I have recently aquired a Victorian Crown Newcastle-upon-Tyne City Police Helmet Plate.
Over the years, someone has removed the original black paint from the badge & it has been polished.
Should I leave it "as is"? What are members opinions on re-painting helmet plates? If re-painting is considered okay then should it be gloss black or matt black? I appreciate any help at all.
Thank you.
Dave.

I would leave the badge exactly as it is. Especially if it is brass. The more you do to a badge, the more it becomes worn and not in its original condition.