I love painting mini paintings, 5"x7", 6"x6", 8"x8", 9"x12", and so on, but the smaller the surface gets, the harder it is to put it on my easel to paint on. So, here is what I do to solve the problem.
I would suggest using 1/8" foamboard, but if you don't have it, you can also use 3/16".
1. Say for instance I want to paint a 5"x 7" painting, (this will work for 6"x6", 8"x8", and sizes in between also), take 2 pieces of foamboard the same size and cut a whole out of one of the pieces the size of support you will be using.
Because I often use Ampersand Pastelbord, I laid a piece down onto the board, traced it, and cut it out. These pieces are 11"x14" and the opening I cut is 5"x7"
2. Here are the two pieces together and the cutter I used.
3. I turned the piece over to the back side (because there is a label I can't get off...yes that is Jerry's Profoam Board) and near the edge put double sided tape.
4. I peeled off the paper to reveal the tape and then put both pieces of board together and pressed on them to allow the tape to bond them together. I also permanently bonded the boards together by applying masking tape. Now the whole thing is secure.
5. I'm ready to put my board into the hole, but first I roll up a piece of masking take and apply it to the back of the board. That holds it in the opening more securely. Only use masking tape if you are using Ampersand Pastelboard !!
If you're using paper, hinge the paper to foamcore, and put a piece of low tack tape on the back of the board. It will make it much easier to take the board out when you're done painting.
6. Ok, here is the board in the opening and it is ready to go up on my easel.
7. All set and ready to paint!!
Just remember, this doesn't have to be pretty because you'll end up getting paint/pasels all over the boards. And, you can reuse this every time you want to paint a 5"x7" painting.
I've made up lots of sizes and use them over and over.