Here is an old recipe from Millard Buchanan. Foxfire 2 1973

Use five pounds of grease, one box Red Devil Lye, three tablespoons of borax, two tablespoons of sugar, one tablespoon of salt, one forth cup of ammonia and one -half cup boiling water.
Mix the lye in a pan with a quart of hot water and stir until the lye is dissolved. Let it cool, and add the lukewarm, dissolved grease. Mix the borax with a half cup of boiling water, and add it along with the other ingredients. when all the ingredients are dissolved and well mixed, pour the solution into flat, shallow pans to harden the soap. When hard, the soap can be cut into bars for use.

Martin Pilgrim: ingenious method for testing soap.
As the melted fat was mixed with the boiling lye, a feather would be stirred briefly in the mixture. If it ate the bristles off the feather, there was too much lye in the mixture. Fat would be mixed in slowly until the solution could no longer damage the feather. At that point the liquid was ready to pour out into a container to harden into a jelly-like soap.

I may just try this when the fright wears off.