Instructions
Examine the ribs. The valuable Pitkin flasks from Pitkin Glass Works in Connecticut contain between 32 and 36 ribs. This type of flask became so popular that ribbed flasks made all over the country became known as "Pitkins." These Pitkin knockoffs contain anywhere from 16 to 44 ribs. Poison bottles often had vertical ribs for easy identification in the dark. Bottles for holding sauces might have vertical, horizontal or spiral ribs to make them easy to pick up.
Examine the shape of the bottle. A long, narrow shape that ends in a fluted top as if it could be used for pouring ketchup or pepper sauce probably was. Bitters bottles often came in novelty shapes such as log cabins, ears of corn or barrels. Many bitters bottles were square. Pitkin flasks were flat and oval in shape.
Look for imprinted words. Poison bottles sometimes were imprinted with the words "Not to Be Taken." Bitters bottles were often imprinted with the word "Bitters" or the manufacturers' names. The name of the bottle manufacturer may be imprinted on the bottle, too.
Check the color. Antique poison bottles often came in bright green so they could be easily seen in the daylight. A bitters bottle would more likely come in olive or light green. Pitkin flasks were made in olive green or amber.
Measure the ounces of the bottle by filling the bottle with water, leaving about 1 inch at the top. Pour the water into a measuring cup. Pitkin flasks held from several ounces to almost a pint. Sauce bottles were usually 12 oz. or less. Bitters and poison bottles were all sizes.
Look for a picture of your bottle in books on antique bottle collecting. Search for titles on websites, such as Antiquebottles.com. You also can study pictures on antique bottle sites, including Bottlebooks.com and the Historic Glass Bottle Identification &Information Website (hosted by the Society for Historical Archaeology).