That example feels strangely specific ;)

This is one specific type of sensor. There are a lot of different types of ultra-sensitive magnetic field sensors, and while specific manufacturing knowledge might die, documents describing how the devices work will persist.

Example: https://pmc.ncbi.nlm.nih.gov/articles/PMC7146409/

Utterly irrelevant to the discussion

What an arrogant and rude comment.

Is there a particular reason you think it's irrelevant to have documentation on how to build something that might become uneconomical to build to the point of losing the technology? Or are you just being an asshole?

oh wow someone being terminally online

My broader point is not about any one part or process, but rather that every big mass-market technology that dies out in favor of something new (hard drives, film cameras, casette tapes, incandescent lights, vacuum tubes, etc) also takes down dozens of niche industries that had sprung up around that technology's economies of scale, and which are not economical to continue when it winds down. While the original product might be obsolete, these smaller industries are often producing something completely different and just happen to be sharing some element of the supply chain, but they're not big enough to sustain that supply chain on their own. Sometimes they might be able to substitute something else at a small loss, sometimes they can purchase the last remaining inventory of the closing factories and survive on that for a decade or two, but there are cases where a technology just disappears, never to be recreated.

Written documentation almost never captures the complete details needed to produce a complex technology, and outside of extremely vertically-integrated industries, such documentation would rarely exist in one place anyway. You're lucky enough to find detailed documentation from the source company that makes the sensor/widget, but even so a document that opens with "step 1: purchase alloy #755-D from Westchester Special Metals, hydrogen annealed" is not much help if Westchester Special Metals went out of business 60 years ago, and had the usual number of trade secrets.

I understand your point. However I think that in practice it's more likely to play out like the Greek Fire example in the article. That is, no we can't precisely replicate it, but it doesn't matter because we have napalm. Greek Fire specifically is unnecessary, since we can meet or exceed the spec with things we can make.

There are many different types of ultra-accurate magnetometer. They are made in many different ways. If one relies on some byproduct of some other industry that goes under and becomes nonviable, then the many competitors will fill the niche with a different type of magnetometer that will be just as good.

Even if we consider a different hypothetical industry that truly is single point of failure, well, there are academic papers explaining how these things work and how to make them. Maybe the specific model of metal is no longer made, but the instructions there and an intelligent, motivated person will figure it out. And then they'll figure out how to improve it.

I don't think the failure mechanism you describe will in practice lead to anything more than brief gaps in the availability of a technology. We can remake things to spec, like FOGBANK.

That kind of reconstruction effort only happens with a huge budget, which means for most of these technologies, it never happens at all. Academic papers only give a basic starting point; especially for materials science, people dedicate the span of their entire years to developing manufacturing processes beyond what ever gets published in public. With enough motivation you can have the pleasure of following their footsteps, but it will consume more than one lifetime to do so. And nobody will fund that rediscovery effort, because there's no money in niche industries.

A result of this is that, in some rare cases, there are certain machines and instruments where the best ones in existence were manufactured in the '80s and are jealousy hoarded in temperature-controlled vaults, because nobody today can make a better one and the industry that produced them is completely gone.

FOGBANK is a great example of a lost technology that had to be rediscovered at great expense, and that only happened because the military could write a blank cheque. But that's exactly a lost technology; they had to do the R&D all over again. And even then, they didn't have to make up for a bigger market that vanished; they were always the only customer for FOGBANK, so the economics hadn't changed. Imagine if the economically producing that material required a customer base the size of Kodak's peak market share to amortize the capital cost of a production run.

Most technologies don't have infinite money available to recreate from scratch; they depend on economies of scale and die out with their markets.

Which "cases where a technology just disappears, never to be recreated" are you thinking of specifically? I'm persuaded by your logic that this must be happening, but I'd like to know what it looks like in practice.