Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

What are those grids of glass in the sidewalk and why are they purple?

kqed.org

Post reply on HN
Print view View original

101–110 of 120 posts

Re: What are those grids of glass in the sidewalk and why are they purple?

#101

Post by Cougher »

subroutine wrote: post #97
Cougher wrote: post #95

Earlier quoted context omitted.

"Equivalent of a 1960s building being knocked down today." I feel like you refuted your first sentence with this!

A 1960s building is old, but 80 years isn't really enough to inspire awe; there are plenty of existing structures several hundred to several thousands of years old. https://en.m.wikipedia.org/wiki/List_of_oldest_known_survivi...

"A 1960s building is old, but 80 years isn't really enough to inspire awe;"

That's absolutely untrue. Plenty of buildings inspire awe immediately upon completion and plenty of them have gone through their entire life-cycle within a span of 60 years. Try Quarry Hill Flats for a start. https://duckduckgo.com/?q=quarry+hill+%2Bflats&t=opera&ia=im...

"there are plenty of existing structures several hundred to several thousands of years old."

This is a bizarrely obvious statement, like, who doesn't know this?

Re: What are those grids of glass in the sidewalk and why are they purple?

#102

Post by Symbiote »

lgeorget wrote: post #53
Angostura wrote: post #49

Lots in London, and many very old - but I've never spotted purple ones.

Well, the color being due to exposition of the prisms to UV radiation, it will take a lot longer to reach the purple tint in London than in California.

It's more likely that British glass manufacturers used a different chemical.

Re: What are those grids of glass in the sidewalk and why are they purple?

#103

Post by jaclaz »

oneeyedpigeon wrote: post #55
robk wrote: post #7

These are ubiquitous in London

Notably the ones in Crystal Palace [1] which are above an old underground toilet, now converted into someone's house! [2] I guess — in this case, at least — the fogging-up of the glass is actually a privacy feature. [1] http://1.bp.blogspot.com/-SuRJ4LN5LhQ/T3GQS8rUN9I/AAAAAAAAAM... [2] http://crystalpalacetoilets.blogspot.com/

Only for the record, there is a "modern" material, called "glass block" since the '50's or '60's, the one in your photos seem like it (and there is no "prism" like the kind described in the main article) that can be used also for walls.

Example:

https://www.sevesglassblock.com/wp-content/uploads/2018/03/T...

(go to page 54 of the .pdf)

Re: What are those grids of glass in the sidewalk and why are they purple?

#104

Post by jacquesm »

Cougher wrote: post #96
ehnto wrote: post #90

Earlier quoted context omitted.

Lost craftsmanship and cost of construction has risen so much that some projects just couldn't be afforded anymore. My city once had an extensive rail network, it was torn out in favour of cars. Now that we want to put it back in, construction costs are so inflated we can't afford it.

If it's in America, it isn't a matter of not being able to afford it; we choose not to, instead prefering to waste it on military spending. Our country really could be great again if we chose to stop that madness.

You're about to engage in several major public works worth of military spending.

Re: What are those grids of glass in the sidewalk and why are they purple?

#105

Post by jacquesm »

Piskvorrr wrote: post #99
BinaryIdiot wrote: post #72

This is fascinating. I've walked over those countless times and always wondered what they were. I am curious about this one bit though: > When vault lights were first installed, much of the glass was clear. But when the manganese is exposed to UV rays for long periods of time, it photo-oxidizes and turns purple or pinkish. Hence, the reason so much of the glass is now purple. > This process can take decades. So when…

Perhaps any of these, depending on the materials. Color stability in the long run is rarely a concern.

That depends on the application. In stained glass and other glass used for art color stability is very important in the long run.

Re: What are those grids of glass in the sidewalk and why are they purple?

#106

Post by barrkel »

subroutine wrote: post #97
Cougher wrote: post #95

Earlier quoted context omitted.

"Equivalent of a 1960s building being knocked down today." I feel like you refuted your first sentence with this!

A 1960s building is old, but 80 years isn't really enough to inspire awe; there are plenty of existing structures several hundred to several thousands of years old. https://en.m.wikipedia.org/wiki/List_of_oldest_known_survivi...

Age isn't what inspires the awe, though.

Re: What are those grids of glass in the sidewalk and why are they purple?

#107

Post by tialaramex »

Cougher wrote: post #101
subroutine wrote: post #97

Earlier quoted context omitted.

A 1960s building is old, but 80 years isn't really enough to inspire awe; there are plenty of existing structures several hundred to several thousands of years old. https://en.m.wikipedia.org/wiki/List_of_oldest_known_survivi...

"A 1960s building is old, but 80 years isn't really enough to inspire awe;" That's absolutely untrue. Plenty of buildings inspire awe immediately upon completion and plenty of them have gone through their entire life-cycle within a span of 60 years. Try Quarry Hill Flats for a start. https://duckduckgo.com/?q=quarry+hill+%2Bflats&t=opera&ia=im... "there are plenty of existing structures several hundred to several tho…

Also, we're not just talking about a "structure" like the pyramids or various ancient monuments, Penn Station had an _function_ it was needed for.

Not many "several thousand year old" structures with a function exist except as museums now. There's a house somewhere that's been continuously inhabited for about a thousand years (Faroes maybe?) and a few of the forts or religious buildings still in use are older, but most structures this old are, like the pyramids, just a tourist attraction now. New York did not need another museum, it needed a railway station.

Re: What are those grids of glass in the sidewalk and why are they purple?

#109

Post by eskaytwo »

jdnenej wrote: post #92
BinaryIdiot wrote: post #72

This is fascinating. I've walked over those countless times and always wondered what they were. I am curious about this one bit though: > When vault lights were first installed, much of the glass was clear. But when the manganese is exposed to UV rays for long periods of time, it photo-oxidizes and turns purple or pinkish. Hence, the reason so much of the glass is now purple. > This process can take decades. So when…

I had no idea these were an actual thing. I just figured it was some whacky street decoration. The ones in Adelaide, Australia are mostly cracked and ruined and seem to be filled in with concrete when they break. I wonder if everyone decided it's easier to use electricity for lighting now.

Where are they in Adelaide?

Re: What are those grids of glass in the sidewalk and why are they purple?

#110

Post by tehwalrus »

Piskvorrr wrote: post #98
blntechie wrote: post #93

Earlier quoted context omitted.

When I first learned about raising the streets at massive scale in American cities (Chicago Seattle etc.), I was very fascinated. I’m not sure if this is/was an unique American exercise.

Medieval cities used to do this; essentialy a transition from a small town to an actual city, i.e. "we are no longer able to fit the place to nature, let's do the opposite thing then."

See also Rome, which is built on top of about eight more layers of Rome. Residents often get architectural and history students asking to look at something weird in the basement.
Post reply on HN