I have been asked several times "how do you prepare watercolor paper to paint on with oils?" Here's my brief over-view.
"The Broach" was an experiment and a study. Probably more an "experiment" than a study since I do NOT plan to paint a larger painting of this woman. The woman is an 11" x 14" painting so it isn't tiny. It wanted to see how well I could paint on a triple primed with Gesso, a piece of 300# watercolor paper with oil paints. Keep in mind that 300# w/c paper is next to the most expensive and firmest of all watercolor papers. Only paper I'm aware of that is more expensive is Arches' very large sheets but I believe are the same weight.
The 300# won't buckle, waffle or curl when wet with water or Gesso so no need to stretch. But, if you are going to try this on lighter weight paper you will probably want to wet and pre-stretch, dry and leave it stretched BEFORE and while applying the Gesso. Once the multiple layers of Gesso are dried I suspect it will be very stable and you can remove the tape or paint on it just as it is. The 300# w/c paper works beautifully.
If you like to paint on a very smooth surface then this is your surface!
11" x 14" oil on w/c primed paper
Let each layer of Gesso dry completely before applying the next coat. Goal is to cover any nasty w/c paints on the paper and to thoroughly seal the surface so the oil does not sink into the paper. A hair dryer helps speed the process along. Sand if you want but not necessary. I applied about two coats of black acrylic paint over the Gesso and let dry before I proceeded to add oil paints.
I have applied at least a dozen layers of oil paint on the lady with the broach, along with as many layers of Liquin as I proceeded through this painting. Not all sections were painted at once nor did I cover the whole surface with Liquin every time I used it. The Liquin plus oils in thin coats has created a beautiful depth to the surface.
This is a photo of the backside of the painting. Just as nasty as the front side was before the gesso and the oil painting were applied. Two-sided failure of a watercolor! I don't throw art supplies away easily, especially expensive watercolor paper!
I think if I was going to try to sell this painting I would apply several coats of black acrylic on the back and write a lovely description of the painting in white or gold ink on the painting and sign it. Nice and clean back!
In the end I loved painting on this surface but then I really like a smooth surface to work on. Someone who likes more texture then that is also doable on this paper. Buy any number of brands of textured mediums and try it out. Sealing the surface is the first goal and after that the sky's the limit.
How well this surface would be received to sell is another
question that would have to be explored. These panels would have to be framed for sure because you see the edges, they are much lighter in weight and I would imagine most people would not hang directly on the wall. Big paintings would definitely be very light in any frame making for easier hanging on the wall. The other thing with using gessoed w/c paper is that regular craft store frames could be used easily and for far less money. If you are framing a very large painting then you might want to consider backing the painting with a foam core to help support so it did not bow over time. Not sure that would happen but worth considering.
I know there are some artists painting with oils on w/c paper that have also put glass over the oil painting on w/c paper . Basically the paintings are being finished out just like a watercolor painting except for the decision to use or not use a matt board. You could do that too if you wanted to but not necessary to matt or put glass on the front. More expensive involved also. The proper glass would also have to be installed because plain glass can cause glare on the oil painting. We wouldn't want that! The oils will stand the test of time without glass and you don't have to worry about fading.
I have also glued watercolor paper to small 6" x 6" Gessobord, Masonite and MDF panels that had nasty paintings of some other style on them but I didn't want to throw out the panels. Works beautifully but do need framing because of nasty edges.
So you can proceed with caution as to what you want to do with these paintings or how they are marketed. I hate wasting expensive w/c paper so this was a definite plus with this experiment, gave me an opportunity to try other painting styles and not care too much about messing up an expensive canvas.
If you have old, never finished and/or complete failures of watercolor paintings , stacks of unused w/c paper hanging around from when you once painted in that medium then you are ahead of the game. It's almost like FREE surfaces to paint on since you might have bought them a decade or more ago like I did - more like two decades ago really! Give this a try before you pitch the paper into the swimming pool or the trash!
Have fun and keep painting!