Four quadrant dating
Occasionally, it appears that when the pontil rod was removed from the base of a bottle little or no glass and/or iron residue was left behind to indicate that a pontil rod was used.
The reasons this occurs are unknown but may just be chance or certain glass making related conditions.
The point here is that close scrutiny is often necessary to conclude that a pontil rod was not used in the manufacture of what appears to otherwise be a very early bottle.
The rest of this section is an overview of the main types of pontil scars: glass tipped pontil scar, blowpipe pontil scar, sand pontil scar, and bare iron pontil scar.
The common mode heretofore employed has been to use a straight bar or rod of iron with a head or ball upon one end, to which, when it is dipped into the melted glass, a quantity of glass adheres.
While in a semi-fluid or plastic state, and while the bottle is also in a plastic state, immediately after being withdrawn from the mold, the glass upon the rod or punty is brought in contact with the base or bottom of the bottle and immediately it adheres thereto, and the glass soon chilled, the bottle is made fast to the punty, so that the operator may finish the neck of the bottle in any desired form.
The base of a bottle which was held with a pontil rod will almost always retain some evidence of the pontil rod attachment. (It should be noted that bottles having no evidence of a pontil scar of any type are typically referred to as having a "smooth base;" click smooth base to see that discussion on the Bottle Glossary page.)The following description of this process is from an 1865 patent (U. Patent #51,058) for an "Improved Clamping-Punty" - a patent for one of many improved grasping devices which replaced the pontil rod and were a much quicker method of holding a bottle by its base for finishing.Farnsworth & Walthall (2011) found in their monumental study of Illinois bottles produced between 1840 to 1880, that bottles made by East Coast glass houses were smooth based beginning about 1856, whereas bottles produced in and around Pittsburgh, PA.("Midwestern" glass houses) did not produce smooth base bottles (i.e., used snap case tools) until about 1860.Fire polishing was done to remove tool and mold marks and to achieve an esthetic shiny surface to the glass much like later turn-mold bottles achieved through a different process (Ketcham 1975; Toulouse 1969).Fire polishing would sometimes remove most or all evidence of the pontil scar making a very early bottle appear to be a later smooth base bottle.