A few years ago I stumbled across two recipes in the Trotula (https://www.pennpress.org/9780812235890/the-trotula/) that are for treating sunburn/windburn, but at the end they say they are also good for prevention of the same. As a Translucent American with sensitive skin, I was intrigued by the idea of a period-appropriate sunscreen. My research and understanding have grown a lot over the last few years.
Here is a link to my first presentation: https://athenaeum.baronyofmadrone.net/exhibits/against-sunburn/
my paper for the 2024 Kingdom competition: AN 11TH CENTURY ITALIAN SUNSCREEN
Since then I have looked further into similar creams and discovered that tin oxide was often used interchangeably with white lead and zinc oxide – I acquired some white lead to do a test batch (yay toxins!) but it’s proving to be difficult to get tin oxide in less-than-industrial amounts.
In my totally non-modern-scientific experiments I can report that the cream as I made it is VERY effective at preventing sunburn. It is functional for about 24 hours in high heat (lots of sweat). I tried using coconut oil to make a vegan version and sadly the coconut smell was overpowering. Crisco did the job fairly well. I did a few batches with tallow I rendered myself but I have a hard time filtering the oil enough to get rid of the cow smell so I use commercially available lard when I make it for gifting.