You need to stabilize the board by first sealing the back. Very large panels may need a 1” x 2” frame on the backside, or a thicker boards as they are less likely to warp. Birch panel hollow core doors will remain flat but seal the back first with a coat of paint.
For aluminum, place the plate between 2 plastic bags and pour some 91% isopropyl alcohol on the surface. Wait 30 minutes then wipe it off with paper towels. I have not tried this on wood yet, but if you do, you’ll need to sand the wood to remove what is left.