Posted By:
davidcyclebackI would think in general, 19th century paint looks distinctly different than recent paint-- cracking, aging, etc. I recently looked at a repro bubblegum machine and the red paint was obviously brand new-- very clean, smooth and bright. I'm no bubblegum machine historian, but from six feet away I correctly guessed the paint was new.
I believe the blacklight test would be for the overall paint, not the ink writing. I suspect most modern black pen ink doesn't fluoresce.
Also, the same test is used on varnished items, as varnish also loses fluorescence with age. Antique fishing lures were commonly originally varnished, so collectors often put their lures under a blacklight.