The panel's surface is very slippery, and I'm choosing to work on it unprimed, because the image I want to paint could be very exciting if a little of that silvery color peeks through here and there.
I started by peeling back only the upper left-hand corner, and trying out regular graphite pencil and then pastel pencil in order to draw the grid lines I'll need to place the brushstrokes. (The image is mostly swirling water, so it'll be necessary to be accurate.) Neither was easy to remove. Then I tried placing tiny dots instead at the corner of each square inch, and that seems to be working well.
Here's what it looks like now: