Periodically, I see a post on an internet art forum along the lines of “Why buy expensive mediums when leftover bacon grease works just as well? I’ve been using it since 1953 and I’ve had no problems so far!” People (especially we Americans) seem to have a strong desire to use the materials we are familiar with, have left over from other activities, or can get for a dollar less per gallon than an “equivalent” material at the art store. So you see artists using white house paint to prime their canvases, cheap boiled oil from the hardware store as a painting medium, cheap generic spray varnish, and other substitute materials.
I think that’s a false economy. I believe that, in order for paintings to be thought of as valuable, they should be made from fine materials using excellent craftsmanship. Imagine if a maker of handmade violins thought that balsa wood was just as good as a good hardwood, or that generic spray varnish produces just as good a finish and tone as a properly prepared resin varnish. That would not be an “innovative” way to save money on violin-making supplies. Working like that could possibly produce a violin that looks OK, and maybe it could even sound OK, but it would not be an object of craftsmanship.
I’m not an elitist. I have limited money to spend on art materials, too. I buy inexpensive Venice turpentine from a tack shop instead of the costly stuff from the art store, because it seems to be the same stuff and is a lot cheaper. I make my own traditional gesso panels because I can’t afford to have the guys at Real Gesso make them for me (theirs are better than mine).
I understand the desire to come up with personal solutions that feel more clever than the fancy stuff in the art store. But hardware store boiled linseed oil is junk. It’s made for tasks like protecting the wooden handle of a gardening tool from the elements, not for making permanent artwork. Adding a little bit of cheap oil (or leftover bacon grease) to your paint won’t make it explode. Painting on latex house paint “gesso” may not cause noticeable problems. The painting may last long enough, under decent conditions. And it is certainly the case that most of us will never produce a masterpiece that will deserve to hang in a museum 200 years from now.
But I can’t make paintings that way. Using house paint, cheap boiled oil, or any other junk material makes me feel like a hack, not a craftsman. Decent materials are not that expensive. And while junk materials may work out OK, they may well not, and they may cause a good painting to fail prematurely. Plenty of 19th century painters discovered that when they forgot the traditions of craftsmanship and just used whatever seemed to work they often got paintings that didn’t last. While I sometimes hear anecdotal stories about any number of weird materials being used with “no problems so far,” my own bias is to use quality materials from companies I trust, not jury-rigged stuff that is “just as good.”