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# @CuriousBeing

2025-01-12

Intriguing theory!  Could indeed be the explanation for those "too new" dates.
As for the "too old" dates: gypsum is not a common mineral, so it is likely that the "contractors" who restored the pyramids got some (or most) of it by scraping off the plaster covering of older structures, and baking it again.  Chemically, this recycled plaster would be as good as the one made from freshly mined gypsum.  In fact, the latter may have required extra grinding and purification steps, not to mention transportation; so recycling must have made good economic sense.   Like the recycling of copper, iron, aluminum, and glass today.
In fact, I wonder if this could also explain why the interiors of pyramids are so bare, without any paintings and writings.  Those would normally be applied over a plaster layer...