CMR Museum hosts outdoor painting event CMR Museum hosts outdoor painting event and last updated 2021-07-25 23:04:23-04 GREAT FALLS â On the grounds of the C.M. Russell Museum in Great Falls on Sunday, the Arts Association of Montana hosted a free plein painting event. En plein air, or plein air painting, is the act of leaving the art studio and painting outdoors. The Arts Association of Montana is a non-profit organization that promotes appreciation, awareness and enthusiasm for all art forms in the Treasure State. The organization offers workshops to the public with plein air outings and day trips to encourage artists to grow through education.