Forgotten knowledge, methods, technology, etc.

[billfish678]

@jackdavinci

I read something to the effect of, if you move the stone back and forth in place, it naturally smooths away any imperfections in fit.

If you have 3 surfaces and you alternate which ones you grind against which you automatically get a flat surface. And with a little care and eventually getting to very fine grit it will be VERY flat. Like a tiny fraction of the size of the finest grit you used flat. This is telescope optics making 101 where you eventually get to optical flats that are fraction of wavelength of light flat. And this can be done just by hand with eyeballs and some knowledge of optics and simple equipment. Not that those guys went to that level. Just noting that some amazing things can sometimes be done with just a little bit of the right knowledge.

[Chronos]

Quoth si_blakely:

Sometimes it is not what has been forgotten, but what was not known in the first place.
FOGBANK is a foam material used in thermonuclear warheads. Production was stopped in 1989, and production lines decommissioned. When a warhead refurbishment program was instituted in 2000, production of FOGBANK was restarted. It took until 2009 for useful material to be produced. Not only were records and details lost, modern raw materials were much more refined than original feedstocks, and a contaminant in the original raw material proved to have a vital role in the correct production of FOGBANK material.

It took 11 years for that knowledge to be lost, and 9 years to be recovered.

Si

As I understand it, the situation with Damascus steel is similar: The actual techniques weren’t all that complicated, it’s just that the ore used in Damascus, unbeknownst to anyone, had traces of (I think) vanadium, which turned out to be critical.

[Tastes_of_Chocolate]

@gotpasswords

For the time being, the precise technology, chemistry and process needed to make a good replica of Polaroid film has been lost.

@Machine_Elf

Has it in fact been truly lost - that is, no one alive knows exactly how to do it, and all written records of how to do it have been destroyed? Or does the Polaroid company still have detailed documents about the ingredients and process, but they’ve chosen not to reveal them to anyone else?

Or is it just not worth the money to make the film the same way. If the original production required a specific machine or material, and it’s not worth the cost to reproduce that machine or material, then the technique isn’t really lost, it’s just not being used.

I bet I would create, with no modern tools, a seam between 2 rocks that was extraordinarily precise. It would take lots of time and effort, and personally, I’d rather go buy 2 bricks and slather mortar inbetween. So while I could do it, I’m not going to; it’s not worth the time or the money.