Old Mason jars are one of the internets best-kept secret gold mines. One great example is the ultra-rare upside-down Ball Mason jar. This glassware piece was only issued from 1900 to 1910. Now, its worth about $1,000.

Do old blue mason jars have lead?

All Weck Jars I have tested have been positive for lead in the 200 ppm range (still very low, but consistently higher.)