
Try this: store it upside down for a few days, and see if the ink comes off the bottom of the pad.
White inks of all types are typically more difficult. You may have gotten a bad pad, or I know some pads are shipped dry and come with a re-inker, and you have to ink it yourself, rather than coming already loaded with ink. I don't know if that is the case or not for this.