Title: Metal marbles.
Summary: Introduction of host, with reference to semantic playgrounds.
Link to the rust converter recipe, which I found to be cheaper, and more sprayable than buckets of gel or paint-like substances which you might find elsewhere:
https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/tannic-acid-rusted-iron-artifacts.html
In case that link moves, search for tannic acid rust converters, then choose your buffers.
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Mastodon, though very very rarely: