Here's what you need
3 PLASTIC BUCKETS
Step 1: Step One: Apply Fire To Wood
Now after burning that wood collect the ashes in a big 5 gal plastic bucket make sure the coal are not hot and melt through the bucket.
Fill the bucket about half way should be enough.
Step 2: Step Two: There's holes in your bucket
Step 3: Step Three: Just Add Water
Take the bucket with rocks and holes and put that in the other one. Fill it with the wood ashes.
Now just add water, this must be soft water or distilled water, the best to use is rain water.
Step 4: Step Four: Your Lye is Done
You can test the acidity with a PH meter make sure it goes from 1.0 - 14.0 14 is the PH level for making soap.
Old ways of telling if you lye was ready for soap making was it could dissolve a chicken feather, or if a egg is placed in water it would float above the water like a bobber.
Or you could boil it, DO THIS OUT DOORS!