Today we’re looking at stearic acid, and how it behaves when melted together with olive oil at different ratios. Stearic acid is a pretty humble ingredient—mine is unassuming white beads that are bigger than cetyl alcohol, but not by much. We use it to thicken and harden our products when we want thickening and hardening, but we don’t want waxiness. Because stearic acid is an isolated fatty acid it thickens without adding the tack or brittle stiffness that wax can contribute, meaning waxes are typically not a good substitution for stearic acid as they’ll bring a few things to the party that weren’t invited.
Stearic acid is a naturally saturated occurring fatty acid that’s found in many oils we love. You’ll find it in relatively high percentages in hard oils and butters like cocoa butter (24–37% stearic acid), shea butter (20–50% stearic acid), and tallow (14% stearic acid)—it’s a big part of what makes them hard oils!
Stearic acid melts at 69.3°C (156.7°F) (that’s a higher melting point than beeswax!), making it a very effective hardening ingredient that raises the melting points of our products without adding any waxiness. It can be sourced from animal or plant sources, or synthesized, so if the origins of your ingredients are important to you, be sure to ask your supplier. You’ll also find derivatives of stearic acid in many other ingredients, like magnesium stearate and stearyl alcohol, and find it on ingredient lists for many different products—everything from soap to lotion to cosmetics. It creates a hard bar of soap with stable, creamy lather, contributes to stable emulsions, thickens and hardens concoctions, and adds occlusiveness. It’s pretty darn useful! It’s also very shelf stable and inexpensive; I purchased a pound of the stuff for less than $5 at Windy Point!
This experiment is a sort of counter-point/companion to my A Quick Guide to Cetyl Alcohol & Liquid Oil Ratios. This experiment uses the same methodology, allowing easing comparing and contrasting of the two so we can start to understand how these two simple ingredients differ from one another and contribute to our final products.
As with the cetyl alcohol experiment, this one uses ratios: 3:1 through 1:6, with the first number being the stearic acid and the second being liquid olive oil. I used a single gram as my unit, so 3:1 is 3 grams stearic acid, 1 gram olive oil. Each mixture was melted together, swirled to combine, and left to cool for about 16 hours at room temperature before inspection.
Something I noticed quite promptly is that the results of this experiment would’ve been very different if the mixtures had been stirred while they cooled instead of being allowed to cool while standing still; be sure to contrast the results of the all-together-and-stirred mixture at the end to see what I mean! I intentionally didn’t stir to keep the methodology consistent with the cetyl alcohol experiment, but going forward I’d definitely recommend stirring anhydrous stearic acid concoctions as they cool if the stearic acid concentration is 20% or higher.
Alright, without further rambling, let’s dive in!
3:1 (75% stearic acid)
Has a very crystalline appearance with what appears to be an oily sheen on the surface. When I poke at it, it’ll slide up from the bowl and come up in a single disc. It breaks easily and feels fairly soft, but when rubbed into the skin it becomes very obvious that there are two parts of this disc—the softer, semi-firm bits and some flat, shard-like glassy fragments that didn’t stay in solution. These do not soften when they sit on the skin and don’t rub it at all, but they aren’t sharp or uncomfortable (unlike allantoin shards!); I just look like I’m wearing some strange large-flake glitter.
2:1 (66.6% stearic acid)
Very similar to 3:1, with the same crystalline appearance. When I push at the mixture it slides up as a single wafer that is easily broken it half. It’s not stiff enough to snap, it mostly just bends until it sort of tears apart. The glossy shards are smaller than before, giving an effect that’s sort of glittery on the skin with no sensation of itching or pricking—just shimmering. They still don’t melt or rub into the skin.
1:1 (50% stearic acid)
This one looks less crystalline, with spots of what looks like frost instead of the entire disc being crystal-esque. When I try to slide it up in the bowl it splits down the center. When massaged between the fingers it has good slip, but feels a bit powdery—almost like white wheat flour.
1:2 (33.3% stearic acid)
Just a few “frost” patches. Quite soft—easily squashed with a finger. Rubbing my finger on the top brings up a bit of light oil. I can easily pick up some of the creamy mixture just by pressing my finger into it. It has quite good slip, but still has that powdery feeling; not powder-dry, though, powdery-not-entirely-smooth. It’s odd. The shimmer/glitter/shard effect is still there, leaving me looking like I’ve got some neat large-flake glitter on. (See the stirred-while-cooling variation on approximately this ratio/percentage at the end to compare—super cool!)
1:3 (25% stearic acid)
Slightly crystalline in appearance, but no “frost” patches. Soft and squishy to the touch, with that powdery/almost mealy consistency. When massaged into the skin it feels like olive oil with some added glittery bits.
1:4 (20% stearic acid)
Soft and shimmery, oozes a bit of oil when poked. Glides across the skin well, with almost no noticeable shimmery bits. The dry/dusty/slightly mealy sensation is gone—it pretty much just feels like viscous olive oil.
1:5 (16.6% stearic acid)
Soft, with a slight oily sheen on top. When I press through it with a finger it has a really interesting slush-like texture; like an oil slurpee! It’s very neat. It melts quickly and massages into the skin beautifully, with no shimmery glitter bits. It feels just like a slightly thicker olive oil.
1:6 (14.3% stearic acid)
This one had three noticeable consistencies at first—a hard top, a creamy center, and some liquid olive oil at the bottom. Once I smooshed it together a bit with a finger (it’s very soft) the consistency was like a blend of a frozen drink and an oil gel—very cool! Great slip, lovely mild viscosity, and absorption on par with plain olive oil.
11:23 (32.4% stearic acid)
I did this one a bit differently; after examining 3:1 through 1:6 I put all the experiments in a single bowl, melted them together, and then stirred the mixture consistently as it cooled to get a bit of an idea of how the consistency changes when it is stirred while cooling instead of being allowed to sit still. This one was really different, with a consistency like thick, creamy mashed potatoes. It was soft, and melted readily into the skin without liquefying on contact. There were no shimmery bits, either, and I noticed a lovely occlusive feel that is much lighter than the occlusiveness of beeswax. Stirring while cooling is definitely the way to go if you’re using stearic acid in high percentages.
- Stearic acid behaves very differently if stirred when cooling vs. not
- It gives a mild occlusive feel that’s quite lovely
- In higher percentages it can feel a touch mealy or powdery
- The slip is good, but nowhere near as luxurious as cetyl alcohol
- Compared to cetyl alcohol it doesn’t create a dry, silky feel
|3:1||Not really||Yes||Some of it vanishes quickly, but the crystalline shards never melt.||No||Ok|
|2:1||Not really||Yes||Some of it vanishes quickly, but the crystalline shards never melt.||No||Ok|
|1:1||Not really||Yes, soft||Some of it vanishes quickly, but the crystalline shards never melt. There are fewer shards, though.||No||Good, dusty/powdery feel|
|1:2||No||Yes, soft||Some of it vanishes quickly, but the crystalline shards never melt. There are fewer shards.||No||Good, dusty/dry feel|
|1:3||No||Yes, very soft||It feels like olive oil on the skin with some added crystalline glitter bits that never melt. Fewer shards, but they are still there.||No||Good, dusty/dry feel|
|1:4||No||Yes, very soft||It feels like olive oil on the skin with some added crystalline glitter bits that never melt. Very few shards, but they are still there.||No||Good|
|1:5||No||Very soft||Almost instant, no shards.||No||Great|
|1:6||No||Like a frozen drink||Almost instant, no shards.||No||Great|