In the previous millenium when I was an avid photo hobbyist there was a product for coating ferrotype plates. It was a liquid and I think it was referred to as a wax, but it was unlike any auto wax. A very thin coating was rubbed on the plate with a soft cloth then buffed when dry. I remember that it resulted in vastly improved glossy prints compared to a plate without the treatment. Keep in mind that any irregularities on the plate surface are transferred to the shiny print surface. A scratch on the plate will look like a crack on the print.