Pouring the 200 inch disk at Corning Glass Works
nyheritage.org
nyheritage.org
Video of the pouring process: https://www.youtube.com/watch?v=KdqaC8pLixY&t=15s
Transport: https://sites.astro.caltech.edu/palomar/media/slideshows/mir...
Polishing: https://sites.astro.caltech.edu/palomar/about/telescopes/ima...
Click the slideshow and press the left/right arrows to advance the slides or go back.
It seems like the first mirror cracked, so they manufactured a second mirror in Corning, New York (taking 10 months to cool it down and anneal it after it was poured), moved it across the country to Caltech in Pasadena, then they spent 11.5 years polishing it down to 14.5 tons... wow! And finally trucked it over to its current location in the Palomar Observatory in San Diego. I can't imagine being the crane operator while loading and unloading this thing.
wow, talk about a long-term project
Firebrick bolted to the base of the mold to form the void spaces broke loose and floated to the top of the mirror blank.
I did some consulting for Corning back in the late 2000s and took an afternoon to visit the museum. I can't recommend it enough.
Corning is an exceptional company and so much of our technology, from fiber-optics to monitors and screens to Gorilla Glass, is thanks to the brilliant minds at work there.
After the fiber optics, they repeated the performance with the Gorilla Glass. See, we don’t understand it anymore today but having glass screens on “smartphones” was a revolution - we didn’t do touchscreens earlier because screens were plastic, like in the Palm Pilot; they were plastic because people pushed insensitively, people did that because the touch wasn’t sensitive at all (cursor would always land at the wrong place, or not be sensed at all).
What Corning built for Apple was a glass screen, almost unbreakable, and thin enough to have an amazing touch resolution.
https://www.fastcompany.com/40493737/how-cornings-crash-proj...
Along those lines I highly recommend the episode of the show “How we Got to Now” about glass [0]. It tells the story of how clear glass was developed, something I always took for granted, but early glass was not clear and took a major effort to create. The show then goes into how Corning took it to a new level for fiber optics. The whole series is excellent and similar to James Burke’s excellent series “Connections”. [1]
[0] https://www.imdb.com/title/tt4160136/
[1] https://www.imdb.com/title/tt0078588/
[1] https://www.youtube.com/watch?v=XetplHcM7aQ&list=PLf02uWXhaG...
I also like that they pressed on with annealing the first cast even though it was a reject. Avoid the unknown when you repeat for the final one.
There's a blog post I can't find any more about a camera nut visiting one of the last Japanese refactories capable of making lenses and the excruciating processes they go through to make complex zonally variant glass. Mirrors seem almost simple by comparison.
I mean, assuming the glass starts at like 1000 degs, (I have no idea) that means cooling about 2.5 degrees per day. Which I assume means inside an active furnace.
The additional energy, and hence cost of the finished glass but have been massive.
Presumably they learned this would be necessary from the test piece, which presumably cracked at some point.
It's relevant to remember that this is a gradient tempreture throughout the mass that declines and not a uniform fall throughout.
An analog might be to think of a porous spongy material (clay, heavy peat moss, etc) and water .. annealing is the process of slowly leaching out the tempreture (or water) with no abrupt gradient changes that lead to cracking.
As the temp. in the annealing furnace is staged down, there must be a pause to allow the heat to flow out from the mass centre to match the furnace before the next reduction.
> Which I assume means inside an active furnace.
Ideally a very well insulated furnace so that little energy input is required to maintain the desired furnace mean.
Was it this one?
https://www.imaging-resource.com/news/2018/04/17/glass-for-g...
If only we did this for software instead of just keeping the reject.
Two standout passages for me are the construction of the parabolic primary (by the end they were polishing it with the ball of their thumb, knowing how much glass each pass would wipe off), and the support mechanisms that account for flexing in the mirror, which sound like absolute black magic to someone trained on digital systems.
As another commenter has already mentioned, there really is something to be said for a business picking one thing- just a single specialty- and doing it really d**ned well.
Maybe Corning can give me some pointers on how to get a modest 3'x3' piece of glass for my coffee table back from my local home improvement store without having it shatter into a million pieces...
Simple, hire having it delivered. People who deal with decent-sized chunks of glass or other brittle materials like stone countertops have vehicles with structures built to support what's being transported safely. For a 3x3 piece, a rack in the back of a pickup truck would likely work fine, if it was a larger tabletop then a glass contractor vehicle with a larger carrying space on the side would be needed.
A thicker piece of glass might also work better.
That is how you accelerate learning anything. In a large multi-stage, multi-disciplinary project, there is always a temptation to give up and start over the first time a stage fails.
But that means you always enter new stages with perfect inputs and no experience. Way better to keep working on flawed WIP to build experience and test new processes with lower stakes.
https://www.lickobservatory.org/explore/36-inch-lick-refract...
The lens was built in France in the 1880s and transported to San Jose. I don't know about COVID closures now, but I looked through it in the early 00's.
They used to do campouts for students - it was a 6th grade trip.
Looks like it's closed for Covid for now.
It’s truly time to let covid fears subside and fade away.
I’m much more concerned with irrational people who get angry with someone not wearing a mask than I am that the person not wearing a mask would be a risk to me.
Of course, and thankfully unhinged zealots are a small percentage of potential visitors. Still, my point is that it's hard to blame institutions that aren't mandated to have public access for avoiding the entire issue.
They pour somewhat larger mirrors - most recent ones are 8.4 meters (330 inches) for the Giant Magellan Telescope.
There are some other videos shot in the pandemic--it's a bit of good fortune that safety controls against silicosis are also super effective against respiratory pathogens.