Add the olive oil and coconut oil to a large, (6 quart minimum) crock pot. Turn the crock-pot on high.
While the oils are warming, put on your safety gloves and goggles, and carefully measure the potassium hydroxide lye into a stainless steel or pyrex bowl.
Measure the water into a medium stainless bowl or pyrex pitcher. Set the container with the water into your sink, then very carefully tip the lye flakes into the water. Stir to dissolve.
When the oils in the crockpot are warm, carefully tip the lye solution into the oils. Leave the crockpot on high.
Use an immersion blender to blend the oils and lye solution together. Immediately after adding the lye solution to the oils, blend for about 5 minutes, until the mixture looks uniformly opaque and begins to slightly thicken. For the next 30 minutes, come back and blend the soap paste about every 5 minutes. The mixture will get thicker and thicker, progressing through an icing texture to something like Elmer’s glue.
Cook Soap Paste
When the soap mixture becomes too thick to blend with an immersion blender, lid the crock pot and cook the soap mixture for 3 hours on high.
Every 30 minutes or so, come back and fold and stir the soap paste with a heat-resistant silicone spatula or heavy wood spoon to ensure the soap paste cooks evenly.
As the soap cooks, it will become increasingly translucent, moving from a runny white liquid to a puffy taffy texture to, eventually, a yellowy-clear, thick, translucent gel.
Test Soap Clarity
After 3 hours, or once the paste looks fully translucent and gelled throughout, check the soap with a clarity test.
Measure out an ounce of soap paste (about a golf-ball sized blob will do it). Add 4 oz (1/2 cup) of boiling or very hot water to the soap paste. Stir gently until the soap paste is totally dissolved.
Allow the dilute soap to cool. If the soap is opaque, or if a scum of oils floats to the surface, continue cooking your soap paste for another hour before re-testing.
If the dilute soap is clear (it needn’t be colorless, just translucent), proceed with dilution.
Dilute the Soap Paste
Add 10 cups water to the soap paste in the crockpot. Break up the soap paste into the water as best you can but don’t worry about the paste dissolving fully.
Lid the crock pot and turn the heat to warm for 8 hours or overnight. If you happen to walk by, give the soap a stir to help it along but don’t worry if you can’t.
After 8 hours, if you notice chunks of remaining soap or thick skin of soap forming even after the chunks of soap dissolve, add another cup or two of water to further dilute the paste.
When your soap is fully dissolved with no chunks of soap paste remaining, ladle your dilute soap into a perfectly clean and dry 1-gallon glass or plastic jug.