Matchstickman, I'm also a gridder.
I don't think you mean upsidedown but creating a mirror image.
You make a mirror image when you do block printing.
Like Pat, I also use soft pastels to put an image on my canvas etc. I usually use a white or light color because I'm usually painting on a darker toned surface. I have also used oil pastels for this task but prefer the soft pastel.
On large simple subjects where a precission drawing is not required but all I need to do is just to locate my objects and have a reasonable size and shape, I have turned my scaled master into a stencil and stencilled a broken outline of my subjects onto my canvas with acrylic paint.
Your question has made me ponder the idea. I wonder if I did a reverse image drawning (like my block printing) on my gridded paper and covered it with oil pastels just using the local color of each object, then I could tape it to my canvas and transfer that image to my canvas, masonite etc by stroking firmly with my paper stump.
I like the idea, I'm going to have to try it. It just might work if I used a softer oil pastel such as Senneliers.
Pat can I patent this process???
Thank you for the question Matchstickman.