People have been using canning jars since the 1850's. The term "mason jar" comes from the inventor of such jars, John L. Mason. Mason didn't invent the glass jar, of course. What he did was design and patent the metal screw-on lid for such jars, which made preserving food in them possible.

Mason jars used for canning have three parts. First is the glass jar itself. They typically come in one of two styles: regular and widemouth. The glass jar is usually clear, but they've been manufactured in other colors as well. Another common color is aqua. However they can also be found in pretty much any color. It may surprise you to learn that there are collectors who specialize in collecting antique mason jars. The colored ones are the most valuable as they are the rarest kind.

The second part to the canning jar is the metal screw-on ring. This ring is not as important as you might think. In fact, many experienced canners store their jars with the rings off. The main purpose of the ring has nothing to do with sealing the jar. It's just there to protect the center portion from being knocked off. Also, if the seal breaks, the metal ring will help keep the contents of the jar from going all over your cupboards or pantry.

The third piece to the mason jar is the metal center cap. This cap is ringed with a sort of rubber sealing compound which is what actually seals the jar and keeps the food inside from spoiling. Again, this piece is what seals the jar. The metal ring is there just to protect the center lid. People store their jars without that ring because it can hide a bad seal and they're prone to corroding. By storing your jars with the ring off, you can quickly ascertain the integrity of the seal.

If you ever have any doubt as to whether or not the seal's been broken, throw out the jar of food. It's best to not risk it. There is plenty of information available to assist you in determining if a seal is broken, but the advice you're going to hear and read again and again is, "When in doubt, throw it out."

Another popular lid for the mason jars is the bail closure. While not the most common form of lid, it's still fairly common. The bail closure uses a strong somewhat spring metal wire clip which when closed forces the lid down and holds it shut.

Mason jars aren't just for drinking out of! Many people use them for preserving food. That's what they're intended for, but they can also be used as decoration, especially the valuable colored ones.