The Aztlan collection are a group of artifacts allegedly ancient which depict paleocontact between aliens and humans. There's a number of claims around them, mostly as a result of independent researcher Trevor Hawke who purports to have evidence they're genuine. Here's his paper: https://www.academia.edu/167025997/Prehistoric_artifacts_of_Mesoamerica_anthropological_evidence_of_ET_paleocontact Here's a paper that alleges all his research methodology is poor and doesn't prove his conclusions:...

This is an actual thorough paper. The technique to how they did this low temperature cure is unknown to us. https://www.academia.edu/167025997/Prehistoric_artifacts_of_Mesoamerica_anthropological_evidence_of_ET_paleocontact Conclusion The multi-analytical investigation of the Aztlan collection, an assemblage of over 10,000 specimens from the southern highlands of Jalisco, Mexico, presents a significant challenge to traditionally established anthropological and archaeological timelines. The co...