Do you use or have any data on these recent formulations?
If you are referring to some of the latest soap bases, such as Milksteak, Siero, or Soft Heart Series, I have tracked them, as well (for the short while that I’ve used them). I’ll do bullet points again for clarity.
• I use natural hair
and synthetic brushes. (Mostly badger, though.)
• Knot sizes vary between 24–30 mm. (Most often 26 mm.)
• I always use close to the same amount of soap, regardless of the type of brush.
• The tap water here is hard, but runs through a softener.
• I only do two-pass shaves.
With all of those soap bases, I can get a decent two-pass shave with 1.5 grams of soap, but I much prefer to use around 2 grams, as it improves the quality of the lather. I load the soaps from a steel bowl with a brush that has been squeezed fairly dry. While I eventually do add a few drops of water to the bowl, developing the lather continues on the face. I like to aim for a fairly shiny lather, but not one that is drippy.