Each aspect of the bottle's design, age and character must be taken into consideration when determining its value.A bottle that has a beautiful, interesting or significant design will generally be more valuable than one that is plain.The pontil mark is the mark at the bottom of the bottle where it was attached to the glass blower's pontil rod.
Being able to accurately identify old bottles is a skill that takes practice and experience.
The seam on an ABM bottle will run all the way up the bottle and over the lip.
As with any collectible item, the condition of the bottle will play a significant role in its value.
Digger Odell Publications provides some information and plenty of paid guides on various types of bottles.
You can find free articles here on bottle basics, reproductions, what federal law prohibits, and drug bottles.
Demand is one of the primary factors in knowing the value of old bottles.