Thanks Jo .. I have a half dozen that I will use the backside for studies ...
Just for the heck of it, as an emperiment,. I took one that I had painted and had failed. I took a masonite panel and covered it in oil paint and then stuck the paper to the panel painted side down into the oil paint. It took a while to dry as I forgot to put a hardner in it but it looks like a very good panel to me. That to me is how I adhere oil paint to a panel .. oil paint to oil paint. I'm sure it won't come undone.