If it's around #15 or greater, but unlike the eclipse you won't be able to see anything interesting with just the welding mask. Mercury is too small. You need m

If it's around #15 or greater, but unlike the eclipse you won't be able to see anything interesting with just the welding mask. Mercury is too small. You need magnification, but if you use binoculars and you put the welding mask between the binocs and your eyes you will permanently damage your eyes and the binocs. Make a pinhole in a playing card and put a large piece of white cardboard a meter behind it. This will work well. It will be dim so you might need to arrange a large sheet of poster board around the playing card for shade.