I dug what I would classify as a darker, cobalt blue jar in an old dump that I've been pulling 20's to 60's jars out of. I see the general consensus is that the darker bottles are from the 40's and prior. I did find this site, which I'm sure many of you use. https://www.glassbottlemarks.com/bottlemarks-5/ which says that the maker's mark of a triangle inside another triangle dates the bottles between the 1910's and 1930's, then the single triangle with Vicks/Vapo Rub encircling it being produced from the 1940's on. My jar has the latter, so the 1940's is a good guess. I think determining exact date is going to be far harder to accomplish. If anyone finds anything more, please feel free to update... even though this hasn't been updated since 2009...
