This is not the only way to surface-mount a small painting painted on wood or canvas board, but it is how I would do it. I know some people hesitate to purchase paintings when the framing is needed afterward, but don’t let the small effort involved scare you off. I personally don’t like to pre-frame my paintings because there are just so many frame choices available, and each one suits a room’s decor differently. It is likely I would choose a frame that I love, but which does not suit your own home decor at all. And wouldn’t you rather have the fun of making it match perfectly?
So when I was in Hobby Lobby the other day looking at the tremendous variety of frames available, it struck me that some people might look at all the open-backed frames and just think, “I have no idea how to keep a painting in that thing,” before walking off in frustration. Which is where my handy dandy tutorial comes in!
(I intend to make another tutorial for stretched-canvas paintings, but that will have to wait until I have something to photograph! You can intuit how to do it from reading this, though 
First, determine the depth of your canvas. A canvas stretched over wood stretcher bars is typically 3/4″ or greater, you need to actually measure your canvas at this point. A wood board or a canvas board is typically 1/8 of an inch thick. It will fit into most photo-frames, if you remove and discard the cardboard backing.
Sometimes a canvas size is not standard, and there will not be a ready-made frame available in that exact size. For my example I am using a 4″x8″ painting, which is not a standard size. What to do with an odd sized painting? Surface mount it, in a frame that is twice as large as one or the other of your painting’s dimensions. I have used an 8″x10″ frame for my example.
The depth of the recess in this frame is 1/2″. That means I have to fill up 1/2″ depth with cardboard cut to the 8″x10″ of the frame, after I have inserted the pretty backing paper which is visible, and which hides the cardboard.
I used a piece of pastel paper for my example, as it is a suitable color and has an interesting but not competing pattern. You can find single sheets of interesting paper at scrapbook shops, or in craft stores. You don’t have to spend over $1 for your pretty paper.
This is a photo of the back side of the frame, showing the depth filled with cardboard. It may not look like cardboard, but let’s say it is.
Back to the front side, you can see the pretty paper is held in place by the cardboard behind it, and you are ready to mount your painting by using double-sided tape. That’s all it takes. Some people use the foam double-sided tape because it adds a dimensional quality to the finished framed work.
And then back to the back side. To keep everything in place, cut a piece of craft paper slightly larger than the cardboard, because you will glue the paper directly to the back side of the frame. It is the paper that keeps everything from falling out. I did not make a photograph of this, but I’ll take a photo the next time I do it.
Finish small framed works with a sawtooth hanger, larger ones will need eye hooks and wire. I will demonstrate that in my next tutorial.
Thank you for the useful information.