Bottles produced during the last twenty years of the last century will show evidence of this twisting motion which left faint concentric rings around the mouth and upper part of the neck. This motion also erased the mold seam in the process. This is shown in the picture below on a bottle made sometime between 1890 and 1910. The lip, a round band, was finished with a lipping tool which erased the mold seam and left its tell tale concentric rings. Earlier bottles, those made before 1870, will not show these rings and lip may be more crudely applied with some drippy areas under the applied band.
Bases Looking at the base of a bottle is also helpful in determining the age.
The punty rod was used to hold the hot bottle while the lip was formed and finished. The punty rod was dipped into hot glass and attached to the base of the bottle by one of the helpers. The glassblower then formed the lip in the appropriate style and the punty rod was broken off. Larger bottles and especially soda bottles made between 1840 and 1855 have pontil marks. Most bottles dating before 1855 will have an open pontil.