Hi. As John mentioned in another thread recently, try using a suspect painted repro as a 'pencil' and 'drawing' with it across a piece of paper - if it's painted it should leave behind a residue. If it's plastic it'll just leave an indent. Put up a picture if still unsure and we'll take a look.
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Paul F,
thevintagetoyadvertiser.org 1970s and 80s vintage toy ads and other retro paperworks
imperialgunnery.com Vintage Star Wars action figure weapons and accessories guide