By 1800 this diameter had decreased to 4/64 of an inch.
This change in diameter may have occurred because pipe stems became longer through time, requiring a smaller bore.
Few makers incorporated dates into their marks, though the practice of marking pipes probably initially coincided with the establishment of the London tobacco pipe guild in 1619 and continued into the 19th century (Nol Hume 2003-4).
Archaeologists analyze multiple clues to date and identify the pipe maker including a careful combination of archaeological site context, bowl style and form, pipe stem bore diameter, style and placement of the mark itself, and place of manufacture.
When using bowl typologies, we also acknowledge Nol Humes caveat (194) that we suspect remains as valid today as it was 45 years ago: There is, unfortunately, a great deal that we do not yet know about the so-called evolution of bowls and stems, and there is reason to suspect that present stylistic and dating criteria have been oversimplified. For example: Atkinson, David and Adrian Oswald 1980 The Dating and Typology of Clay Pipes Bearing the Royal Arms.
Tobacco pipe makers marks appear in a variety of locations on the bowl including on the back, front, and sides, on the base, and on the sides of the spur or heel. Marks were produced by molds that left incuse (negative) or relief (raised) impressions (Oswald 19-91).
Two recent studies of collections in western Kansas failed to document any point types of this time period.
Historical archeologists do not rely on pipe stem fragments as the only source for determining a site's history.
They also consider historical documents and other material culture recovered from the site—such as ceramics, glass, metal artifacts, faunal and botanical samples, and features—to determine its occupation and use.
The period comes to a close with the gradual onset of a period of warmer and drier climate called the Altithermal.
This time period coincides roughly with the climatic episode known as the Altithermal.