Wednesday, February 9, 2011
Learning to formulate: The oil phase
The oil phase consists of oil soluble ingredients that can be safely heated and held at 70˚C for 20 minutes. This is where you'll find our emollients, emulsifiers, thickeners, and anything that is oil soluble and can tolerate heat. (Click here for a list of our emollients.)
The oil phase is generally where most of the skin feel of our products comes from as the oils, butters, emulsifiers, and thickeners you choose will determine the thickness of the product as well as the greasiness level of the lotion.
One of the main questions to ask about the oil phase is how much emulsifier to use. The general rule of thumb for Polawax is to use 25% or 1/4 of the oil phase (click here for more). I tend to use a little less BTMS-50 than I would Polawax because it really thickens up lotions well (maybe 20% of the oil phase, but it depends on how I feel that day). Each emulsifier has different formulating suggestions, so if you're using e-wax, you might want to ask your supplier for their suggestions. (I know Voyageur Soap & Candle suggests using 1% more e-wax than you would with Polawax for stability.) And if you're making your own emulsifier with the HLB system, that's a whole other post (and one I'll be going into more in the future...)
When determining the oil phase, you have to take into consideration all oil soluble ingredients in both the heated oil phase and the cool down phase. When I say everything, I do mean everything. If you're adding something like 2% IPM or 2% cetyl alcohol, include when you're determining the oil phase. Don't forget your silicones - they should be included in the oil phase. Everything that needs emulsifying into the water counts as the oil phase.
Want to know more about emulsification? Here's a post on the topic!
If we take a recipe like this one, here's what I would consider to be part of the oil phase. (Highlighted in green.)
BODY BUTTER FOR OILY SKIN WITH ESTERS
30% aloe vera liquid or water
15.5% hydrosol of choice (chamomile or lavender are very nice!)
2% sodium lactate or sodium PCA or honeyquat
2% hydrolyzed proteins of choice (I like oat protein)
22% oils - 10% soy bean oil, 12% ethylhexyl palmitate
5% shea butter (or butter of choice)
8.5% emulsifier (e-wax, Polawax, or BTMS)
3% cetyl alcohol or cetyl esters
COOL DOWN PHASE
0.5% extract of choice (chamomile)
0.5% extract of choice (wheat grass)
0.5% preservative (liquid Germall Plus)
1% Vitamin E
1% fragrance or essential oil (I'm using Clementine Cupcake from Brambleberry!)
Our oil phase consists of the oils, butter, fatty alcohol or fatty acid (like cetyl alcohol or stearic acid), esters, and silicones. It totals 34%, which means I want to use 8.5% Polawax. You might want to consider adding the Vitamin E and fragrance/essential oil into that phase, but I've found that it doesn't make a difference to the stability.
If you want to substitute oils for other oils or butters for other butters or oils for esters and silicones (or any variation thereon), go ahead. If you're using an emulsification system like Polawax, e-wax, or BTMS-50, the oils are interchangeable (but if you're using the HLB system, you know you have to re-calculate!). If you want to increase your oil phase, remember to increase the amount of your emulsifier and to reduce the amount of the water phase. If you add 4% more oils, add 1% more emulsifier, and remove 5% total from the water amount. If you add 8% more oils, add 2% emulsifier, and remove 10% total from the water amount. And so on.
Finally, for your product to behave as an oil-in-water lotion (meaning there's more water than oil), you'll want to keep the oil phase at 49% or below. We need different emulsifiers for water-in-oil lotions (meaning there's more oil than water, like cold creams), and that's a different creature all together!
Join me tomorrow for the cool down phase!