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Lightning in a Bottle Part 1

Updated: Jun 19

And now back to your regularly scheduled programming, Xplorers!

We’re starting off strong in 2023 with our first new blog series, which we’re affectionately calling “Lightning in a Bottle.” It’s the series where we teach you your next coolest party trick.

A collection of glass bottles of different sizes and shapes

We’re going to teach you how to analyze glass bottles.

You may not have heard, but bottles are actually super cool. They have so many nuances of design and so many features that can be customized, personalized, and otherwise-ized! They also have a long history, and they can tell us a ton about the people who left them behind.

Three amber-colored glass bottles, large, medium and small

We find them all the time — whole glass bottles, tiny glass shards, embossed pieces, glass of all variety of colors, both mouth-blown and machine-made — and we’re always excited because they can tell us so much about a site. If you know just a little bit about the different characteristic features of bottles, you can pick up any old bottle and make a pretty accurate determination of when and where it was made.

And the really cool thing about that is that we can use the information we gain from our glass bottle analysis to date sites. If we find a whole collection of artifacts, chances are, we’re not quite sure when they’re from. But because we can analyze glass bottles and find such precise dates, we can narrow down a date range for archaeological sites with ease.

That’s what this series is all about. We’ll be digging deep into each distinctive bottle feature so that you can learn to analyze bottles for yourself just like a real archaeologist. We’ll show you what to look for, teach you the difference between mouth-blown and machine-made bottles, and even how to research your bottles so you can discover more about their history. We’ll also walk you through some common types of bottles you’re likely to find around your local antique shop!

Bottle analysis is one of the most fun parts of what we do, but we couldn’t do it without our favorite trusty research source, the Society for Historical Archaeology’s Historic Glass Bottle Identification and Information website. Their site has a ton of useful information, and we use it as our field guide anytime we need a reference while we’re analyzing.

Alright, now that we’ve given appropriate credit where due, let’s dig deeper!

The Key Features of Any Bottle

When it comes to bottles, there are six key features to look out for: Shape, color, the finish (or closure), the body and its seams, the base, and maker’s marks. Each can tell us something about how and often when the bottle was made. There are many different types to look out for within each category, but remember — you don’t have to memorize them all! The SHA’s field guide is always available.

Today, we’ll be covering the first three categories, shape, color, and finish. Then, next week, we’ll cover the other three and feature a surprise glass bottle you just might be familiar with… no spoilers!


Three clear glass bottles, one short, one medium, and one tall

As you’ve probably noticed, bottles come in many shapes and sizes. Some are tall, others are short, some are round, and others are weirdly curved. The shape of a bottle can tell you a lot about what the bottle was most likely used for. For example, historically, whiskey and other liquor bottles tended to be of a pretty wide variety of shapes, but wine and champagne bottles have long been longer, taller, and skinnier.

Likewise, while whiskey bottles can come in round shapes or other shapes like squares and rectangles, soda and mineral water bottles nearly always round. It makes sense — carbonated liquid tends to move around a lot, so it needs a stronger bottle to keep it contained. Round bottles are less prone to cracking and breaking than other shapes, so round has long been preferable for soda.

Some bottles are square, others are round. Some are made to lie on their sides, with one flat side and one rounded side. Some bottles have flat sides, others have rounded or fluted or patterned sides. There’s almost no end to the variety of bottle shapes archaeologists have found out there!


Glass comes in many beautiful colors, and that’s why color is another essential element of bottle analysis. Unfortunately, color isn’t the most helpful characteristic when it comes to dating or typing bottles, but it’s still a unique characteristic worth paying attention to.

Two glass bottles, one clear and one blue

Glass bottles come in aquamarine, green, blue-green, olive green, amber, true blue, purple, amethyst, red, and plenty of other colors. It’s important to note, however, that archaeologists tend to stay away from calling glass “clear” when it doesn’t have any color because “clear” can also mean “transparent.” Instead, we’ll often call bottles without any color simply “colorless,” and bottles that have a translucent white color are known as “milk glass.” Not confusing at all, right?

Color is particularly useful for telling what the bottle was originally used for. Is it a dark amber? It was most likely used for whiskey, ale, or possibly soda. Do you have any tiny milk glass bottles? They most likely once held beauty products. Have a glass bottle in a peculiar shade of green? It was definitely — ah, no spoilers!

Finishes and Closures

Finishes, also called “lips,” are the tops of the bottles, where they close. These fall into those two categories we mentioned earlier: Mouth-blown and machine-made.

Mouth-blown glass bottles are just that — they were made by an actual human. Before we had the technology to build machines that could automate the glass-blowing processes, artisans and craftspeople had to blow the glass themselves. That process resulted in a lot of unique bottle finishes! And we mean “unique” literally — since every bottle had to be individually and specially made by a person, each one is slightly different, and each contains small imperfections.

A bottle neck with a rough and sharp cracked-off neck
Here's an example of a cracked-off finish, courtesy of the SHA website.

Mouth-blown finish types include:

  • Cracked-off – The neck of the bottle is literally broken off.

  • Fire polished – These are essentially the same as cracked off, except the bottleneck is reheated so that the broken-off edge can be smoothed off.

  • Ground – These are also essentially the same as cracked-off finishes, except the edge is ground down until it’s smooth instead of being reheated.

  • Laid-on ring – After the bottle is broken off, a short ring of glass is placed on top of the opening to give it a smooth finish.

  • Rolled or folded-in/out finish – After the bottle is removed from the blowpipe, the edge is reheated as necessary, and then it’s either rolled or folded over.

  • Flared or flanged finish – The craftsman will carefully bend the hot end of the bottleneck so that it finishes at a 90º angle.

Sketch of a tool used to create a smooth finish on a glass bottle neck.
Here's an example of a tool, also courtesy of SHA

As bottle-making technology improved, bottle makers began using finishing tools to refine their finishes. Once the bottle was removed from the mold, the neck would be reheated and smoothed with a tool. (Bonus fun fact: You can usually spot a tooled finish when you see marks indicating that the bottle neck was twisted!) Tooled finish types include:

  • Applied finishes – Popular in the mid-nineteenth century, this technique involves adding additional glass to the end of the bottle and using a tool to smooth and create a beautiful finish.

  • “Standard” tooled finish – Once the glass has been blown into a mold, a tool would be used to smooth and finish the neck. This technique is recognizable because the side seams (We’ll talk more about seams later) ends right below the finish.

  • “Improved” tooled finish – For this technique, the shape of the finish would be mostly formed in the original mold into which the glass was blown — the tool would just be used to smooth and totally polish things off.

Then there are the machine-made bottles. These are much more uniform and precise, though the visual differences from mouth-blown and even tooled finishes are subtle. There are two key things to look out for:

  • The vertical side mold seam usually runs all the way to the very top of the finish because the finish is part of the mold.

  • There is a horizontal mold seam that runs around the bottleneck right below the finish.

Check In: How Are We Doing?

Okay, we know that was a lot of information! How are you doing? Still with us? Good!

Here’s the other important thing about bottle analysis: It’s great to have these analysis tips and tricks in your back pocket, but the truth is, not even the professional archaeologists have all this stuff memorized! Trust us — when our laboratory technicians analyze artifacts from our projects, they pull out their field guides, check their notes, and match up the artifacts we’ve recovered with the pictures in their textbooks. Everyone needs a field guide from time to time!

All that to say, there’s no shame in consulting the SHA or doing a quick Google search to learn more about your glass bottles. Heck, you can even refer back to this post! Trust us, all your friends at the party will not judge you for using all of your resources while you demonstrate your new trick.

Don’t Forget to Check Back Next Week!

There you have it, Xplorers! Shape, Color, and Finish — those are the first three features of any glass bottle that you can use to identify and find an approximate date for just about any bottle you could find. Archaeologists do it all the time, and now, you can too.

A collection of four glass bottles in different colors

Glass bottles are a unique window into history. Think about how many bottles you have in your home — there are bottles for drinks, bottles for medicine, bottles for cleaning supplies, beauty products, essential oils… some are even just for decoration. Glass bottles have been around for a long time, and they’ve been part of the everyday lives of people like you and us for just as long. Every time we find a new one, we learn a little bit more about the people who used to live here, and what’s more fun or fascinating than that?!

Thank you for hanging out with us and learning a little more about glass bottle analysis today, Xplorers. Remember to come back next week where we’ll round out our discussion of the key features of glass bottles and introduce you (or rather, re-introduce you) to one of our favorites. (Still no spoilers, though!)

Until next time, Xplorers. Keep learning!

— The TerraX Team


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