I made a painting last October combining oil paints, oil bars, and oil pastels.  It's a commissioned piece and should have been hung last December.  Everything went beautifully except that one color (black) oil pastel refuses to dry even a little.  It's still as 'wet' as if I applied it an hour ago.  I'm a professional artist and have combined paint and pastel many times with great success.  I'm considering hanging the piece and repairing on the wall, but the intended location sees a lot of traffic from children and I'm concerned it will be one big smeary mess within a month.  My clients have been incredibly patient, but are ready to have a finished product in their possession.  I've contacted the manufacturer and, so far, they have no answers for me.  Has anyone ever heard of this before?  Any ideas?  Anything?