Every day on our site, we find a rainbow of different colored bottle glass. We often get questions about these different colors. Does green glass mean that the bottle held wine? What can color actually tell us?
In order to make glass, three basic ingredients are required: sand, soda-ash, and lime (not the fruit, but the mineral). When heating these three ingredients together, the iron found naturally in sand turns the glass green. This is known as “natural” glass. In order to make colors other than green, glass-makers need to first add ingredients to cancel out the iron and then other ingredients to add color. For example, the element manganese helps to turn glass purple while the elements cobalt and copper turn glass a rich, deep blue.
Although color is one of the first things you will notice when looking at bottle glass, it really can’t tell us a lot about when the glass was made or for what might have been in the bottle. The many of the shades of green, aqua, and amber we find when we dig were used in glass making for hundreds of years and made to hold all different types of liquids. Even if one color might be uncommon to find during a certain time period, it doesn’t mean it wasn’t used at all during that time.
So you may be wondering: if color can’t tell us much information, what’s the best way to tell how old bottle is or what it might have held? The answer is by looking at its shape. For example, bottles that were made later by machines look very different from bottles made by hand. Designs and words started to be molded into glass starting in the 1800s. Medicine and toiletry bottles are much smaller in shape than wine bottles. It may be impossible to tell a bottle’s shape from the tiny fragments we find at our site, but our larger pieces can help us learn more about our site.