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Comment by hfsh | Hacker News Reader

I mean, even then you're growing it from chemicals. Unless you're straight up converting energy to matter (in which case, it would be kind of odd the first practical application they think of is making colors).

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In the sense that everything is chemicals, yes. But you typically wouldn't describe a butterfly growing a wing or a welder making a blue weld from metals that are normally very much not blue as "growing from chemicals". I guess you could argue about the butterfly, but I think few people would say that chemicals are involved in welding steel, despite iron, carbon and tungsten being chemical elements

The few people that would say that chemistry is part of welding "steel" (what type of steel? what type of metal? how about aluminium? etc) includes welders.

eg: https://youtu.be/nfNvuTMDXNg?t=1420

In which a good machinist from Queensland, Australia discovers a crack and states he'll have to get the metal tested before he can repair the crack.

You know, to match the chemical composition, expansion rates, etc.

Well, the counterargument is that in theory, you can imagine a way to create structural color regardless of substrate. So imagine a technology that shines a laser on a car or a block of concrete and makes it blue; I'd argue that's correctly "without chemicals".

Of course, I doubt you can do that to any random substrate, since the color will depend on the properties of the material.

  So imagine a technology that shines a laser on a car or a block of concrete and makes it blue

There is something like that for sheets of steel at least https://www.youtube.com/watch?v=2ncEfAxkuFA

And here is a video explains it https://www.youtube.com/watch?v=RsGHr7dXLuI

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