One of the most commonly assumed facts about archaeologists (aside from our ability to have adventures, look good in a fedora and be surprisingly skilful with a whip), is that we can look at an object and know how old it is. While this (much like the fedora and whip thing) is not true of all archaeologists, the ability to date artefacts is an integral part of the archaeological process. It is by no means the only part, but it is an important feature of our work and one that can, on occasion, be a little bit frustrating.

Today’s post is the first of three looking at how we date artefacts and assemblages; what this means for the broader archaeological interpretation of sites and people in the past; and some of the difficulties we encounter along the way. This week focuses on some of the issues involved in using evidence of manufacturing methods to date artefacts – specifically, glass bottles – and how those dates relate to the use and eventual discard of an object.

When we find artefacts at a site and get them back to the lab, one of the first things we look at is when they might have been made (even though we’re most interested in when they were used, which is not the same thing). Bottles (and other artefacts as well) are covered in physical clues that can help date when they were made, thanks to modifications in manufacturing techniques and changes in style or fashion over the decades. Such clues are visible in the seams of a bottle, its shape, the type of closure (top of the bottle) and a hundred other scars and traces left behind by the manufacturing process.

The information these scars provide can be anything from extremely broad date ranges to quite narrow periods of manufacture. There’s an obvious and highly visible distinction, for example, between 20^th century machine made bottles and (usually) pre-1900 mould or free blown bottles, but dating an artefact to one century or the other is, unfortunately, a little inexact for our purposes. On the other hand, characteristics like crown top closures (invented in 1892) or the Codd style soda bottle (patented in 1870 (UK) and 1873 (USA) and used until the early 20^th century) can help to narrow down the date to a specific decade (Lindsey 2010).

 

Unfortunately, however, some bottles have very few traces of the manufacturing process evident on the glass and can only be dated very roughly. Even when the details of manufacture are visible, we have to be aware that the transition from one manufacturing technique to another (and thus their associated dates) was never clear cut. Since these bottles were being made by individual glassmaking companies and, within that, by individual glassmakers, a lot of the variation in early bottles is as dependent on the people behind the process as it is on the technology available. It’s simultaneously one of the coolest things about 19^th century artefacts – the personal touch behind each object – and the most frustrating, from a dating perspective at least.

Fortunately, we have alternative ways of figuring out the manufacturing dates of glass vessels. As we’ve mentioned before, sometimes bottles will have a maker’s mark stamped on the base and, depending on how often a manufacturer changed their stamp (and how well documented those changes are), we can use these to establish when an artefact was made. Other times, we’ll be able to determine the contents of the bottle from embossing on the glass and figure out when that product was being made or sold – like many of the pharmaceutical and soda bottles we’ve already featured on the blog.

This is great if the product is a short-lived one that’s well documented, but more often than not we’ll come across a product like Lea & Perrins, which has been made continuously since the 1830s or one like W & W’s Double Refined Table Salt, about which very little information was available (Tasker 1989: 88). Similarly, a bottle manufacturer might have used the same maker’s mark on a bottle for a long period of time: glassmaking company Parke, Davis & Co used the same initials on its bottles from 1875 through until the 20^th century (Toulouse 1971: 417). Even if the marks do change over time, if there’s no record of those changes and when they occurred, we still can’t narrow down the date.

Sometimes a maker’s mark will only be visible as initials or a monogram that we can’t always trace back to the manufacturer. These can be some of the most frustrating artefacts to come across when you’re trying to date a site, because we know that the information is there, on the bottle, but we can’t find or access the resources to make that information useful.

And, while these bits and pieces of information might be able to tell us when a bottle was made, they don’t necessarily tell us when it was used (or how long for) and more importantly, if we’re looking at a whole site, when it might have been discarded. Most of the artefacts we find on 19^th century archaeological sites in New Zealand were made overseas and we have to consider the time it would have taken for them to reach New Zealand when we’re figuring out our dates. We also have to consider the length of time for which an object might have been used – its ‘uselife’ – before being discarded or lost, and ending up in the ground.

With bottles, this is a particular problem thanks to an issue known as bottle re-use. A lot of (if not most) 19^th century bottles would be reused many times by the contents manufacturer (or another manufacturer entirely) before being thrown out (Busch 1987).In New Zealand, this occurred in response to the absence of a local glassmaking industry until the early 20^th century and the effort involved in importing bottles from overseas. Newspapers from the time are filled with advertisements from hotels, soda water manufacturers and pharmacists offering discounts or cash for the return of bottles. There are cases of court action being brought against people or companies who failed to return bottles and were consequently convicted and fined for the offence.

Of course, from a dating perspective, issues like bottle reuse mean that the date of manufacture is almost never an accurate reflection of when a bottle was being used or eventually discarded. It’s just a starting point in the life of an artefact, one piece of information about an object that usually has a bunch of other stories to tell. It’s only when we take that starting point and look at it in light of all the information an object (and the other objects around it) can give us that it becomes a useful window into the past.

And, despite the difficulties involved in artefact dating, it is hugely important that we ask the question in the first place, because it gives us the chance to link assemblages and objects to people in the past. If we can date the use and discard of an object to a specific period, we might be able to figure out who used it and why they threw it away. It’s part of what makes context so integral to what we do, and why we get frustrated with fossickers and people who dig up sites illegally to find collectables – because in doing so, they destroy the additional information that we could have used to link an object with the people who used it.

It’s one of the most important principles of archaeology – that (unlike Indiana Jones) we’re not just interested in the things (although the things are pretty cool and very useful), we’re interested in people and what those things can tell us about them.

Jessie Garland

References

Auckland Star. [online] Available at http://paperspast.natlib.govt.nz.

Busch, J., 1987. Second Time Around: A Look at Bottle Reuse. Historical Archaeology, 21(1):67-80.

Colonist. [online] Available at http://paperspast.natlib.govt.nz.

Donaldson, B., Hume, G. & Costello, S., 1990. Antique Bottles and Containers of Christchurch and District. Christchurch Antique Bottle and Collectors Club, Christchurch.

Evening Post. [online] Available at http://paperspast.natlib.govt.nz.

Lindsey, B., 2010. Historic Glass Bottle Identification & Information Website. Society for Historical Archaeology and Bureau of Land Management. [online] Available: http://www.sha.org/bottle/index.htm.

Tasker, J., 1989. Old New Zealand Bottles and Bygones. Heinemann Reed, Auckland.

Toulouse, J. H., 1971. Bottle Makers and Their Marks. Blackburn Press, New Jersey.