Lye(sodium hydroxide) and water (often distilled) are essential to the soap making process.
When sodium hydroxide beads or flakes are mixed with distilled water it creates what we call a lye solution.
This solution is then mixed with oils causing a chemical reaction called saponification.
I won't bore you trying to explain the actual science behind these chemical reactions since that level of chemistry is above my understanding. I start to fall asleep just reading about it.
My personal opinion is that you don't need a science degree to make wonderful soaps (though if you have one, I'm in awe!).
You do need to understand the importance of mixing the correct ingredients and measuring the correct quantities. The result is beautiful handmade soap.
Calculating the amount of sodium hydroxide required for a soap formula can be a nuisance. That's why on-line calculators are such a blessing.
There are many free ones available but my favorite is at a website called SoapCalc.
It provides a wealth of information and allows you to really play with your homemade soap recipes.
I've mentioned that distilled water is essential to making soap. This is true, however, many liquids contain water and can be used as well.
Milks are one option.....cows milk, coconut milk, goats milk, buttermilk, almond milk, rice milk and ewes milk.
Vegetable and fruit juices, aloe vera juice, coffee, regular tea, herbal teas, wine and beer are also possible alternatives.