Little windows into the past

January 19, 2010 5:18 PM

If you live in a sufficiently old city in the U.S.,Canada, or the UK you've probably seen these set into concrete sidewalks or the panels of cast iron steps. Termed vault lights in the U.S., pavement lights in the UK, and sidewalk prisms in Canada, the glass insets were originally clear and intended to produce daylighting in subterranean spaces. The ethereal purple color results from the glass's manganese content being exposed to ultraviolet light over time. Many vault lights or sidewalk prisms are in poor condition, but some are being repaired.
posted by bad grammar (44 comments total)

I'll say that I've never seen these before I came to Vancouver, and that they're really slippery when it rains.
posted by sleslie at 5:24 PM on January 19, 2010

Funny that this shows up here and now. I just learned about these things a month or so ago, from this cartoon by Lucy Knisley.
posted by dlugoczaj at 5:30 PM on January 19, 2010 [4 favorites]

Cool... this is like the antipode of the 1880s-era moonlight towers (you can still see them in Austin TX).
posted by crapmatic at 5:30 PM on January 19, 2010 [1 favorite]

I walk over those Victoria ones all the time -- very cool. I wish they did more special lighting of them from beneath. Great post!
posted by Rumple at 5:32 PM on January 19, 2010

I love these, and I've always wondered about them. Thanks so much.

I knew of a secret old place in my college that was lit only by a few patches of these. I can only hope it's still there.
posted by Countess Elena at 5:36 PM on January 19, 2010

I never knew these existed although I invented them for (basement) offices just last week.
posted by DU at 5:39 PM on January 19, 2010

I returned to San Francisco a couple of months ago and found that when they remodeled the place that the old loos no longer had the vault lights. It was so weird peeing with people walking over you! Kinda missed it.
posted by Ruthless Bunny at 5:39 PM on January 19, 2010

There are quite a few of them here in Melbourne, Australia. I like them.
posted by Joe in Australia at 5:41 PM on January 19, 2010

Lots of old clear glass turned purple from the sun, especially in the Southwestern US. I was told it was because of lead in the glass, but it seems it was Manganese, as you said.
posted by Kirth Gerson at 5:44 PM on January 19, 2010

Are you somehow implying that these things only exist in English-speaking countries? They're everywhere.
posted by effbot at 5:55 PM on January 19, 2010 [1 favorite]

I learned about this on the Seattle Underground Tour, which I can very much recommend.
posted by Morrigan at 5:56 PM on January 19, 2010 [1 favorite]

I'd appreciate anyone's links to the terms for vault lights or pictures in other areas of the world, also where one could collect a single piece. A whole slab would weigh a ton.

I noticed them first in New York City, where I lived for a while (and did a lot of walking), but then I didn't know that the little glass insets were meant to let in significant light. They're usually scuffed and dirty, as the sidewalk photos show. Some cities (such as Victoria, at the link) seem to take more pride in them.
posted by bad grammar at 6:05 PM on January 19, 2010

These are on 14th street just south of Rhode Island Ave in DC (in front of that creepy toy shop that looks like a pedophile's dream bait set-up).
posted by Inspector.Gadget at 6:08 PM on January 19, 2010

I loved these as a kid, but never knew what they were called or what they were for. Thanks.
posted by gamera at 6:09 PM on January 19, 2010

They are pretty common in Brussels, although usually in terrible condition, with many of them missing etc. I shined a flashlight through one of the holes once and it just went down about a foot and met dirt/trash. Maybe the under area got filled in at some point?
posted by skintension at 6:15 PM on January 19, 2010

I had no idea why these were purple!
posted by Sidhedevil at 6:19 PM on January 19, 2010

I had wondered who had chosen purple for so many of these things, and why. Now I know!

Thanks for posting this.
posted by Pecinpah at 6:23 PM on January 19, 2010

Ah, now I know for sure that no one can see up my skirt when I'm walking over these... although in some places, they've been replaced by clear glass so I avoid those unless I'm wearing pants :)

Lots of these up my end of the city (Melbourne). They're lovely, particularly from underneath (there are a couple of basement level restaurants that make use of them).
posted by prettypretty at 6:36 PM on January 19, 2010

The switch from manganese to selenium around 1915 is because Germany and Austria were leading producers of manganese and WW I cut those supplies off, and remaining manganese supplies were in demand for steel making and other industrial processes related to the war.
posted by Rumple at 6:37 PM on January 19, 2010 [2 favorites]

(ooops, pants = trousers! :\)
posted by prettypretty at 6:41 PM on January 19, 2010 [2 favorites]

I have one of these on my mantel right now, salvaged from a sidewalk repair. I've always loved them.
posted by jokeefe at 6:43 PM on January 19, 2010

The nautical equivalent is the deck prism (they make great conversation pieces).
posted by djb at 6:50 PM on January 19, 2010 [1 favorite]

DU, how did you construct these? I've been thinking about something similar for a poorly-lit area under a stairwell (the steps above get direct light), but can't figure out how I'd cut neat square and lipped holes, nor where to get glass to fit.
posted by rokusan at 6:59 PM on January 19, 2010

That is awesome. There are a few around New Haven and some beautiful ones I remember from college (still, ahem, 'in use' by those of us who knew how to get down there.) I never thought to look up what they were called, or followed through on why they were all purple.
posted by cobaltnine at 7:00 PM on January 19, 2010 [1 favorite]

According to my ex-London-bike-messenger mate, these things indicate an area of private property, and are thus a safe place to park one's bike, without fear of tickets (at least in London).
posted by pompomtom at 7:09 PM on January 19, 2010

Got these all over the place in Brisbane, Sydney and Melbourne too.
posted by turgid dahlia at 7:10 PM on January 19, 2010

I used to walk over the ones in Victoria all the time, never knew what they were. I think their are some in Calgary too between 7th and 6th Avenue near the Police station as I vaguely recall seeing them there when switching between the CTrain and the bus.

"DU, how did you construct these? I've been thinking about something similar for a poorly-lit area under a stairwell (the steps above get direct light), but can't figure out how I'd cut neat square and lipped holes, nor where to get glass to fit."

If you don't need it to be water tight a simple sheet of tempered glass, sand blasted wouldn't be slick, bedded in silicone laid down over framing would work. If it needs to be water tight then you'd need to seal the edges some how.
posted by Mitheral at 7:18 PM on January 19, 2010

prettypretty wrote: "Lots of these up my end of the city (Melbourne). They're lovely, particularly from underneath (there are a couple of basement level restaurants that make use of them)."

I was just going to mention how a restaurant in Fayetteville, Arkansas, USA, named Hugo's (click the link and look at the top picture to see them from underneath, at a very poor and unimpressive angle, anyway) has these. They're in the basement of the building where my boss keeps an office.

I've walked over them a gajillion times and never had a name for them.

Either the building was built late enough or the awning over the vault area shades it enough that they have yet to turn purple. I know it was built in the 10s, but the contrast on the google street view image is bad enough that I can't make out the writing on date block.
posted by wierdo at 7:41 PM on January 19, 2010

These remind me of the lights (with lightbulbs) in the doorways of many London restuarants/clubs I saw there. Are they a stylistic relative, perhaps? These were right on the threshold and would be lit up different colors.

(we have an extensive tunnel system on my uni campus; I wish they would've used these instead of the strands of tunnel lights on extension cords and metal grates)
posted by rubah at 7:50 PM on January 19, 2010

Thank you so much! I was actually walking along the street in Portland a couple of months ago and passed over one of these and wondered to myself:
"Why are these here? Is it a decorative thing? And why Purple?"
posted by kaiseki at 7:56 PM on January 19, 2010

I'd appreciate anyone's links to the terms for vault lights

A Swedish encyclopedia from the early 20th century calls them trottoarglas (pavement glass), and also mentions "Luxfer" as a modern brand.

In more modern use, they're probably just considered an early form of "glasbetong" (concrete glass) or just "glasblock" (glass blocks).
posted by effbot at 8:01 PM on January 19, 2010

I imagine that glass bricks would work for this, if set in a proper frame. But I'm sure Owens_Corning could tell you for sure.
posted by msalt at 8:19 PM on January 19, 2010

I remember going on an underground tour of Vancouver's Gastown when I was a kid way back when and we'd see all these glass blocks from underground. Unfortunately, I think many of the tunnels in Chinatown and Gastown are blocked up now, and the vault lights are covered up in most places.
posted by Extopalopaketle at 8:31 PM on January 19, 2010

Neat, I suppose these are the future of this technology?
posted by jkaczor at 8:33 PM on January 19, 2010

Old glass in general has this violet color to it. I remember as a kid, we had a few kerosene lamps that had turned violet. My mom said they were valuable. Of course, they've gone who knows where.
posted by eltopo at 9:24 PM on January 19, 2010

Electric pole glass insulators that are "sun-colored amethyst" are quite valuable.
posted by dw at 9:56 PM on January 19, 2010

Great post! I always assumed these were merely decorative.
posted by serazin at 10:15 PM on January 19, 2010

I love these. They remind me of Vancouver--they're everywhere there, or used to be; I think I remember asking my dad about them when I was a kid and being surprised about the underground walkways.

Like you, prettypretty, I always avoided walking over them if I was wearing a skirt!
posted by hurdy gurdy girl at 11:54 PM on January 19, 2010

They were also used as ventilation in case of basement fire - the idea being that the fire brigade would knock out the glass with pickaxes, or lift the whole unit open to enable smoke to leave.

(I don't think this method is current practice)
posted by Kiwi at 2:15 AM on January 20, 2010

Paul Collins: Cutting energy bills the Victorian way.
posted by user92371 at 3:57 AM on January 20, 2010

Strange... I too had wondered about the color, but most of the links I've seen here don't match my experience - The "purple" in the linked pics looks like a very faint discoloration, visible but subtle.

I have a pair of these, from the roof/ceiling of an old (pre WWI-era?) military observation tower that had crumbled to rubble, and their color has nothing subtle about it - They look dark frickin' violet.

Of course, they also differ in shape from every example I've seen so far - Round Instead of square or triangular, with a flat top and smoothly concave bottom, and the hint of threading around the outer rim (or perhaps just a mortar groove - pretty badly beaten up, hard to tell). So perhaps not the same thing, but definitely intended for the same purpose.
posted by pla at 6:48 AM on January 20, 2010

Sorry for the derail, but I had to chuckle at this quote in the "daylighting" link:

In February 1904, The New York Times noted that ''a speck of dirt would find a difficult resting place'' in the new subway stations

NYT: Getting it ridiculously wrong at least since 1904.
posted by Skeptic at 7:31 AM on January 20, 2010 [1 favorite]

They have these in Pendleton, OR. On the Pendleton Underground tour, they point out that they are the way the old opium dens, prohibition time saloons and gambling rooms and secret passageways to the brothels were lit. Quite fascinating. Kind of creepy from down below since everything has a purple cast and is still quite dark.
posted by Jenny is Crafty at 12:30 PM on January 20, 2010

DU, how did you construct these? I've been thinking about something similar for a poorly-lit area under a stairwell (the steps above get direct light), but can't figure out how I'd cut neat square and lipped holes, nor where to gt glass to fit.

you can make them yourself by using clear fusible glass and a ceramic mold. It just has to be a tapered cube. Also, you probably want to use a low COE glass (88 or lower) if it will be for architectural uses.
posted by yesster at 8:08 PM on January 20, 2010