As part of my Xmas fettling efforts, I’ve also started work on this late 1930s (?) PL53. The tank was very rough and covered with heavy oxidation that just wouldn’t shift with a dish scourer and hot soapy water. Decided to polish and let re-tarnish naturally. Good or bad idea? removing the heavy crust revealed a serial number too. Can anybody suggest a date from it? Money shot pic of this lantern on New Year’s Day if all goes well... by the way, what are those reddish marks on the brass? Is it ‘red rot’ (copper efflorescence)?