Garage sales and antique stores abound with old canning jars. These jars were, and still are, produced by a number of companies. Americans refer to these jars, regardless of the manufacturer, as "mason jars," because the first canning jars patented in the United States were produced by John L. Mason. Antique canning jars may be worth thousands of dollars depending on their manufacturer, size, color and condition. Apart from having the jar appraised by an expert, there is no surefire way to know if your jar is antique. However, antique jars have a few key characteristics.
Examine the text on the jar for a date. Jars produced before 1900 are more likely to have the patent date on the front, along with the manufacturer's name. Your jar could still be antique without this notation, but the date is a clear hallmark of an older jar.
Read and make a note of the rest of the raised text on the front of the jar. Some types of jars were produced during limited time periods. For example, jars that say "ABGA Mason Perfect" were produced only in the 1920s, according to Kyle Husfloen, author of "Antique Trader Answers to Questions about Antiques & Collectibles." Because several manufacturers made many different types of jars, you may need to consult a reference book or antique dealer to determine what era the text indicates.
Examine the color of the jar. Most modern canning jars are clear, which allows you to see the contents of the jar. A blue, green, red, amber or yellow jar may be antique.
Remove the lid and look at the mouth of the jar. Ground edges on the jar that are not perfectly smooth and machined usually indicate an older jar.
Determine the size of the jar, or read the notation on the front to see how much the jar holds. Typical modern canning jars come in pint, quart, 2 quarts, 4 ounces or 8-ounce sizes. If your jar is an unusual size, such as a half-gallon, your jar may be antique.