Just because you probably shouldn’t make a DIY X-ray machine, doesn’t mean nobody would. [mircemk] shows off his DIY unit, how it works, how to use it safely and of course, some pretty X-ray photos of household objects.
The machine repurposes a DY86 vacuum tube from old CRT TVs to emit X-ray radiation. To drive the tube without blowing it up, a rather specialized series of power supplies is needed; a low-voltage DC power supply powers a high-voltage AC inverter, which is then sent through first a transformer, and then a Crockfort-Walton voltage multiplier, to reach the incredibly high voltages needed for such a vacuum tube’s radiation emission to reach X-rays. Naturally, this didn’t go to plan first try, leading to the unfortunate demise of three vacuum tubes (as well as another three which had already lost their vacuums).
Now how do you capture an image with X-rays for a light source? With dental X-ray photo films of course! The dental film is placed behind the object to be scanned, the transmitted X-rays making up the resulting image. After going through the standard process of developing for about 30s, washing, fixing for about half an hour, and washing again, the photos become clearly visible. The best results were obtained at a distance of 10-15 cm an an exposure time varying from 15 minutes to an hour depending on material hardness.

That’s “Cockcroft-Walton voltage multiplier”:
https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator
Even the video got it right.
It depends on material density and the type of material, not hardness.
X-ray diffraction can be used to determine the hardness of hardened steel, but that’s not what this project does:
https://dl.astm.org/jte/article-abstract/12/1/13/17580/An-Estimation-of-Hardness-of-Hardened-Steels-by-X?redirectedFrom=fulltext
X-ray film is available in larger sheets, if desired. A considerable number of people with large format cameras have been experimenting with using it, since it is in some ways closer to the films that would have been used in those cameras when they were first sold and it is relatively easily purchased and cut to size.