The Curly Cooker
 

https://www.sciencenews.org/wp-conte...1981-03-28.jpg

https://www.sciencenews.org/archive/curly-cooker

This article is paywalled, but I've had a photocopy of this magazine cover since the 1980s that just srted to the top of a stack.. The article is paywalled, but everything you need to know is in the cover illustration.

Invented by a high-school student but it never went anywhere (that I'm aware of). So, if you grasp the inner an outer ends of the spiral and twist the spiral springs into a 3D shape. It acts as a 'Fresnel lens'.

At shallow angles it concentrates at a center above the spiral. At steeper angles it focuses behind the spiral.

In a post-apocalyptic scenario this could be valuable information.

Not everything. What is it made of?

I shouldn't speak for others.

Any reflective sheet material. I've been thinking about buying into a local maker-space to get access to a laser cutter. An interesting experiment would be to spring it to a preferred angle and then see if increasing or decreasing the outer radius is called for.

So perhaps polished high nickel stainless of a largish diameter of perhaps 1/4".

That could be tough to extend and retract

...a largish diameter of perhaps 1/4" [thickness]?

As an exemplar, yes. Mylar or aluminum foil would be reflective, it all comes down IMHO to the supporting structure. Maybe 3mm stainless steel? Buffed Polymetal?