Depending on your recipe, you may be able to use a salt water solution. If you are using olive oil and castor oil, you can thicken your diluted liquid soap using a 20% salt solution ( .4 oz. table salt to 2 ounces boiling distilled water). Dissolve your salt in the boiling water and using a dropper, use a little solution at a time until you get the desired thickness.
If you are using a lot of coconut oil, you may need Crothix Liquid to thicken the diluted soap.
(This is from the Soapqueen TV "Making Liquid Soap" Youtube video.)
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