Normally, additives won't effect the oils in your recipe. The recipe stays the same. Additives are used to create "something extra" in your finished bar of soap.
All Additives: As DeeAnna mentioned, it's important to read the information on the suppler's site or do some general research to be sure you don't use too little or too much to get the desired effect.
Clays, Activated Charcoal: Use 1 teaspoon - 1 tablespoon PPO (Per Pound of Oils) Purpose: Exfoliation. Can be used at a low % to bulk up a batch of otherwise thin soap, as in the case of high % of liquid oil such as olive oil; White Kaolin Clay whitens soap; colored clays add color.
Herbs: As Shari mentioned, best to infuse herbs in oil and strain before using or they make the soap feel scratchy. Powdered herbs can be added at a rate of 1/4 teaspoon PPO for a speckled effect. Herbs like calendula petals, chamomile flowers, comfrey leaves, bay leaves are soothing and color the soap.
Kitchen Spices: Use 1 teaspoon - 1 tablespoon PPO Add to oil and/or lye water to color soap. Strain before using (optional). NOTE: Cloves and Cinnamon should be used with a very light touch because they are sensitizing to skin and "heaters" in soap, i.e., will heat the soap up quickly while bringing the batch to trace.
Vegetables: Cucumber, whole or peeled. Weigh the pulp first and deduct that amount from the water used to make the lye solution. Carrot: Wonderful for face soap and sensitive skin. Infuse in olive oil or HO sunflower oil to make a pretty yellow to gold to pale orange soap.
Seaweed: Good for skin. Can be added to the oils and/or lye water and strained (optional). Also used to color soap. Somewhat stinky at first, but it fades. Find a compatible FO or EO blend to neutralize the odor. Kelp powder, spirulina, nori.
Tussah Silk: Add a small marble-size ball to lye solution. All to hydrate 5 minutes. Stir to dissolve thoroughly. Add lye to oils while pouring through a strainer to get any bits out.
That's all I can think of off the top of my head. HTH (Hope This Helps!)
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