In this post I’m setting out the way in which I go about making a blend - including how to dilute the materials first to facilitate blending.
This is because these are two questions I get asked by people starting out in making their own perfumes quite often.
First I dilute all my ingredients in ethanol to 10% or in a few cases less (there are notes on the individual ingredients on the post suggesting a starter kit where I think you need to dilute more).
This means you are going to need lots of bottles to make the dilutions in - I use standard 30ml or 50ml amber or cobalt blue bottles to protect the mixture from the light. For details of other things you are likely to find useful have a look at my post on Starting Equipment. To make the dilution you need to follow this procedure:
With ethanol the specific gravity is 0.8, which means you can get about 25 grams into a 30ml bottle, 40grams in a 50ml bottle.
So, to get a 10% solution of your essential oils you first put the 30ml bottle it's going into on the scales (or balance if you prefer) and tare it (so that the display shows 0 with the empty bottle on), then add 2.5grams of your essential oil - don't tare again - top up to 25 grams with ethanol and hey presto! If you find you've put in a little under the 2.5 grams, adjust the amount of ethanol such that you end up with exactly 10 times as much in total, keeping in mind that the bottle will be full at about 25 grams or so, so you don’t want to put in too much of the oil you are diluting.
The process for aroma chemicals and absolutes is exactly the same and of course this process will work when you are dealing with solids just as well as with liquids - the degree of dilution you'll need will vary, but for most I would go with 10%. Exceptions are things like Vanillin (1%) Synthetic Civet (0.1%) and so on. Don’t forget that if you buy an aroma chemical already diluted, e.g. vanillin at 10% in propylene glycol if you dilute it down to 10%, you'll actually have 1% vanillin in a mix of PG and ethanol.
Having done that, you now have nice, easy, mobile liquids to work with in every case.
Before I start blending I make a list of the materials I plan to use and the proportions of each I think will work - this can be guesswork to begin with but over time you’ll get good at anticipating what will work and how much you’ll need, depending on the effect you are seeking.
I then blend using the requisite number of drops of each of the materials I want to work with - weighing each as it goes into the blending bottle, taring between items and making a note of the exact weight that went in and at what dilution. This means that I can replicate the blend later if it turns out to be good, or alter it later if it does not.
I normally build a fragrance in three stages - first blending the base notes together, then the middle notes and finally the top notes. I sometimes do this all in one blending bottle, sometimes in three separate ones and then mix the three elements together later. Either way works but when you’ve made the final blend give it a good shake and then let it sit for at least a day, preferably a week before you evaluate the scent you’ve made as it will change over time - usually getting better.
Producing the Fragrance
Once you have the blend in the proportions you want, you might want to alter the concentration - either increasing it to become and EdP or Parfum strength or reducing it to a typical cologne or EdT strength.
I use a spreadsheet, available for download here, to help me get from one to the other. To make the spreadsheet work you’ll need to record the exact concentration and weight of everything in your sample blend first, then adjust up by adding some items at 100% or 50% for example, until you get the total concentration you are looking for. Adjusting down is simpler - just add ethanol at the top of of the spreadsheet until you have the concentration you want. [in the spreadsheet the teal coloured fields are user-entered numbers, the other calculated from those. The formula provided is a published cologne formula, which is included to illustrate how it works]
The point about blending at 10% (ish) is that it’s easy to work with and evaluate. Production of the final product can be at whatever concentration you like (subject to compliance).