Sodium Carbonate in liquid soap

Hello everyone, 

I am getting a reaction/result that I have extreme difficulty finding information about online. I only read that perhaps superfatting may be the cause.

I was trying to make a simple spot cleaning liquid soap and wanted to add the cleansing power of sodium carbonate to my liquid soap.

Please bear with me I am not a chemist but I am really curious and love to learn!

First I made this:

100% coconut oil liquid soap with potassium hydroxide with a superfat of 5%.

I diluted it to 1 part soap paste, 3 parts water.

I made a solution of sodium carbonate with water to maximum solubility.

When I combined 1 part diluted soap with one part sodium carbonate solution, it started thickening and becoming gel-like. Within 3 minutes, it turned into an opaque paste. When I spread the paste on a surface, there are still tiny bits that are more gelled.

I tried the same process using a castile soap from creatingcosmetics, also 100% coconut oil without superfat. I got the same reaction with this store bought diluted potassium cocoate 40%.

My questions are:

1. What is the thick white paste that results from this combination? Is it some form of soap? What is being transformed into what?

2. I really want to know if liquid soap and sodium carbonate are ever mixed together intentionally for any application? Any uses or precedents?

3. I actually find the resulting thick paste interesting and it can be cosmetically elegant. When mixed thoroughly it becomes a fluffy light cream paste that blends well with exfoliants to make a scrub and holds additional oils well. Should I stay away from using sodium carbonate in a body scrub?

Thank you in advance, any help would be so greatly appreciated!



  • Carbonate has no use in soaps, it is often added for 2 purposes:

    1 To make increase the formulation pH. Soap is already too alkaline, so you don't need it.
    2 To work as an abrasive to help with cleaning.
    Only undissolved carbonate crystals will work as an abrasive. Sodium carbonate is very soluble, even more than bicarbonate, so you'd need a quite lot of it for abrasiveness, likely destabilizing the formula.
    Stick to nonsoluble fine grinded abrasives, if needed.
  • Potassium is two above sodium in the EC table. Possibly a replacement reaction producing insoluble sodium cocoate.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • sylnycsylnyc Member
    Thank you very much Gunther and Belassi for your answers. 

    I do not want it to be abrasive Gunther, I was trying to make it more cleansing/degreasing. I wanted to create a product to clean makeup sponges, it cannot be abrasive otherwise it can ruin the sponges. If it was a dishwashing product then yes the abrasiveness of the crystals would have been welcome!

    In any case, thank you for the information and your time.
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