Propolis soap

A violin restorer has contacted me looking for raw propolis to use as a ground for violins. Apparently, the story goes something like this:

Back in the days of the old master violin makers, 1550–1730, people who kept bees didn't have the hives we have today. They kept their bees in skeps, baskets woven of straw. Each year, in preparation for the honey run, the beekeeper would clean the hive by leaching it in lye, the result of leaching wood ashes with water. (Today we scrape the propolis from the hive.) The lye would digest the propolis making the hive ready for the bees. This digesting process created a liquid soap from the propolis. It is my belief that this liquid soap was the source of the mysterious ground the violin makers used as an undercoat.

The author gives a recipe for propolis soap and its application here.