Orthogonal Thought | Random musings from the creator of Cooking For Engineers and Lead Architect of Fanpop





Make Natural Soap At Home - FAQs

Posted 9 August, 2012 at 8:45pm by Tina Jiang
(Filed under: Soap Making)

Since I wrote the first blog post about making natural soaps at home four years ago, I've been getting a lot of questions. I noticed some recurring themes and picked out the most common questions. I tried to answer them to the best of my knowledge… hope this is helpful for everyone.

Can I substitute ingredients, e.g. use different oils or liquids?
Can I add fresh fruits, herbs, flowers, etc. to the soap?
When do I add scents (fragrance or essential oils) to the soap?
What can I use to color soaps?
Do I have to measure the temperature of the oils and the lye solution?
Why do I need to weigh the ingredients with a scale?
How long can I keep the soaps? How do I know if it's still good to use?
How do I make milk soap?

Can I substitute ingredients, e.g. use different oils or liquids?
Yes you can, but you need to recalculate the amount of lye needed (click here for an online lye calculator). This is because different oils require different amounts of lye to saponify, and changing oils without adjusting the quantity of lye can result in soaps that are either oily (excess oil vs. lye) or caustic (excess lye vs. oil) which is dangerous to use. Please make sure to always recalculate the amount of lye when substituting oils.

Depending on the oil, there may or may not be good substitutes. For example, coconut oil is very important in soap recipes because it provides fluffy lather, which few other oils do except for palm kernel oil, which can be used as a substitute for coconut oil. Note that palm kernel oil is not the same as palm oil - the former is obtained from the kernels of the fruit of the oil palm tree, and the latter from the pulp. They vary in chemical composition and therefore contribute different properties to soaps. Coconut oil is obtained from the meat of the coconut from the coconut palm tree, which is different from the oil palm tree where palm kernel oil and palm oil comes from. All three are solid at room temperature and gives hardness to soaps, but only coconut oil and palm kernel oil contributes fluffy lather. Palm oil is easier to substitute, e.g. you can use tallow, lard, or vegetable shortening. Olive oil may be substituted with canola oil, vegetable oil (aka soybean oil), or corn oil, etc.. Just make sure to recalculate the amount of lye needed for your specific recipe.

As for liquids, instead of water you can use milk (makes milk soap), or tea, etc.. See last question on the FAQ list for how to make milk soap. If you are using tea or water that's been infused with flowers, fruits, vegetables, or other plant materials - unfortunately after the liquid is mixed with lye there won't be any natural fragrance or skin benefiting properties left, and the color of the tea may change as well. So I just use water and add essential oils after the lye and oils have been combined and thoroughly mixed.

Can I add fresh fruits, herbs, flowers, etc. to the soap?
Fresh fruits, herbs, flowers, etc. will not survive the chemical reaction with lye. It's best to add dried materials to the soap mixture at the same time essential oils are added, i.e. after the lye and oils have been combined and thoroughly mixed. Take care not to add too much since these ingredients tend to spoil faster than the soap itself and will reduce the life of the bars.

When do I add scents (fragrance or essential oils) to the soap?
Add scents after the lye and oils have been combined and thoroughly mixed, i.e. when the saponification process has started and the lye and oils are reacting to make soap. Some fragrance and essential oils may cause the soap mixture to seize (cold process only, not a problem for hot process), so make sure to mix quickly then pour it into molds. Do mix well though otherwise there may be little pockets of fragrance/essential oil inside the soap (speaking from experience :).

What can I use to color soaps?
There are various ways to color soaps. Some options are:
1. Pigments - they are in powder form and can be purchased online from soap making supply websites (click here for some examples). I like to mix them with a little bit of glycerin (so it blends better) and add to the soap mixture. Glycerin can be purchased at any drugstore or Walmart.
2. Dyes - they are in liquid form and can be mixed with water. I have not personally tried it yet. They can also be purchased from soap making supply websites.
3. Ground up natural substances - for example, cocoa powder, cinnamon powder, coffee grounds, tumeric, paprika, etc.. In addition to color, some may also provide exfoliation properties (e.g. coffee grounds). Mix with glycerin and add to soap mixture.
4. Food coloring - not really a good option for soap making, since the colors aren't true due to the chemical reactions with lye and fade over time in storage. Better off with one of the other options.
5. Crayola - I've successfully used crayons as colorants, since they are pretty much pigments in a wax base. If they are safe for young children to play with, I think they are safe to use in soaps. You don't need a whole lot - for a 1 pound batch I generally use half of a stick, and for a 2-3 lb batch a whole stick. It also depends on how saturated you want the color to be. Not all crayon colors come out true in soaps, so if you need the color to be exact this is not a good option. The colors that tend to stay true (from my and others' experiences) are yellow, orange, brown, black, and white. Red tends to end up a shade of pink, so anything with red in it (e.g. burgundy, purple, etc.) will come out different. I have not tried blues and greens much but from what I read it depends - Cerulean blue and greens made with Cerulean blue (e.g. blue-greens, teals, forest green, jungle green) are good, whereas Prussian blue and colors that contain it (e.g. navy, midnight blue, purple, violet, some greens) are no good. I personally think for hobby purposes it's kind of fun to experiment and see how the colors comes out. To use the crayons, I put it in a bowl with a little bit of oil, then melt it slowly (a few seconds at a time) in the microwave until completely dissolved, then mix it in with the rest of the oils (prior to mixing with lye solution).

Do I have to measure the temperature of the oils and the lye solution?
From my experience, the best results occur when the temperatures of the the oils and lye solution are within 20 degrees Fahrenheit of each other (I generally work between 100-120F, sometimes higher but usually not below 90). If there's a huge difference in the temperatures, it's likely to interfere with the saponification process. I've had this happen where (in the winter) the oils were much cooler, and when mixed in with the hot lye solution, it cooled down the whole mixture enough that the saponification process was stalled. So now I always check the temperatures and if one is too hot (usually the lye solution), I'll wait for it to cool down, or if it's too cool (usually the oils) I'll warmed it up a bit in the microwave before mixing the two together.

Why do I need to weigh the ingredients with a scale?
In my opinion using a scale to weigh the ingredients is the only way to guarantee consistently good and safe (i.e. not caustic, not too oily, etc.) results. I would never eyeball the ingredients because I don't want to risk making a batch of failed and possibly caustic soaps. In addition, a lot of (if not most) soap recipes are written based on weight, not volume measurements, so that's another reason to use a scale.

How long can I keep the soaps? How do I know if it's still good to use?
How long homemade soaps will keep depends on how it's stored (cool, dry places are best) and the recipe itself (% of superfat/lye discount, i.e. amount of extra oil included for moisturizing effects, amount of dried plant materials added, etc.). My general rule is to use them up within six months for best results. Overtime, they may develop orange/brown spots or start to develop a stale smell if the oils are going rancid. Dried plant materials may start to rot and grow mold, especially in a hot and humid environment. If the soap looks and smells ok, even after a long period of storage, it should be fine to use.

How do I make milk soap?
You can add milk in two ways:
1. Substitute milk in place of water (all of it or just a portion)
2. Add powdered milk to the soap mixture
I don't have a ton of experience making milk soaps, but here are some helpful articles written by David Fisher on this subject:

My other soap articles:
Making natural soap at home - basic recipe:
Making soaps in the round with a marble pattern:
Making soaps in a slow cooker (the soap is usable right away):

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