Art-to-Go from the Baltimore Museum of Art (for all ages)
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Every month in the school year the Baltimore Museum of Art picks a piece of art in their collection, writes up an art theory lesson for that piece, including an art project, and makes the lesson and a high quality photograph of the piece available for free download. This is the third school year they've done it, and the archives are freely available. The art they've chosen is stunning, and the projects tend to be managable at home, assuming you have or are willing to purchase materials when necessary. The collection includes art from a wide range of locations and time periods, and many different media.