Put a few sheets of an old newspaper on your working area and a pair of gloves to protect your hands. When you're done, pour the water into a canning jar. Then, slowly pour the sodium hydroxide into the water, stirring the mixture vigorously. The solution will become clear eventually, so you might let it sit for a while.
Next, add all of the oils to another jar and heat it in the microwave for a minute. The temperature of the oils should be about 120° . The sodium hydroxide solution should have chilled down to about 120° by this time. Wait for both to reach 100° to avoid the soap to become crumbly.
Pour the oils into a bowl. Slowly stir the sodium hydroxide mixture in the bowl. Stir until the soap mixture lightens in colour and becomes thick.
This it the moment to add some herbs or essential oils if you want. Stir intensively until combined. Pour the mixture into moulds and cover it with plastic wrap. Wrap an old towel around the moulds to start the saponification process.
On the next day, check if the soap is firm. If it’s still soft, let it sit another day. When it’s hardened enough, remove the soap bars from the moulds and put them on a piece of parchment paper. The soap needs about 4 weeks to cure completely. Turn it over from time to time to expose all the sides to air.
When the soap is completely cured, place it in an airtight container for an easy storage.