Making Soap With Science!




Introduction: Making Soap With Science!

Soap: everyone has soap, but very few of us appreciate it. Haven't you ever wondered how soap is made? Neither did we, but we'll tell you anyway. In this Instructable I hope to teach you, the reader, how we make soap and all of the science behind the reactions and why it is such a good cleaner.

A quick overview of what we will be doing is firstly we will need to select our fats and oils. This is completely up to you, but in order to make a decent soap I would recommend balancing the numbers in the soap calculator. For my first soap all I used was vegetable shortening. This did not go over well because it was not very well balanced. However in my second try I used both coconut butter and olive oil making it a much better soap. After you have also chosen you desired herbs, essential oils and coloring you will need to figure out how much lye or potash you will need to fully react to the fats or triglycerides. Then after all of that preparation you can start to make the soap, by first melting all of the fat, then adding the required amount of lye/potash, waiting for the reaction to fully occur and pour it in your mold to set.

Step 1: Materials You Will Need

  1. Hot top or stove that can heat fat to 150-160°F(49-54°C)
  2. A saucepan to heat your fat in. In the lab we used a large beaker
  3. Your choice of fats, oils, herbs, essential oils and coloring
  4. A scale to measure the weight of your fat
  5. A thermometer
  6. A stirring spoon
  7. Molds to pour the soap in
  8. Lye or Potash
  9. pH test strips
  10. Protective gloves and eye-wear
  11. (In our case)Graduated cylinder

Step 2: Fats, Oils and Adjuncts

The fats and oils you use will determine the properties of the soap you make. When you put the fats into this calculator it will give you values for Hardness, Cleansing, Condition, Bubbly, Creamy, Iodine, and INS as well as a range for them to be in and what they mean for your soap. In my soap I used both olive oil and coconut butter. They will also determine how much lye or potash you will need to add to your fats and oils to make it go through the reaction known as the saponification reaction.

In the soap I am using for an example in the next steps I used 50% coconut oil and 50% olive oil. This gave me the values of 48, 34, 46, 34, 15, 48 and 182 in the same order as above. This shows that I will have a balanced soap. Most of these are within the range that the soap calculator asks for and if they are off it is marginal.

Along with adding fats and oils there are plenty of things you can add to modify your soap. These are known as adjuncts. Things like essential oils, herbs and coloring. The only thing that will really change how your soap will turn out physically is the essential oils. All they bring along with them is some extra triglycerides or fat molecules and a minor amount at that, but the amount is minor and nothing to worry about. Otherwise adding these makes your soap have a great smell, texture and/or color.

Step 3: Saponification Reaction

This is the reaction that creates the soap molecule. What this says is for every triglyceride you will need 3 molecules of lye/potash or sodium/potassium hydroxide. WARNING! Lye/Potash is very basic and detrimental to skin and is also irreversible. Wear gloves, safety goggles and close toed shoes for making soap. Triglycerides are made up of many different or similar molecules known as fatty acids. Fatty acids have many different properties to themselves. They can be saturated, without a bend in the chain, monounsaturated, with one bend in the chain, and finally polyunsaturated, with more than one bend. Depending upon this we can tell if the fat will be a oil or solid. The longer the chain is and the more bends in the chain will make it harder to melt. This effects your soap in a way that it will be softer or harder when you use it. If you use more solid fats to make the soap it will not melt as easy or be harder. If you use more oils you will find you soap softer and easier to melt. Once the reaction has taken place you will be left with both a glycerol molecule and 3 "soap" molecules. This is where the explosives in "Fight Club" come from. They come from separating the glycerin from the fatty acids and nitrolyzing it to make nitroglycerin or more commonly known as "TNT".

This also derives something else important to making soap. Through this we can find the Saponification Value(SAP Value). All the SAP Value is, is how many grams of lye or potash you will need to make the soap per gram of fat. For example say we have a quarter pound of fats and its SAP Value is 0.137 we would need to find that amount of pounds in grams. Which after a quick Google search is 113.398 g. Then multiply that by 0.137 to get the necessary amount of grams of lye to make the soap. Which is in this example 15.5 g.

Step 4: Calculate

Before we get into making the soap we need to find the amount of lye or potash we will need to completely transform our fats and oils into our soap. We do this through using the SAP Value. In the making of my soap I used lye, this doesn't matter you can use either, but I will be calculating this accommodating to lye. You will find your SAP Value using this Soap Calculator. For my 100g of fat or quarter pound I will be using the SAP Value of 0.133. So by multiplying them together I get 13.3 g of NaOH(Lye).

This could be the end of it if you need it in solid form and in that case you can move on to the next step. However for my soap I will be using 10.3 Molarity NaOH. All this means it that there is 10.3 moles of NaOH in one liter of water. Wait, what is a mole? Well a mole is the grams of a substance that has 6.02x10^23 number of molecules in it. Don't let the big number scare you. What I plan to do with it is use it to convert from grams to mL of the 10.3 Molarity solution. You just need to know that one mole of NaOH is 39.89 g. To convert the grams we have to add to make our soap, to moles we will need to divide, in my case, 13.3 by 39.89. However if you are using potash it will instead of being 39.89, it will be 56.1. Once that calculation is done, for me it was ~0.33, you will have the moles of NaOH required to make all of the soap. The next and final calculation is to convert the moles to mL. Since we know that there is 10.3 moles per liter we can simply divide the number of moles we need by the molarity and then multiply the whole thing by 1000 to get mL of solution required. Finally ending at 32 mL, you can move on to making the soap itself.

Step 5: Melting the Fat and Keeping the Right Temperature

Put your fat into the saucepan, ensuring as much fat as possible enters the pan. Try to keep the temperature of the fat in the saucepan between 120 and 130°F(49-54°C) during the entire soap making process. It's important to maintain a decent temperature. If your solution gets too hot, it will probably cook the fats, and if it becomes too cold, the saponification reaction will be slowed or not occur at all. After 5-15 minutes, your fat should be melted and in a liquid form. Once all of the fat has liquefied, proceed to the next step.

Step 6: Adding the Lye/Potash

Be very careful during this step. Lye/Potash will burn skin on contact, and can cause permanent, irreversible damage if in contact with eyes or ingested. Always wear safety goggles, closed toed shoes, and gloves when handling lye.

While stirring the liquefied fat, slowly begin to pour the lye into the pan. Ensure you have the proper amount of lye for this step, as too much lye may end up burning your skin when you first go to use the soap, and too little will make your soap unstable and crumbly. Continue to stir after all of the lye has been added, and until the solution reaches a thick, pudding-like consistency known as a trace. I would say stir for a minimal of five minutes, we want as much of the fats to react as possible. Here's a great example of a good trace. Once you've reached this state, you can progress onto the next step.

Step 7: Wait...

After the soap has reached the trace state, pour it into whatever mold you have prepared. Let this sit for at minimum a day or so. If you decide to age your soap, a practice used by soapmakers, this may take anywhere from a few days to several months, depending upon your preferences. The advantages of aging is, the process allows soap to solidify further, and should make for a better overall soap. Once you've set your soap in the mold, you can proceed to everyone's favorite step: Clean up!

Step 8: Clean Up!

When you're done with your work, it's always important to make sure you clean everything. First you should put away any materials that did not come in contact with the lye or potash. The disposable gloves can be thrown in the trash. The saucepan can be washed in a sink as long as you added the right amount of lye/potash to turn the fat into soap, however if there was a mess up, then you should swish some vinegar in to neutralize any basicity left in the pan. If the scale came in contact with lye/potash the contact area must be rinsed with vinegar. If you used dissolved lye/potash, the graduated cylinder must be rinsed with vinegar as well. Once you have put everything in its respective place and neutralized any lye/potash you can continue to wait for the soap to harden.

Step 9: Enjoy!

The soap helps to clean thanks to its polarity. Soap has two different polar ends a hydrophylic end and a lipophylic end. The hydrophylic end is formed by adding the lye or potash to the fat. Doing this creates a polar end that is attracted to water thus the name hydrophylic. The other end is non-polar because it is made up of a fatty acid and because of that it is attracted to fats. When soap is used to clean hands its lipophylic ends connect to the fats, grime, and dirt on you hands creating a micelle that looks like circle surrounding the fats. Once the micelle has formed its hydrophylic ends follow the water that it is attracted to and then goes down the sink.

The polarity characterizes the attraction to other molecules. As we know we can't mix oil with water since water is polar and oil is non-polar. What polar means is the molecule has both a positively and negatively charged side. Non-polar means that it is the same charge all around whether it be positive or negative.

It is also important to measure the pH of your soap before using it because if it is higher than 10 it will most likely burn your skin. What pH tells us is the amount of either H+ or OH- is in a substance. The H+ stands for acid and the OH- stands for basics. That is why NaOH and KOH are both near 14 on the pH level. To do this you will simply need to dissolve some of your soap in some water and test the pH with a test strip. The target area is within 8-10 pH. This is ideal because if it is too high the soap will burn your skin and if it is too low it is probably too crumbly.

The first soap we made was not put together well and thus not done to well leaving us with small amounts of soap. It works just fine, but the main thing that messed it up was that we only used shortening making the soap unbalanced. This is the importance of finding the right ratio of fats for your soap. So, for example when I did it the second time the soap was more balanced from the beginning making the soap much easier to form and more yielding. Of course comparing your or my soap to professionals/commercial products is daunting because they have had their technique down for years possibly centuries, but I can say that compared to my classmates the first soap I made was not nearly as good as the others, mostly because it was not balanced at the least and only had one fat. Where others were using something like two or more. However my second soap was spectacular because I used two fats that balanced it well and made it smell good. Either way I hope that your soap turned out well and that you have learned something about the science of soap-making.

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    6 Discussions


    1 year ago

    Just wanted to say: VERY good tut!

    Addition: You CAN also make cold process soap with room temp ingredients. Let the lye solution cool and, after gently heating the solid fats in the liquid fats until the solids are just melted, let them cool to just warm to the touch. Combine and stick blend in bursts until you achieve trace. Much easier than hot process or trying to get the lye and oils to within a 10°F temp range.
    And a correction? It's much safer to mix the lye in either a stainless steel container or a plastic one with a recycling rating of either 2 or 5. I use natural yogurt containers with a recycling rating of 2, and let the lye cool to room temp. Afterwards, all I need to do is rinse it in cool water. There's not enough lye left in it to cause any plumbing issues.
    Happy soaping!

    Nikolai Nielsen
    Nikolai Nielsen

    3 years ago

    I noticed that you said that glycerine is used in making nitroglycerine then TNT. it's actually used in dynamite which is nitroglycerine mixed with a particular type of clay to stabilize it. TNT stands for trinitrotoluene


    4 years ago

    I love the idea of olive oil in soap! It's so good for your skin!


    Reply 4 years ago

    Thank you for the comment. I also see that you have looked at the other Instructables that my peers made and made a comment there. I looked at some of yours and was wondering what your technique is for taking those pictures? They look really good.


    Reply 4 years ago

    I have enjoyed seeing all of the soap projects come through! My advice to get good photos is to use good natural light. I don't have an expensive or high-tech camera. Just a point-and-shoot along with great lighting! How do you like using homemade soap compared to store bought?


    Reply 4 years ago

    Idk. It's definitely more fun and enjoyable because you put the time and effort into making it, and its personalized to your wants. You planning to make some yourself? If so let me know how it comes out.