Stop in for a cup of coffee

I've been using spray graphite on my existing headers for years. Haven't rusted, stays really well, look great to me. Once a year spray a bit in the cap, take a brush and do a little recoat. Then buff to nice sheen. To me it's a perfect solution for headers!
Sounds impressive. Do you guys know if I can use Slip Plate over painted parts or is it just for bare metal?