Printer structures include a controller, a marking engine operatively (meaning directly or indirectly) connected to the controller, and a container connected to the marking engine. The marking engine applies marking material to print media, and the container stores that marking material. The container can include a flexible bladder storing the marking material, and an actuator structure operatively connected to the controller. The actuator structure contacts the flexible bladder and periodically moves portions of the bladder to periodically mix the marking material as controlled by the controller (based on the marking engine being idle for a previously established amount of time). Alternatively, the actuator structure contacts the container can periodically rotate the container to periodically mix the marking material as controlled by the controller.