Here is what metallic silver spray paint can look like if you try to spray it with Poly and you haven't "treated" it first.
See how it goes very dark!?
Here is how it will look if you spray the car wax first.
All you need to do is paint your piece with the metallic spray paint of your choice. I used Valspar metallic silver here. Once the paint dries, spray the entire surface with the spray wax. Use a paper towel to wipe it around, keep wiping until dry. Then, you can start spraying your Poly. Here is another tip about the Poly. Back away from the piece you are spraying! Really! Hold the can AT LEAST 12" away so that you have a light mist instead of a hard stream. Resist the urge to get close! Do 2 or 3 light misting coats and you'll be all set! You can respray the wax between coats too!
**Note if you are using a mirrored look spray paint, it will be dulled down, but will still be light and silver, like the table above.
More on the table soon.
Hope these couple of tips help with your metallic silver spray paint adventures!!