Every once in a great while, a visitor to my event booth will ask if my soaps are made with lye. And when I answer yes, they scoff and walk away. It's hard not laugh, despite the knowledge that not everyone understands the science involved in soap making. The confusion comes from the two very different processes involved when making cold process vs glycerin (melt and pour) soaps. So let's clear things up.
Cold Process Soap
All of Thumbprint Soap's bars are made using the cold process method. Cold process basically means "from scratch." You melt some oils and butters together, add a lye solution and mix until emulsified (meaning the oil and water are no longer separating). At this point, the mixture is poured into a mold (the colors and textures happen here), where the chemical reaction will continue for the next 12-24 hours when it will be firm enough to cut. Obviously this is a super simplified explanation and a lot of testing went into my soap recipe, but you get the gist.
Glycerin (Melt and Pour) Soap
This type of soap comes as a base that has already been made from scratch (with lye) at a factory. The base comes in a loaf which is cut up and melted down by the buyer, who then adds color and fragrance and pours it back into another mold. No lye is handled by and no chemical reaction takes place for the buyer, because that part of the process was completed at the factory.
This type of soap is going to look and feel different than cold process soaps because nearly 50% of the base is made up of alcohol and sugar water. These ingredients are necessary to ensure the soap will melt when heated. Cold process soap doesn't melt. It may sweat a little on a humid day, but it won't melt.
How to Tell the Difference Between Cold Process and Melt Pour Soaps
Most of the time it's easy to tell if a soap is made from a glycerin base just by looking at it - many of them are transparent so light will pass through them. But some of the bases are made opaque by adding titanium dioxide or other ingredients, so it's not as easy to tell. In this case, you just have to read the ingredient list on the back.
Cold Process Soap Ingredients
Here is the ingredient list from my cold process Eucalyptus Spearmint Soap:
Olive oil, Water, Coconut Oil, Sodium Hydroxide (lye), Cocoa Butter, Mango Butter, Aloe Vera, Rice Bran Oil, Castor Oil, Sunflower Oil, Fragrance, Mica
Notice how the bar is opaque with swirled colors and a textured top? These things are hard to achieve with melt and pour soap bases.
Melt and Pour Soap Ingredients1) Here is the ingredient list from one of the more "natural" goat milk melt and pour soap bases (I've underlined the ingredients that are unusual in from-scratch soaps):
Coconut Oil, Palm Oil, Safflower Oil, Glycerin, Goat’s Milk, Water, Sodium Hydroxide (Lye), Sorbitol, Propylene Glycol, Sorbitan Oleate, Oat Protein, Titanium Dioxide
The soaps pictured here are definitely made with a melt and pour base. It's nearly impossible to have a cold process bar come out of individual cavity molds that smooth (you can't make these shapes with a loaf mold). And the one that looks a Jolly Rancher is too clear to be cold process soap.2) And here is the ingredient list from one of the less "natural" melt and pour soap bases:
Water, Propylene Glycol, Sodium Stearate, Glycerin, Sucrose, Sodium Laureth Sulfate, Sorbitol, Sodium Myristate, Sodium Laurate, Sodium Lauryl Sulfate, Fine Oatmeal Powder, Silica, Salt, Stearic Acid, Titanium Dioxide, Myristic Acid, Shea Butter, Lauric Acid, Tetrasodium Etidronate, Pentasodium Pentetate
This last ingredient list is a product I wouldn't buy, no matter how attractive the soap looks. A few of these ingredients I don't recognize, and it has two surfactant ingredients (sodium laureth sulfate and sodium lauryl sulfate), which shouldn't be necessary in bar soap. In fact, after reviewing the list again, I see this is not a soap at all, it's a synthetic detergent bar. So buyer beware...just because someone is selling "handmade soap," it might not actually be soap.
While I have dabbled with a few melt and pour soaps in the past (using the more natural base), I haven't made them in a long while. I know there are people out there who will argue for melt and pour, because you can make some incredibly creative soaps with these bases and you don't have to deal with the potential dangers of lye.
Since you don't get to choose the ingredients that go into melt and pour soap, I'm going to stick with cold process.
Modern Lye Soaps Don't Burn
Sure, lye is a chemical that requires precautions, but it's worth the trouble because lye soaps are amazing. This isn't your grandma's wood ash lye soap that burns your skin because they couldn't measure the strength of the lye solution back then. Rest assured, I know exactly how much lye is needed to saponify my oils, and I use slightly less than I need so there is no lye remaining in the soap after the chemical reaction has taken place. None. Zero. Zip.
Any questions? Leave them in the comments!