I found this glass on the beach on Prince Edward Island.
April 16, 2018 1:51 PM   Subscribe

In what is probably the biggest hunk of beach glass ever... I found this on the shore on PEI two Summers ago. Pic 1, Pic 2.

It's heavy, and thick, and kind of roundish, but as you can see broken.

I was thinking some kind of electrical insulator, or maybe a submarine window.

Does this look like a broken part of a thing, or maybe just a large hunk of glass found on the beach?
posted by bricksNmortar to Science & Nature (22 answers total) 2 users marked this as a favorite
Maybe part of a Fresnel lens, from a lighthouse?
posted by The otter lady at 2:12 PM on April 16, 2018 [1 favorite]

Is it translucent? It looks green, is that accurate? If it really is green I'd say it's the lens of a (big) ship's starboard running light.

It's hard to tell if the concentric rings are part of the piece's original shape or an artifact of whatever damaged it. Ship's lanterns are historically curved, but there's very little to go off of here.
posted by Mr.Encyclopedia at 2:31 PM on April 16, 2018

To my eye that looks very much like a chunk of slag glass from a factory. If there was ever a glassworks nearby that produced colored fishing floats or the like, I'd guess it's from their furnaces.
posted by DSime at 3:17 PM on April 16, 2018 [4 favorites]

Yes looks like slag to me as well.
posted by carter at 4:16 PM on April 16, 2018

What color is it? It looks black to me. So the bottom of a big bottle or jar, ballast, or slag. Now I know what slag glass is!
posted by vrakatar at 4:41 PM on April 16, 2018 [1 favorite]

It's grey, and not terribly translucent.

I've seen slag glass before and it's usually very irregular.

Though rough, it seems like this was a finished.piece, roundsh, flat and thick.
posted by bricksNmortar at 4:47 PM on April 16, 2018

Not to me. Another vote for slag. Certainly not a Fresnel lens -- those grooves are too irregular.
posted by Rash at 5:06 PM on April 16, 2018 [2 favorites]

Slag glass I've seen fractures more chaotically because it's cooled too fast. You're 100% sure it's glass? No chance it's a piece of flint left behind by glaciers?
posted by bonobothegreat at 5:17 PM on April 16, 2018 [2 favorites]

Not a lens or window, but why not a broken thick bottom of a big ol’ 10 gallon jug or similar?
posted by SaltySalticid at 7:21 PM on April 16, 2018 [2 favorites]

I'm not yet convinced it's man-made. May I see pics of the roundest edge and the other side? Looks to me like it could be obsidian.
posted by at at 8:36 PM on April 16, 2018 [3 favorites]

yea, I was also going to say obsidian
posted by 5_13_23_42_69_666 at 9:01 PM on April 16, 2018

Looks to me like it might be chert. It is a sedimentary rock of microcrystalline silica.

You can see an outcropping and similar pieces broken off in this picture.

Chert tends to break with conchoidal (circular) fractures.
posted by JackFlash at 9:36 PM on April 16, 2018 [4 favorites]

It's definitely glass. I'll post some new pics later today or tomorrow.

I'm going with submarine window until we can figure this out for sure.
posted by bricksNmortar at 5:10 AM on April 17, 2018

Just to rule a couple of things out, from a public historian with some maritime training
-it's definitely not a Fresnel lens
-it's definitely not a ship running light
posted by Miko at 5:43 AM on April 17, 2018

Just to rule a couple of things out, from a public historian with some maritime training
-it's definitely not a Fresnel lens
-it's definitely not a ship running light

posted by bricksNmortar at 6:07 AM on April 17, 2018

Based on JackFlash's links, I vote for obsidian.
posted by Thorzdad at 6:48 AM on April 17, 2018

I'm going with submarine window

The thing about windows is that generally you're supposed to be able to see through them.

I can't see the stuff behind the glass in your photos.
posted by flabdablet at 10:08 AM on April 17, 2018

The piece looks extremely porous; seems unlikely to be any sort of window or piece of a vessel for storing liquids.
posted by Mitheral at 8:14 PM on April 17, 2018

I'm an archaeologist. I don't think that's obsidian. I'd be astonished in fact if it were. For one thing, I don't know of any obsidian sources within several thousand kilometres of PEI. While there is conchoidal fracture around the edge of the piece, this is as likely to happen with glass as it is with obsidian or chert. The circular rings on the face do not appear to me to be caused by conchoidal fracture. The way they terminate on the face with a mixture of smooth and very sharp, steep rings is not typical - also how some rings converge and almost cross each other.

I think it's more likely to be glass, and that area is part of the manufacturing process. I suspect it is part of a very large glass fishing float, which normally have a circular area like this on them. Furthermore, this is the thickest area on a float and the most likely to survive. It is a very typical colour for a glass float. And, a fishing float is much more likely to end up on a random PEI beach than a lighthouse lens (a zebra, not a horse, so to speak) or a submarine window (a quagga).

While glass fishing floats are most commonly associated with Japanese/Pacific fishing practices they were in use in the Atlantic since the early 19th century as well.

Here's a large glass float the size of a basketball. I don't see any obvious reason why this isn't compatible with what you found and contextually it is the most likely.
posted by Rumple at 11:38 PM on April 17, 2018 [4 favorites]

As promised, more pics. I cleaned it up a bit and took some pics to show how transparent it is.

Pic 3 This one shows the best view of what appears to be the only intact "finished" edge of the glass and highlights it's translucence / transparency. The edge looks curved, but it's actually straight.

Pic 4 Here it is on a kitchen scale weighing in at 2 lbs 5.3 oz. Also shows the "finished" edge.

Pic 5 Not the best angle, but another view of the finished edge.

At this point, I'm thinking it's a fragment of what was a large and thick piece of glass that had at least one straight edge. I likely maritime in nature as there was both flotsam and jetsam all over the beach at PEI.
posted by bricksNmortar at 5:03 AM on April 19, 2018

The extra pictures really help. My guess would be it's the bottom of a large glass jug or jar. There looks to be a central raised layer that would match the indentation on the bottom of large water jugs and storage jars that facilitates rolling and grasping. The other lines and nicks would just be impact fractures. See this for the kind of thing I mean, though the scale of yours looks much bigger. More on bottle bases here.

It's quite possible it was clear once. Old glass can change color due to solarization.

It really doesn't have any features that suggest a nautical application. Too shapeless for a deck light, too flat for a running light, too big and heavy for much else. If it did come off a boat, its likely function was food or water storage.
posted by Miko at 10:04 AM on April 19, 2018

If that is a finished edge then I doubt it could be a fishing float. However I'm not sure it is a finished edge. There's at least one chip taken off which is the same texture and appearance as that edge. There's no sign of finishing per se, it just ends like a sheet of plain window glass, whereas something like this, unless it was indeed a (very crude, uneven, dim) window, I would expect it to have some kind of lip or trough effect along there. So I would maintain my fishing float guess for the time being. If it's not finished then Miko's suggestion of the base of a large bottle/jar bottom would also be possible

The circular/curving ridge which appears to be about an inch inwards of the "finished edge" in Pic 4 looks interesting and probably manufactured?

If it is a real finished edge, then I might consider a remnant of a large, rectangular battery case (wet cell). However it seems a little crude and uneven for that application.
posted by Rumple at 11:13 AM on April 19, 2018

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