I frequently use a grid to enlarge designs for paintings. It’s my preferred method for transferring designs from one medium into another (except watercolors).
What do I use to create a grid? Good question. The grid should be visible enough to see—doh!—and not easily rub away, but not so visible that it appears in the finished painting.
Here’s a technique I developed. First, I apply three coats of gesso to the canvas. I like a smooth surface so I thoroughly sand each layer. I use acrylic gesso for canvases and traditional gesso for wood and canvas board.
After the third coat has been sanded, I apply the grid. I use a 4H pencil for small paintings and chalk lines from a chalk box for larger ones.
Then, I apply the final ground. I use a traditional oil-based ground (lead or titanium white mixed with chalk, or something similar). The oil ground is spread thinly over the surface with a long, flat knife. The grid remains visible although partially obscured—perfect! Once the ground is dry (about a week), I sand the surface once again.
The finished canvas has a clearly visible grid that cannot be rubbed away, yet is easily covered.
You can substitute acrylic or traditional gesso for the oil ground, by the way. I like the oil ground because of the way it handles.