The shelf life of gold toner is indefinite, so you can store the solution between sessions. But the solution is depleted by the toning process, and it slows down as it becomes depleted. The capacity depends on how deeply you tone, the area of the prints, and the average density of the prints. You should be able to get about 30 5X7 prints per liter from most solutions. Most gold toners can be replenished to keep the activity consistent.