Monday, January 18, 2010

NaOH Biodiesel Glycerin (BDG) (Hybrid) Gel Soap

Believe it or not you can use your NaOH (sodium) based BDG to make a liquid or gel soap. This is possible because the NaOH BDG has saponifiable ingredients left in it. These saponifiable elements will be turned into KOH soaps. The soap will be a really nice gel soap at a 50:50 soap to water dilution. The soap will be a thickened liquid or gel because the sodium soaps will act as the thickener in the soap. There will be no need for any thickeners such as borax.

The trick to this working just right is full saponification of the saponifiable elements left in the NaOH BDG. If you do not fully saponify the BDG you can end up with a thin liquid that will congeal into a mass. No amount of dilution will give you a nice liquid or gel.

To be sure you have fully saponified your BDG you should do a SAP test on your BDG. This way you know exactly how much KOH it will take to fully saponify your NaOH glyceirn.

This recipe is a very basic recipe. Once you have mastered this recipe you can go on to adding any other ingredients to add properties to your gel.

You will need the following;
  • 32oz NaOH BDG
  • KOH SAP value for your NaOH glycerin
  • 1.6oz KOH (26% SAP used)
  • 32oz Distilled water
  • pH Paper

Melt your NaOH BDG.

Mix your KOH caustic water.

Add the caustic water to your melted BDG and mix with a stick blender for about 5 minutes. Notice that the BDG will go from a dark brown color to a tan color. This indicates that the saponifiable elements in the BDG are starting to be saponified.

Heat the soap to 180*F and hold it there until the soap neutral and has a pH around 10.5. This could take up to 3 hours. Check the pH of the soap every 30 minutes or so. You should notice the soap go from the light tan color back to a translucent brown color.

Allow the soap to cool.

The soap should be very thick and transparent. The pH should be between 10 and 10.5. If the soap is still thin or the pH is less than 10 you will need to add more caustic (KOH) water. Mix 1/2 ounce of KOH with 3 ounce of distilled water. Add this 1 Tablespoon at a time until the soap thickens and the pH is between 10 and 10.5

To learn more about soap making from Biodiesel glycerin, be sure to check out our great book "Making Biodiesel Glycerin Soaps". It contains lots of great tips & tricks for getting the best soap out of your Biodiesel glycerin. Click here to learn more.

Happy Soaping :)

Copyright Knice-N-Clean Soap Company LLC 2010 All rights reserved


  1. Thank you Topcat :)

    I've been doing a lot of playing with using sodium soaps to thicken potassium soaps.

    BDG is a unique ingredient that allows you inexpensively do some cool experimenting.