At Birka last weekend, I got to chat, and pick up supplies from an Aethlemarc soap maker (Mistress Elska), which meant that the bonus day off I gave myself once I was home, I got to play with soap.
I decided to take three plausibly period fats (beef, pork and olive oil), and make soap from each using modern lye to have an idea on how each fat makes soap differ. Most modern soaps are a blend of all sorts of fats, but before I start playing with my own blends, I want to meet each of them individually. Because I’m also entirely too fond of compare and contrast, I also took each batch and split it after I got to trace. One half straight into molds, and the other half got cooked down.

L – R Olive oil, pork, beef. Cold process on top, hot process on the bottom.
I absolutely overcooked the beef tallow soup, I fear I might have undercooked the pork lard soap. I expect the cold process soaps will provide the best comparisons, but I need to wait 3-6 weeks for those to be ready.
The lard soap was /so/ hard to get to trace. I rendered that lard myself, so I do wonder if it’s not quite pure, or something.
Now to wait! All of the soaps will be at Kingdom A&S in March to compare.