how deep are the scratches? Anything but the shallowest scratches will probably have to be sanded out first. Black should be used after fine sanding to get out the sanding scratches and prepare for polishing. It is not intended to 'repair' the surface or take out scratching but to make an already repaired and satin finish shiny.
As for the loading you should hold the compound to the wheel for between 1 and 2 secs every few minutes.
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