This is "old Internet" style fun territory (along the same lines as the Tom7 fun, if not quite as deep). I felt that the olive oil + fingerprint + phone screen was a really nice way to illustrate the core concept. Especially clever because it used something common and annoying to help describe how the plotter does its thing.
Before getting further into the article I thought maybe he was going to show how to use the plotter to control the oil smearing technique, which honestly would have been kind of cool.
He did it on plastic CD cases, not oil. The oil in the beginning of the article was just for explaining the refraction that happens with the ridges in the structure.
It would be interesting to augment the plotter with a Unimorph piezoelectric disk scanner [1], to enable finer movement so lines can be drawn closer together.
William Beaty had a video of the hands on the car hood. They showed up very detailed some 20 cm under the hood as if people captured inside. Quite the find.
Holography is such a beautiful and fascinating gateway to physics, and it’s so rare to see true demonstrations of it. Sadly, most people have no idea what it is because of how carelessly the term is thrown around, just like in this article. At least the author admits it and provides some kind of excuse, even if it’s at the end.
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Maybe could swap out the pen for a needle?
[1] https://john-alexander42.github.io/simple-stm-web-page/Disk_...