Hi, i’ve just started to learn how to paint on wood.I aieppld gesso on a plywood but when i start sketching on it, the pencil’s lead scratched the gesso and took off some of it.It’s the same when i tried to erase some sketches with the eraser, the pencil line will still be there.Instead, it’s the gesso being taken off.I waited for the gesso to dry before i sketch on it.How do i do it correctly?