Salvaged items—including grates, grills and picture frames—look perfect on weathered outdoor walls. More ideas for vintage finds: http://www.midwestliving.com/homes/decorating-ideas/decorating-ideas-for-vintage-finds/page/29/0
How to Weather-Proof Indoor Art for Outdoor Use by 7thhouseontheleft. Thompson's WaterSeal, a tarp and a 1 gallon multi purpose sprayer. Then seal back with liquid nail and Tyvek. See post for securing to outside wall.