Friday, March 25, 2016

Archaeological Dating Techniques

We are in the final stages of processing the 2015 Fort Hunter collection and have begun to inventory the artifacts. As described in our Processing the Fort Hunter Collection blog the inventory process includes, “adding a description of each artifact or group of like artifacts into the digital inventory by catalog number, and bag and box them carefully to insure their preservation for long-term curation. This is all done in a systematic manner so that any given artifact can be easily accessed and utilized by future researchers.” During this process we try to add as much information to the inventory as we can that may be useful to a researcher and for us in our site analysis.  This includes material types, condition or wholeness of the artifact, and date of production to name a few. Many of these characteristics are easy to identify just by looking at the artifact, but determining the date or date range of production is not always easy. Over the years archaeologists have identified different methods on how to date different types of artifacts. We will take a look at some of these techniques here.

                After years of research through historical documentation and through precise data collection from well stratified and dated archaeological sites, archaeologists have developed typologies for several different categories of artifacts such as ceramics, pipe stems, bead, projectile points and more. A typology is a system that uses physical characteristics to place artifacts into specific classifications. In the case of a dating typology archaeologists use the physical characteristics to identify the artifact within a specific type that correlates to a specific date or range of dates. 

One example of this analysis method is historic ceramics which have been in production for hundreds of years, but not every type of ceramic has been in production for that entire period. Due to technological advances especially during the mid-16th to mid-17th centuries, pottery craftsmen were able to create more refined pastes (less porous), glazes more purified in color and new methods of decorating the pottery (from hand painted to transfer printed) as time went on. It is these changes in how the ceramics were produced that created subtle clues to help the discerning eye determine the specific type of ceramic. In the case of ceramics it can be difficult to identify creamware from pearlware, whiteware and others, but through previous research we know that the paste in creamware is more porous than that of the others and that the glaze is often pooled with a green tint in crevices. It is often these physical attributes that help identify a specific ceramic as creamware. Once we have identified the piece as creamware we can then look at known production or manufacture dates from the typology and determine a date between 1760 and 1820 (Deetz 1996).

Ceramic typology on exhibit in the archaeology section department of the State Museum

                When we have an entire or even a large fragment of a ceramic vessel, we can often determine the shape of the vessel or the type and method of production of the design on the vessel. Both of these characteristics are also used to narrow down a date range. So not only do we have a typology based on the type of ceramic, but we also have typologies with determined dates of manufacture for each of the different shapes and forms of decoration.   Researchers comb through archives for manufacturing records which also aid in dating these historic period ceramics.

Prehistoric Pottery & Projectile Points
Dating methods for prehistoric ceramics are dependent on typologies which were developed through careful analysis of such attributes as temper, decoration, design and form. For many native groups’ specific tempers, forms, designs and/or decorations have been attributed. Through many years of work on archaeological sites of different specific native groups a typology of pottery has been developed. Today many vessels can be easily identified with the use of this typology because there are so many different styles, each of which is attributed to different culture groups and periods. This is true of large fragments or whole vessels, but when it comes to small fragments with limited design or decoration on them, like using the porosity of the paste in historic ceramics. Archaeologists must use the temper type to determine where the pottery originated or if it could help identify what group occupied a site when combined with other evidence. Temper is a material foreign to the clay which is added to help prevent the vessel from cracking or breaking during the drying and firing processes.  Common Pennsylvania tempers include chert, quartz, limestone, shell and more. 

Example of pottery fragments with varying temper types. From left to right shell, quartz and chert

                The same process of collecting data from various sites over many years has also provided archaeologists with a projectile point typology. These typologies like that of the prehistoric pottery vary from region to region, but each typology is developed using the shape, size and lithic type of projectile points and context in which they were recovered.

Part of the projectile point typology on exhibit in the archaeology section department of the State Museum

Glass Bottles
                As with historic ceramics, archaeologists have developed typologies of glass bottles based on various physical characteristics. One part of the typology looks at the bottle lip or rim. Several types of lips were put onto glass bottles using different methods. So, as with the ceramics, archaeologists can attribute different lips to a date range because as new technologies or methods of attaching lips to bottles were developed other methods were outmoded and the newer methods were used more frequently. This is also the case with the form or shape of the bottles. The shape of the bottle base changed over time as push-ups became more or less popular and round versus oval came in and out of use. There is also the use of molds, which leave mold seams on the glass that provide archaeologists with another dating tool. Finally, if a bottle has a seal or is embossed with a company name, archaeologists can find information relating to that company to determine the bottles time range of manufacture.  There are many ways we can date a bottle and for more in-depth information on this process please check out the Society for Historical Archaeology’s website at

Picture of various glass bottles courtesy of SHA bottle identification website

Picture of various bottle base types courtesy of SHA bottle identification website

Picture of a bottle with a push-up courtesy of SHA bottle identification website

Pipe stems
                Another example of the use of a typology to determine the production date of an artifact is white clay smoking pipes, referred to as kaolin or ball clay pipes. In the case of pipe stems as with many artifacts, it is the advancement or change in technology and form that allows archaeologists to develop typologies. Based on historic documentation the length of pipe stems increased as time went on and in order to bore a hole through such long stems with no damage to the wall of the stem the size of the wire used to bore the hole had to decrease (Hume 1969). After a study of thousands of pipes both American and English one Mr. J.C. Harrington developed a system showing average bore diameter size and its correlating production date (Deetz 1996, Hume 1969). Today this system though still in debate about its accuracy, is widely used to determine the general date ranges of pipes with attached stems and pipe stem fragments, which provides useful information about the use of a site during different periods.


Picture comparing 4/64th, 5/64th and 6/64th pipe stem diameters

As shown above there are many different typologies that archaeologists have developed in order to help us date artifacts and thus date different levels of sites. Those mentioned above are just a few of the typologies archaeologists use there are also bead, drinking glass, button, coin and many other historic artifact typologies as well as prehistoric artifact typologies such as projectile points and pottery. There are also ways to help narrow down dates to more definite ranges with the use of maker’s marks.

Makers Marks
                A maker’s mark is basically a logo or trademark, which can include images, words, initials or dates that represent the maker of the product on which the mark is placed. These marks were placed on all kinds of products including glass bottles, ceramic vessels, various forms of metal objects and many other types of artifacts. Through registries and historical research it is now possible to find published lists of maker’s marks for both American and English companies, which show images of and describe maker’s marks and provide the date range of production for anything with that mark.   

Picture of maker’s mark on artifact with image and date from documentation

Identifying the dates of manufacture of artifacts helps archaeologists to not only date the level of a site, but also understand the use of the land during that period. Doing this also allows archaeologists to compare sites with similar artifacts and dates to find similarities or dissimilarities that can help us to develop theories on types of sites and their use.

We hope you have enjoyed this look into the analysis and research methods employed by archaeologists and will consider reviewing some of the resources listed below. Our job as archaeologists and curators offers us a unique opportunity to examine archaeologically recovered specimens and create a picture of past human behavior through our material culture. Please visit our gallery of Anthropology and Archaeology on the second floor of The State Museum of Pennsylvania where you can view additional artifacts representing our archaeological heritage.

References and additional information:

Deetz, James
1996       In Small Things Forgotten: An Archaeology of Early American Life. Anchor Doubleday, New York.
Hume, Ivor Noel,
                1969       A Guide to Artifacts of Colonial America. University of Pennsylvania Press, Philadelphia.

For more information, visit or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .

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