Select mid- or low-grade olive oil in the grocery store. Although many prefer virgin olive oil for culinary needs, high-grade oil is not recommended for soap making. Look for lye in the hardware store. You can generally find this labeled as drain cleaner, but be certain it does not contain any additives. For the purpose of soap making, the lye must be 100 percent pure.

Choose a work area that is off limits to pets and children and where you will not be interrupted. Lye is extremely caustic and heats up when processed in water, so it must be handled with caution. Minimize the risks of injury by labeling all containers and informing all family members of the risk. Wear protective clothing and goggles when processing the lye.

Add the water to a heat-proof pitcher. Slowly pour the lye into the water; never pour water into lye as this may cause a quick eruption. Stir the lye and water solution constantly until all traces of the lye are dissolved. The mixture will get very hot and may release fumes. Avoid inhaling the fumes. Set the pitcher aside in a safe location to cool. Heat the olive oil in a stock pot or metal pan to 100 degrees F.

Remove the oil from heat and pour into a large bowl. Slowly add the lye and water mixture, stirring constantly. Blend all ingredients well and continue to stir until a small drop of soap mixture leaves a mark, or trace, across the top of the soap. This means it is time to add the French vanilla fragrance oil. The amount of scent you add is really up to personal preference. Start with a few drops and adjust as necessary in future batches of soap. Stir quickly, as some oils will cause the soap to thicken rapidly.

Pour the soap into the soap mold. Cover and wrap the container with an old towel. Set the soap in a cool area to cool and set. Check the soap in 24 hours. If any water or oil is present on the top of the soap, allow it to set for another 24 hours. Remove from the mold and cut into bars. Wrap with decorative plastic wrap or tissue paper and store in a cool, dry location.