How much essential oil do I use?
Is there a set guide line as to how many ounces of essential oil to use per ounces of other ingredients? How do you know if you have to much or not enough?
There is a general rule to use from 3% - 5% by weight of the base oil of essential or fragrance oil.
Example: If your recipe is 1000 grams of base oils, then you could add from 30 - 50 grams of scent.
That being said...every essential oil is different and has varying strengths. I would not suggest using that much anise, clove, cinnamon, etc. in a recipe since they are incredibly strong scents and can be overpowering to the senses. Some scents like clove and cinnamon can cause sensitivity to the skin as well.
Scenting soap is an art form all on its own and I always suggest starting small. Begin by mixing up scent blends and then using small amounts in your soap to begin with. You can always use a bar of soap that has too little scent but a bar that has way too much scent in it probably will not be used.
Take notes about the amounts used and the results. That way you can keep working towards improving the scent combinations and the amounts needed.