A Mason or Ball jar is more collectible if it is a rare variety, size or color and is in good condition. A jar is the most collectible if it has its original lid with it.
An older jar is usually more collectible. However, the age of a canning jar can be difficult to determine. Ways to estimate the age of a jar are to look for a pontil mark and to compare the logo with logos that have known dates of manufacturing. A jar that has a seam from top to bottom is machine made and dates to post 1915.
Color is a very important factor in determining if a jar is collectible. Clear glass jars are the most common and are usually the least collectible. Highly desirable colors are black, amber, milk glass, cobalt and emerald.
Canning jars have numerous styles of closures and lids that depend on age and manufacturer. A jar is not as collectible if it does not have its original closure type. For jars with glass lids, it is also important that the lid be the same color glass as the rest of the jar.
The size of a jar, or if it contains any misprinted words, also affects the desirability. Half-gallon jars are highly sought because not many of them remain in existence. Square jars are also less common and thus are more collectible.