In this post, Humectants: Propylene glycol & dipropylene glycol, Tyler asks: What is the HLB value of butylene glycol?
Butylene glycol doesn't have an HLB value because it isn't oil soluble. HLB values are assigned to emulsifiers and oil soluble ingredients. Since butylene glycol is water soluble and doesn't need an emulsifier to mix with water, it doesn't have an HLB value.
Related posts on the HLB system:
GLYCERIN IS WATER SOLUBLE
I'm not sure where the idea that glycerin is oil soluble arose, but it really isn't. In fact, glycerin is completely water soluble, meaning it mixes completely with water.
In the area of solubility, "like dissolves like" means that something polar will dissolve something polar. Water is polar and glycerin is polar, so we should expect that glycerin will dissolve in water. If something dissolves in water, we call it water soluble. As its solublity is really high in water - it's called "completely soluble" so add as much as you want - we can call this water soluble.
ARE ESSENTIAL OILS CONSIDERED WATER SOLUBLE?
In this post, Why did I buy that again? Cera bellina - an anhydrous eye gel, Matilida asks: I'm wondering, do you think a couple drops of Lavender Essential Oil would work in this formula? I'm not sure if an EO counts as water based. I love the texture, but am walking around thinking I smell oil on my face, so thought the lavender EO may be gentle enough to use for the smell.
You could add an essential oil to any anhydrous or non-water containing product or any emulsified product easily by adding it at the suggested usage level. (As always, check to see if you can use that essential oil in that capacity and at the level you wish.) Essential oils are oil soluble, so you can add it to those products as it will mix well.
Having said all of this, because the original recipe for the eye gel is anhydrous, you could mix a few drops of lavender essential oil into it if you wish. I don't like fragrances on my face, but you might, and that's really the decision you have to make.
And please don't measure essential oils in drops. It's way too easy to go over the recommended usage rate - how many drops makes up 0.5%? 1%? - and it's hard to replicate that in your recipe if you increase or decrease it!
Related posts on essential oils:
Essential oils (section of the blog)
As a quick aside, if you want some of the awesome qualities of essential oils in a water soluble product, you can add your essential oils using solublizers like polysorbate 20 or PEG-40 hydrogenated castor oil. Do a search for "solubilizer" or look at the label solubilizer or solubilizers to see the experiments I've done with these solubilizers.
In a water soluble product into which you don't wish to add a solubilizer, consider using a hydrosol, which contains the water soluble ingredient of the plant from which the essential oil was derived.
TESTING SOLUBILITY AT HOME
If you want to test if something is water or oil soluble, ask your supplier. If that doesn't help, then get a glass of water and add your ingredient. Mix. Let it sit for a bit at room temperature and see what happens. If it floats to the top or sinks to the bottom and you can see it's a different thing from the water - for instance, it's a white solid or a yellow liquid - that means it didn't mix in and isn't soluble. Do the same for something being oil soluble.
In this picture, you can see the fragrance oil is floating on top of the water in the test tube. This means the fragrance oil is not water soluble. (Oil floats on top of the water as it has a lower specific gravity and is lighter than water. ) If you see this result, you know what you have isn't water soluble!
Join me tomorrow for more fun looking at your comments over the last few weeks!