Dating antique coke bottles
One exception are those produced during 1942-45; these were blue due to the copper shortage for WWII (copper gives the green color).
There are also some amber colored hobble-skirt bottles.
Amber-colored bottles, sold widely in the South and Midwest, tend to be more valuable than the clear or light green or flint straight-sided bottles that were more common in other parts of the country.
Petretti's guide calls this era a "gold mine" for collectors.
Be careful of Coke bottles with a deep purple color.
Here are purple examples of a S-S and 1915 Hobbleskirt.
According to the Petretti book on Coke bottles, the repro labels have even/straight/uniform lines while the originals had uneven/dotted lines.
By 1917 Cokes started being produced in the familiar hobble-skirt shape which is still used today.
You can find an enormous variation in the sizes, colors and markings of bottles.