To know collectible antique glass you must understand how glass was made in the days from which your collectors clamor. Blown glass was made by molten glass placed on the end of a glass tube and blown up like you blow up a balloon. As it was being blown, it was shaped by various tools and when complete it was allowed to cool.
During the making of collectible antique glass bottles, a handle may be applied by pressing the molten glass shaped like the handle onto the jar once it started to cool. Occasionally this process resulted in a crack in the bottle, which does little to detract from the current value of a collectible antique glass.
During the fashioning of blown glass, a tool called a pontil rod was used to hold the glass while it was fashioned into the desired shape. In the end it was simply snapped off and may be polished clear, but the evidence of the pontil mark should still be visible and gives a general idea of age and value of collectible antique glass.
In later years glass objects were made of molded glass and many of those were counterfeits of original blown glass. To find modern molded glass masquerading as collectible antique glass there are a couple things to look for like the wear factor. Look at the bottom of the piece first to see if you can find the pontil rod scar and then look for wear marks. If there are marks where there shouldn’t be, it’s probably a fake.
Another hint is small irregularities in the top of the piece, indicating spill over as if too much molten glass had been poured into the mold. This would be a sign of shoddy workmanship, as would too many bubbles in the glass. Although, even in quality blown glass a few bubbles may appear, but in the cheaper reproductions it won’t take long to find them.
Perhaps your first step in buying collectible antique glass should be the purchase of a collectible antique glass magazine or book. It will usually identify the collection trends and help lead you on the right collectible path.