The base of a bottle typically only has one primary function besides helping hold the bottle together and that is to provide a flat surface for the bottle to stand upright. The following is from the British Glass website and explains it at least in part:. Bottle bottoms aren't flat because they need an arched structure to allow them to be stable on a flat surface. The bottom of a bottle is usually the thickest part, retaining more temperature throughout the production line. Because the bottom is hotter, it is also more fluid and has a tendency to sag, forming a shape like a spinning top which makes it unstable on flat surfaces. Giving a bottle an arched shape at the bottom means that if it does sag, it can do so without touching the bottom.
The identification of glass markings on the bottom or sides of a jar can help you determine which company made it and when, where, and how it was made. All of this information helps determine the jar or bottle's relative value. But even if your jar turns out to be a common variety, discovering its history is still an interesting quest. Start by looking up the logo or maker's mark. Then investigate some of the other marks on the jar that can give you a clue as to how it was made. Finally, refer to an antique bottle guide to determine if the shape, color and lid of your jar is particularly rare or valuable.
If you can your own fruits and vegetables, you might be surprised to find the value of old canning jars is often significant, with some examples reaching into the thousands of dollars. If you are using the ones your grandmother left you, that jar of spiced peaches might be worth more than you think. However, these are a few notable examples of what your canning jar could be worth:. If you are an aspiring collector, you may want to pick up a copy of Redbook 9 , available on Amazon. This book is no longer is print, but it is avaialble on secondary markets and you can get descriptions and basic values of your jars.