Recently we were given a large number of free canning jars in various sizes about 10 cases. My wife was happy to get them and thought that it was a great deal. Unfortunately, there was a catch. When you started using the jars, they worked fine when you used them in water bath canning. When you tried to use them for pressure, canning the problem started.
The bottoms were failing and falling out of the jars. This was only happening to the ones we got for free. The break was similar to the ones you get from thermal shock with the break running around the base of the jar. Because of the way in which she cans we know it wasn’t her problem. She is an experienced canner and all her other jars were coming out fine.
The one thing that immediately popped into our minds was the way the canning jars had been stored prior to our getting them. They had been stored outside in a lean-to in cardboard boxes and exposed to the heat and cold for at least 5 or 6 years. The temperatures ranged from below freezing to over a 100° F. I think that the constant changes in temperature weakened the glass.
They work fine for vacuum sealing and water bath canning, but not pressure canning. So we will only be using the rest of the jars for limited purposes. My wife intends to make a black X on the bottom so that she can identify them.
Up until now, we have never worried about the temperature in which we stored canning jars. But in the future, we will make sure they are stored under the best possible condition inside with moderate temperatures.