Simply - Viscosity is the how thick or thin the consistency of any liquid. In aromatherapy, it has a lot to do with how easily essential oils will pour.
When we are talking about essential oils, this can be very important especially when it comes to measuring. As the viscosity – how thick or thin an essential oil is, will and can, make a world of difference in how you blend them, what oils you are able to blend together (or not) and how long they will last when being diffused.
Essential oils can be thin like water or alcohol. These pour easily and likewise, evaporate quickly, causing them to be added, in wrong amounts.
Essential oils can also be thick like honey.
Occasionally you will come across one that is so thick it is like a paste. It will not pour at all – unless heated. We see this more with absolutes than with true distilled essential oils.
Mainly when blending but also when diffusing. As some diffusers work better with thinner blends. Yet others will last longer with a thicker blend.
If you were to compare the drops of say, Lemon oil, with that of Vetiver and were to drop 5 drops of each on a clean glass plate, you would see the 5 drops of lemon would spread out easily and be flat and run quickly across the plate if tipped on edge.
The 5 drops of Vetiver could possibly stay in a little bit of a mound and would move very slowly across the plate and then only if tipped for a longer amount of time.
Thicker oils are harder to get to blend well into or with lighter oils.
This is the same thing that can happen when you try blending essential oils with carrier or fixed oils when used for massage. You may need to stir or gently shake your massage blend to incorporate all the essential oils in a more uniform end product.
Because the Thinner lighter oils have a tendency to evaporate quickly and the thick honey like ones will linger or take days to evaporate you want to incorporate both viscosity types in your blends.
Often times you will hear aromatherapists talk about ‘base’ notes. They are usually the thicker more viscose essential oils and they will help ‘hold’ your lighter scented oils to help make your scenting last for longer than a few hours.
In two different ways:
First, the quantities involved. Not so much a problem when you a making a small amount of a massage oil such as for one time use (1/2 oz or less) but when you are making LARGE batches you can have quite a discrepancy in the potency.
That’s why when we give you recipes they are made in small – typically one or 2 ounce quantities as the amount of essential oil is very small and the strength will be fairly consistent.
If you were to make large quantities, your blend may not smell or react the same. The quantities of essential oils will not be the same due to the varying viscosities of essential oils when measured in drops.
Take for example if you were to measure 1 mL of Lemon oil and count the drops out of your pipette you would count about 25 drops but the same 1 mL of patchouli may only count out to be 18 drops. So thickness (viscosity) can count.
When mixing larger quantities you will be measuring by volume, typically in mL’s, not by drops. Or, the other method of measuring essential oils is by weight. Not practical for the everyday user but a must for those that need a blend to be exactly the same from batch to batch. Since we are here for the everyday user we will not delve into the weighing of essential oils.
Most of the recipes we share are proportional and can easily be made larger but not too large if you continue to measure in drops – your final product will be quite different. So, to increase many recipes you will need to do conversions or use a graduated device. Many pipettes have graduation marks so you may want to have some of those on hand for blending larger amounts.
Another reason why viscosity is important: if you are to make a blend for diffusing or adding to potpourri or candles, etc. you will want to blend thick, viscous oils with lighter, thinner oils.
What that does is to help your lighter, thinner oil last longer as the thicker oils will ‘trap’ some of the lighter oils molecules and only release them as the thicker oils evaporate. This will help protect the more highly volatile oils – such as orange and lemon, to be enjoyed in your blends for more than an hour or two.
In conclusion, when blending, think of the viscosity too, not just the oils you are using but how they will be used, how long they need to last and how large of batches you will be making of your final product.
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