Study of a triangular bottle
We acquired this small blue glass bottle nearly 15 years ago, as a prop for a Harry Potter themed birthday party. For much of the time since then it’s been decorating our bathroom window with several other blue bottles. Like most bottles these days, it’s molded rather than blown, but a little roughly so the welding seams are more visible than they usually are on wine or liquor bottles.
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As you can see, it has an unusual triangular cross-section. The final image, with a Reuleaux triangle overlaid, shows that the curvature of this cross-section is less than a Reuleaux triangle would have. I don’t think its outline was chosen with any particular mathematics in mind, but only (as so many other curved triangles) to make an interesting shape.