Instructions
Look at the color of the jar. Originally, Mason jars were an aquamarine color. These are the very first Mason jars ever created, and they're quite valuable. Later, pink chemicals were added to the glass in an attempt to make it clear. Though this did nothing more than turn the glass a murky, purplish pink, these Mason jars have been appraised at $42,000.
From 1900 to 1920, Mason jars were created in many colors, the most popular being amber, burgundy, and cobalt.
Examine the bottom of the jar. Richard Cole, a Mason jar aficionado, says that Mason jars were embossed with the words "Mason's Patent Nov. 30, 1858" up until 1900, 21 years after the original patent expired. Newer jars don't have this stamp.
Look at the jar's lid. The original Mason jar had a rubberized seal on the center of the cap that allowed the lid to stick to the jar with suction, preserving the food inside. This is the design that John Mason patented. If a Mason jar doesn't include a rubberized sealing lid, it's worth significantly less.
Find square Mason jars. They have an embossed Ball label in the center of the jar, and they also have the patent stamp on the bottom of the jar. These jars were originally used for holding moonshine during Prohibition. They are no longer made and are extremely rare.