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

71–80 of 120 posts

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

#71

Post by celticmusic »

daxorid wrote: post #11

This is interesting, but raises a question. The article mentions: In San Francisco, vault lights are mostly used to illuminate sub-sidewalk basements — ie. basements that extend under the sidewalk. How does this work, legally? Where I live, sidewalks are property of the city (or the HOA, in some cases), and I'd presume the same in SF. Does the title of the sidewalk-adjacent property allow you to excavate N feet beyon…

Property rights don't extend down to the core of the earth unless they're explicit. You have to be careful about this when purchasing land, often times what you're purchasing is the rights down to a certain depth.

A great example of this is oil. When an oil company installs a pump, one of the things they have to do is get agreement from everyone who has mineral rights down to the depths where the oil is. This can get extremely messy, and can often involve people who are not technically the land owners.

I imagine it's a similar situation here, although it could also be that the city simply has an easement on the land itself.

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

#72

Post by BinaryIdiot »

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 you see colored glass, it’s either really old or someone dyed it to mimic the old glass.

So what happens to dyed glass after decades? Does it have a deeper purple? Is it made out of materials that _won't_ change color? Something else?

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

#74

Post by IfOnlyYouKnew »

celticmusic wrote: post #71
daxorid wrote: post #11

This is interesting, but raises a question. The article mentions: In San Francisco, vault lights are mostly used to illuminate sub-sidewalk basements — ie. basements that extend under the sidewalk. How does this work, legally? Where I live, sidewalks are property of the city (or the HOA, in some cases), and I'd presume the same in SF. Does the title of the sidewalk-adjacent property allow you to excavate N feet beyon…

Property rights don't extend down to the core of the earth unless they're explicit. You have to be careful about this when purchasing land, often times what you're purchasing is the rights down to a certain depth. A great example of this is oil. When an oil company installs a pump, one of the things they have to do is get agreement from everyone who has mineral rights down to the depths where the oil is. This can get…

While true, the "certain depth" you speak of is guaranteed to be below the 1" of the article's examples.

But it would be interesting how realistic it is to just excavate from your cellar into other territory. Considering quite a few bank heists have succeeded that way, it might well escape detection for a while.

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

#77

Post by evanthayer »

I restored many old cast iron buildings in NYC that used “bullet glass” paving for the sidewalk above the vault below. These are still manufactured by Circle Redmont (approved by NYC Landmark Preservation Commission) and are beautiful but expensive.

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

#79

Post by inferiorhuman »

chrisseaton wrote: post #62
lqet wrote: post #52

> Vault lights were used to light some of New York City's first subway stations and were placed in the ground of the opulent passenger concourse in the city's original Pennsylvania Station. I will never get my head around the fact that the old Pennsylvania Station was destroyed. It must be one of the biggest mistakes in urban development of the 20th century. > Another architectural critic, Ada Louise Huxtable, wrote…

> the old Pennsylvania Station It wasn't that old! It was only built in 1910, and using modern techniques! It wasn't an ancient monument as you probably think it was, and it was only around for a few decades. Equivalent of a 1960s building being knocked down today.

Equivalent of a 1960s building being knocked down today.

There are plenty of buildings from the 60s I'd be sorry to see go. At the top of the list is the Marin County Civic Center and the TWA Flight Center.

Post reply on HN