American business firms preferred glass bottles in which to package their commercial products and used them extensively from the late 18th century on. Bitters bottles contained “medicine” (actually having flavored alcohol). Spirit flasks from the 19th century were blown in special designed molds with varied motifs including political subjects, railroad trains, and symbolic devices. From the 20th century, early pop and beer bottles are very collectible, as is nearly every extinct commercial container. Dairy bottles are a relatively new area of interest. Bottles may be dated by7 the methods used in their production. For instance, a rough pontil indicates a date before 1845. After the bottle was blown, a pontil rod was attached to the bottom with a glob of molten glass acting as the glue. This allowed the glassblower to continue to manipulate the extremely hot bottle until it was finished. A seam that reaches from base to lip marks a machine bottle from after 1903, while an applied or hand-finished lip point to an early mold-blown bottle.