Preparing your workspace before making cold process soap is essential. It helps the process run smoothly. However, as any maker can attest, even with the best planning you can forget something.
While forgetting a color just changes the design, forgetting an oil can result in lye heavy soap that may burn your skin. It can also be lye heavy if the recipe amounts are off, the ingredients are mismeasured, the scale isn’t functioning properly, etc. This creates a hard or brittle soap. It may also be irritating or drying to the touch, or have little white pockets that look like air bubbles. Testing the soap is the best way to know for sure.
How to test soap
Wait 5 days before testing your batch. During the first 2 days, the lye is reacting with the oils and turning into soap. Most of the saponification process happens then. Allowing the soap to sit a couple extra days will ensure that process is complete and the results are accurate. Then you can do the "zap test." It involves tapping the soap lightly on your tongue. It sounds weird, but it totally works. If the bar “zaps” you, it's likely lye heavy. The feeling is hard to describe, but you'll definitely notice it. Don't do this test if the soap is seeping, as the liquid may be unsaponified lye that can burn your tongue. If the soap doesn’t zap you, it's likely safe to use. You can use pH strips to be sure though.
First, wet the soap with water and rub your hands on it to form bubbles. Insert the pH strip in the lather. Then, compare the color to the chart on the packaging. Normal pH is around 9-10. If the soap is 9-10 it will turn light green. If the soap is pH 11-14, it is lye heavy. The pH strip will turn a dark green or purple in that case.
What to do if the soap is lye heavy
Don’t throw it out just yet! If the soap is slightly lye heavy (11-12 pH), it makes great laundry soap. That's a combination of shredded soap and ingredients like baking soda and washing soda, which cleans and deodorizes dirty clothes. If the soap has a pH of 13-14, it may be a bit too harsh for delicates and will work better for dirty rags, towels, etc.
In certain cases, the soap may have pockets of lye. That's typically caused by separation. In that case, we recommend throwing the batch out to be extra safe. The lye pockets can irritate or burn the skin, or may do some odd things in the laundry. We recommend wearing gloves when handling it, and double bagging it before throwing it out. If you’re concerned about disposing of the soap in your house, contact your local hazardous waste collection department.
What to do if the soap isn’t lye heavy
If the soap is 9-10 pH, it's safe to use on the skin. You may find it's balanced even if you forgot an oil. Along with adding a luxurious feeling, the superfatting level can act as insurance. For instance, if you forgot castor oil at 2%, a superfat level of 5% will cover that loss and the soap will still be balanced.
If the bars are dry but not lye heavy, there may be something else going on. For instance, a high amount of butters in the recipe can make it firm or brittle. We recommend using them at 15% or less in the batch. Learn more in the All About Butters post. Too much sodium lactate can make the soap brittle as well. Don't use more than 1 teaspoon per pound of oils.
Temperature can also affect the feel of the soap. If it gets really hot, it can crack, volcano, or form an odd texture called “alien brains.” It can also make the bars feel brittle. To keep your batch cool, pop it in the fridge or freezer for 5-24 hours. This is recommended when using sugary additives like honey or fruit puree.
If the soap is a bit too dry for your preference, it can be used as laundry soap. You can also rebatch it with equal or double parts of a soft recipe. That will help balance the soap and make it a bit softer. Learn how to make rebatch here.