I struggled with what to title this post. I will be teaching you how to make your lotions richer and thicker, but the formulation skill behind that richness & thickness boosting is so much more than that! I will go as far as to say if you don’t know how to do this, you don’t know how to formulate emulsions. This skill is that important—really. This formulation decision is what will form the chassis of your lotion formulations: everything else will grow from there. What is that super important skill, you ask? Determining (or changing) the size of the oil phase. I know it doesn’t sound exciting, but I promise it is! Once you know how to do this you will have so much more control over your lotion formulations. You’ll start to know how rich or light a formulation will be from just looking at it, and you’ll know how to structure your own formulations based on how fast-absorbing or heavy you want the finished product to be. This skill is so essential to lotion formulation that you’ll wonder how you ever emulsified without it. Let’s dive in!

Pre-requisites

This post is part of my ongoing series on natural lotion formulation. These are the previous “episodes”:

  1. Easy Natural Lotion for Beginners (this post is a must-read before diving into this one!)
  2. How to gently scent lotions with natural ingredients (+2 free formulas!)
  3. How to naturally scent lotions with essential oils and natural fragrance oils
  4. How to make your lotions thicker

Fall 2022: Want to learn more about natural lotion formulation? Formula Botanica is currently offering a free formulation masterclass that will teach you about using natural actives and more! You can sign up here 🙂

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What’s the oil phase?

The oil phase is all the oily stuff in your formulation, added up. Carrier oils, butters, fatty thickeners, waxes, esters, emulsifying waxes, extracts in oily bases, and more. In the base formulation for this series the oil phase is 15% medium chain triglycerides and 5% Ritamulse SCG (Emulsimulse, ECOMulse) for a total of 20%.

The oil phase is also the inner phase of this emulsion, as Ritamulse SCG is an oil-in-water emulsifier. Nothing you do in the making process will change the type of emulsion you create; that is determined by the emulsifier.

Learn more: Stop Believing These 6 Lotion Myths

The amount of emulsifier you’ll need is based on how much oil is in your formulation. An easy rule of thumb is you’ll need 1% of Ritamulse SCG for every 4–5% oil in your formulation. These ingredients will mostly be in your heated oil phase (liquid oils, butters, fatty thickeners, esters, and waxes), but some could be in your cool down phase (like a heat-sensitive extract with an oil base). If you alter your formulation to include more oil, you’ll need to increase the amount of emulsifier proportionately in order to create a stable emulsion. If you reduce the amount of oil, you should also reduce the emulsifier accordingly.

I do not include essential oils or fragrance oils in the oil phase as they’re oil soluble, but not fatty, so they don’t contribute towards the richness of the formulation. They do need to be emulsified into the formulation, but I calculate my emulsifier with a bit of wiggle room so there’s plenty of emulsifying ability left over for the tiny amounts of essential oils and natural fragrance oils we use in our emulsions.

This version used Glyceryl Stearate (and) PEG-100 Stearate (a non-thickening emulsifying wax) in a direct swap with Polawax (a thickening emulsifying wax). It was very thin and not stable; you can see that it is not uniform in the sample on the black board.

Thickening emulsifying waxes vs. non-thickening emulsifying waxes

This formulation uses Ritamulse SCG (INCI: Glyceryl Stearate (and) Cetearyl Alcohol (and) Sodium Stearoyl Lactylate), which is a self-thickening emulsifying wax: it contains ingredients that emulsify and thicken our emulsions. Other self-thickening emulsifying waxes include Olivem 1000Emulsifying Wax NFPolyAquol-2W, Montanov 68 MB, and Polawax. These emulsifiers are pretty fool proof because the viscosity they add to the emulsions they create stabilize those emulsions, and are generally recommended for use at 20–25% of the oil phase.

That built in viscosity means there’s a guaranteed minimum viscosity for emulsions made with these emulsifiers. This can get in the way if you want to make something very thin (making it impossible to get really low viscosity emulsions with larger oil phases) or with a very large oil phase size (the thickener in the required emulsifier can be too much and make the formulation feel waxy). The amount of emulsifier you use will also impact the viscosity of your emulsion; using it at the higher end of the recommended range will make a thicker emulsion than one made with a lower amount.

Some emulsifiers don’t thicken our emulsions; examples include Glyceryl Stearate (and) PEG-100 Stearate and Montanov™ 202. Non-thickening emulsifiers separate thickening and emulsifying, allowing you to control the viscosity independently of creating an emulsion, and mostly independently of the size of the oil phase as well. This flexibility is fantastic, but can be a bit intimidating for new makers.

Learn more: Super Simple Moisturizing Lotion with Glyceryl Stearate (and) PEG-100 Stearate

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How does the size of the oil phase impact our formulations?

The size of the oil phase is the first decision I make when formulating an emulsion; all other decisions are built on top of that decision. It’s that important!

The larger the oil phase is, the richer and thicker the finished emulsion will be. The smaller the oil phase is, the thinner and lighter the finished emulsion will be. Decide how rich you want your formulation to be, let that guide the size of your oil phase, and build your entire formulation on top of that chassis.

  • <10% oil phase: ultralight
  • 10–15% oil phase: lightweight
  • 15–20% oil phase: mid-weight
  • 20–30% oil phase: mid to heavyweight
  • Anything above 30%: rich

While you can alter the richness and viscosity of your emulsions by including (or excluding) ingredients like gums, rich butters, lightweight emollients, and fatty thickeners, those changes will not shift the viscosity or richness to the same degree that altering the phase sizes will. A lotion that contains 30% lightweight oil will be richer than one that contains just 15% oil, but uses rich butters and oils.

The smaller the oil phase, the thinner the emulsion will be. Thin emulsions can encounter stability issues, so you may need to add something like a gum (0.2% xanthan gum is often enough) or a 1–3% of a fatty thickener like cetyl alcohol to boost viscosity a bit and stabilize the emulsion.

Fall 2022: Want to learn more about natural lotion formulation? Formula Botanica is currently offering a free formulation masterclass that will teach you about using natural actives and more! You can sign up here 🙂

How do I change the oil phase size?

You’ll need to increase (or decrease) the amount of oil, and then adjust the emulsifier so there’s still enough emulsifier to keep things emulsified.

When you first make a formulation, you’ll almost certainly be using more emulsifying wax than you strictly need. This is ok. I like to calculate my emulsifier a bit generously so I know it’ll work the first time, and to give a bit of wiggle room for anyone following my formulations. If you’re polishing up a formulation for manufacture and sale, it’s a good idea to try to use just enough emulsifier to emulsify the oil since your emulsifier will likely be more expensive than fatty thickeners, but that’s not where we are today.

Following the “1% of thickening emulsifying wax for every 4–5% oil” rule of thumb, here are some examples:

  • 15% oil, 3–4% Ritamulse SCG
  • 20% oil, 4–5% Ritamulse SCG
  • 25% oil, 5–6.25% Ritamulse SCG
  • 30%, 6–7.5% Ritamulse SCG

Another way I’ll calculate this is by adding up all the ingredients in the oil phase, and then calculating the percentage of the oil phase that is emulsifier. For our original formulation that would be 5 ÷ (15+5) = 25%. I usually aim to have the emulsifier at 20–25% of the oil phase. I generally err towards the higher end of the range with smaller oil phases, and shift towards the lower end of the range as the oil phase gets larger, but it really depends on what I’m formulating and the results I want.

It’s not best practice to use your thickening emulsifier to thicken your formulations, but there’s no denying that they will (Ritamulse SCG contains 80–90% fatty thickeners!). Using the higher end of the recommended amount of emulsifier will result in a thicker finished product than using the lower end of the recommended range. If you can get the viscosity you want by using your emulsifier at the higher end of the recommended range and that means you don’t have to go out and buy a fatty thickener, give it a try. It’s a more expensive approach, but not to such a degree that it really matters for personal use.

I chose 5% Ritamulse SCG for 15% liquid oil simply because the 5/15 number pairing was nice and round for a beginner formulation, and if a new maker’s scale wasn’t totally accurate it would still work (you could increase the oil content of this formulation to at least 20% without changing the amount of emulsifier and it would still emulsify). This higher level of thickening emulsifier also gives the formulation enough viscosity that it’s fairly foolproof—it can’t be so thin that it’ll split. Last year’s Super Simple Natural Lotion uses 15% oil and 4.5% Ritamulse SCG and that definitely works. I’ve tried as low as 2% Ritamulse SCG for 15% liquid oil, and that works, too (though it’s more finicky it’s also much more fluid—so cool)!

You should play 😄

You’ll learn a lot by making multiple versions of your formulations with less and less emulsifier to find out the smallest percentage of emulsifier you can use and the highest percentage of oil the emulsifier will emulsify. Suppliers and manufacturers often provide ranges, recommendations, and sample formulations we can learn from, but those are best viewed as starting points. For instance: I’ve read that Ritamulse SCG can emulsify no more than 25% oils, so for years I never went above that. I finally tried 30% while working on this series and it worked beautifully (I’ve got a 35% batch in testing, too—so far, so good)! It’s also worth remembering that it’s in the manufacturers’ best interest to encourage more generous usage of their products 😉

As you reduce the amount of emulsifier, your emulsions will get thinner. If you want to keep the viscosity the same, simply replace the reduced emulsifier with a fatty thickener like cetyl alcohol.

Learn more: How to make your lotions thicker

Fall 2022: Want to learn more about natural lotion formulation? Formula Botanica is currently offering a free formulation masterclass that will teach you about using natural actives and more! You can sign up here 🙂

Sample formulations

Here are three sample formulations so you can see the oil phase increase in action. Each of these formulations adds 5% oil to the one before it, and I’ve kept the emulsifier ratio constant.

Because these formulations use quite a lot of emulsifier—and that emulsifier contains thickeners—the viscosity differences are quite pronounced. If you use less emulsifier you won’t experience as large of a change.

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20% oil phase with emulsifier at 25% of the oil phase

Heated water phase
67.25g | 67.25% distilled water
5g | 5% sodium lactate (USA / Canada)

Heated oil phase
6.75g | 6.75% Ritamulse SCG (USA / Canada / UK / AU)
20g | 20% medium chain triglycerides (USA / Canada / UK / Aus / NZ)

Cool down phase
1g | 1% Euxyl™ k 903 (USA / EU)

For full instructions, please read this post.

25% oil phase with emulsifier at 25% of the oil phase

Heated water phase
60.5g | 60.5% distilled water
5g | 5% sodium lactate (USA / Canada)

Heated oil phase
8.5g | 8.5% Ritamulse SCG (USA / Canada / UK / AU)
25g | 25% medium chain triglycerides (USA / Canada / UK / Aus / NZ)

Cool down phase
1g | 1% Euxyl™ k 903 (USA / EU)

For full instructions, please read this post.

30% oil phase with emulsifier at 25% of the oil phase

Heated water phase
54g | 54% distilled water
5g | 5% sodium lactate (USA / Canada)

Heated oil phase
10g | 10% Ritamulse SCG (USA / Canada / UK / AU)
30g | 30% medium chain triglycerides (USA / Canada / UK / Aus / NZ)

Cool down phase
1g | 1% Euxyl™ k 903 (USA / EU)

For full instructions, please read this post.

 

Gifting Disclosure

The Euxyl™ k 903 was gifted by Formulator Sample Shop.
The sodium lactate was gifted by Bramble Berry.
Links to Amazon are affiliate links.