Date a fairly medium dating
For instance, cobalt oxide added in proper quantities to a properly prepared glass batch results in a distinctly intense blue as shown in the bottle to the left.In fact, this color is known as "cobalt blue" in the glass manufacturing world (Scholes 1952).For example, if one has a colorless ("clear") bottle which was de-colorized with selenium and/or arsenic which gives the thick parts of the glass a subtle "straw" tint, it very likely dates no earlier than World War I (1914-1918) and infrequent in bottles after the 1940s or early 1950s (Kendrick 1963; Lockhart pers. There are also some colors which where very rarely used for one type of bottle (i.e., cobalt blue for cylinder liquor bottles is very uncommon though do exist) but quite common in others (e.g., cobalt blue for poison bottles or Civil War/Antebellum era soda water bottles).
Having quoted this, color is still an important descriptive element for the recordation and classification of bottles.
Bottle colors also warrant coverage here simply because they are of fascinating interest to people.
As implied in the quote above, there are some time related trends in color that can be of utility for dating. The specific "diagnostic utility" of a given color is noted in the descriptions below.
In the following color descriptions, the different coloring (and de-coloring) agents or compounds for the different colors are briefly noted.
This is just informational because the actual chemistry is of little utility and glass colors only contribute a little to the process of dating or typing historic bottles.