Updated: Apr 5, 2018
Las posting (click here if you did not read part 1) we started with this fascinating system and hopefully you are already hooked or at least a bit curious about it and you want to know more. Well, here is more. A LOT more:
When we smell a material, what is it that we are smelling? Is the material itself? Is it its strength? Nope. Basically we are smelling its surroundings. We are actually smelling the interaction of the evaporating molecules of the material with the air surrounding the sample. This is the reason why there's always a difference between "what we smell" and "what the smell is". This odor in the air surrounding the material is what its called in perfumery Headspace. (Ah!!!, that was it?)
Now, that being explained, let's jump straight into the concept of relative impact: once we have determined the type of smell by matching it with a letter of our alphabet, and after creating its odor profile (what we did in the first part), we need to establish what the impact of the smell is, how “strong” the odor is. We call it relative impact because this impact will be a number relative to a predefined standard or reference material: linalool synthetic. Why Linalool synthetic, you might ask? well, because it is “readily available, is one of the most abundantly used raw materials in perfumes and flavors and because the quality from the major suppliers does not vary greatly (Linalool from natural sources is not suitable). In terms of its impact it falls about midway in the range of materials used by the perfumer.” (From “Training the ABC's of Perfumery” by Stephen V. Dowthwaite, PerfumersWorld. Paper published in modified form in Perfumer & Flavorist, Allured Publications, USA 1999).
Linalool, as a standard, will have a value of a 100. Anything “stronger” will have a bigger value while anything weaker will have a smaller one.
How do we determine a relative impact value?:
Lets put 1 drop of linalool (Letter L in our ABC) on a smelling strip and a drop of let's say, PEA (phenyl ethyl acetate) (letter R in the ABC) in another.
Now, with 1 sample in each hand smell quickly the linalool first and the PEA right after. The whole idea here is not to smell the odor itself but to analyze how strongly the headspace hits your nose. If you find yourself "thinking" about the smell, you've missed it already, you've passed the point of impact evaluation. Try again.
Now, if linalool is a 100, is PEA more or less? if it is more, how much more?, what number do you think it should be? what about if it is less? the same question, what number? 30?, 60?, 85?
As an average, people find it to be a 60. But DO NOT be discouraged if you thought of a different number. Everything WILL work out if you are consistent.
Now you have determined the relative impact value of 2 materials, so you can use ANY of the 2 as a reference. Put a drop of Sandalwood oil (letter W) in a smelling strip and analyze its impact. You'll soon realize that it is even lower than PEA. You could have compared it with your linalool OR with your PEA, doesn't matter. what's its value? Probably around a 1/4 of the linalool (25) or about half the PEA (30). Let's say 25.
Now, let's try to evaluate a drop of Cis-3-Hexenol (ABC: G). Go ahead, Put a drop in a blotter. You smell first the Linalool and then the Cis-3 Hexenol. The second it hits your nose you automatically realize its impact is higher, a LOT higher. The problem is...how much? See? It is easy for our noses to compare materials within certain range. But when this range is to wide then it becomes really difficult to quantify. What to do, you might be wondering? Easy!, we dilute! Let's dilute the Cis-3 Hexenol at 10% in DPG (Dipropylene Glycol), IPM (Iso-propyl myristate), or any other no odorous solvent.
Now compare the 1 drop of linalool with 1 drop of a 10% dilution of Cis-3-Hexenol in the same fashion as you did before. Is it higher or lower than linalool? Lower right? What number would you assign? 70? Let's go with 70 but since this was a 10% dilution, our real relative impact value is 700 (because we only smelled a 10% of it). Let's keep rolling!
What about even HIGHER relative impact values? Well, now we can use the 700 (undiluted Cis-3 Hexenol) as a reference! Let's try 1 drop of Iso amyl acetate in a blotter. Do it quickly because it evaporates REALLY fast (we will get into the time line later on). So compare your 100% Cis-3 Hexenol with the Iso amyl acetate. Higher, right? How much? Do we agree in around 1200? One way to double check: put 2 drops of Cis-3 Hexenol (that should be 700+700=1400) and compare with 1 drop of Iso amyl acetate. Is it lower or higher now? If we said 1200 it should be lower. Capisci?
Let's make a little table of the values we got so far:
At the beginning you will be assigning values and you will not be sure how accurate they are. The process of assigning numerical values as a relative impact it might look too subjective but there is a way to check the accuracy and consistency of the measurement, which is also extremely related with the concept of accord.
What is an accord?
It is the mix of few materials (not many, just 2, 3 or 4) in a proportion such that none of them can be identified or smelled individually. If I mix "x" amount of material A and "x" amount of material B and I smell the result without being able to smell neither A or B but only a "new" smell, then I have in front of me an accord.
Theoretically you can create an accord by mixing ANY materials, whether they are useful or not, that's another matter.
There's a lot of confusion here since a lot of places and even perfumers use terms like "Leather accord", or "Rose accord". Those are not actually accords but compounds, specialty bases, blends or mixes (Oh, Jeezz..I can hear them already).... An accord does not need to smell like something. It is a "useful" smell in itself that is usually used as a building block for a perfume. It is more often associated with ideas rather than things, like "summer rain" or "urban sadness" or it has no name whatsoever like the accord used in Ninna Ricci's perfume, L'air du Temps (benzyl salicylate, Ylang ylang, eugenol & musk ketone).
The traditional way to create an accord takes time. A LOT of time. Basically you have to mix different materials in different proportions to find that exact sweet spot that you cannot smell any of them individually and you have a brand new smell.
Let's try the example with L'air du Temps accord just mentioned: You would need to mix a lot of samples: In one pot (or whatever you use for mixing) 1 drop of Benzyl salicylate and 9 of ylang ylang; in another pot: 2 drops of Benzyl salicylate and 8 of ylang ylang; in another one: 3 of Benzyl salicylate and 7 of ylang ylang and so on till you do this:
And now you analyze each of the samples and look for the one that you cannot smell neither of the 2 materials. soon you realize that that sweet spot is somewhere between 8/2 and 9/1. Oh, no!, What to do? Oh, easy: We dilute! And start the thing again but this time, you will find the spot between 8.6/1.4 and 8.7/1.3:
Good news is that it IS possible. Bad news is that these are only 2 materials and you need to analyze all the possible combinations between FOUR materials, and since we are talking geometric multiplication here...that is NOT something you want to do unless you have the next 6 or 7 months free and an impressive amount of patience at your disposal (this by the way, is the way that is done at the big houses, where the first year you don't make perfumes: you just....make accords...voilá!).
There ARE really good news though: Using the ABC you can do it so much easier...and faster. We will use the concepts of Headspace, accord and relative impact value that I've already explain. Let's see:
First of all, when we talk about an accord we talk about something that is happening in the headspace (remember that we smell the headspace, not the actual material)
So, if we have the relative impact values of the materials we are trying to make an accord with, by applying a little math, we could make the accord literally in minutes instead of months. How?
Even though YOU CANNOT change the relative impact of a material you CAN change the amount of material used to increase or decrease its impact. Basically we will try to make the relative impact value of every material in the accord equal to 100 by modifying the amount of material used. And if every material in the mix has the same impact (100 or any value, as long as all are the same) then we won't be able to individualize any material by itself and, oh!, what a coincidence! That is exactly what an accord is!
Let's continue with the materials of the L'air du Temps accord: The relative impact value of benzyl salicylate is 15. How many times I have to increase the benzyl salicylate so it has an impact of 100? or, let's ask it differently: How many times an odor impact of 15 fit in a 1oo? Easy!: We divide 100 by 15 = 6.67. Ylang ylang: Relative impact is 120, so 100/120=0.83. Let's put everything in a table:
What this means is that if we put 6.67 parts of benzyl salicylate, 0.83 parts of ylang ylang, 0.91 parts of eugenol and 5 parts of musk ketone we obtain the accord L'air du Temps, a brand new smell, where we cannot smell individually any of its components. "Parts" refers to whatever you use as measurement: grams, kilos, drops, etc.
Is my relative odor impact correct? Double checking.
Another way to calculate the relative odor impact value is with the Technique of the pots and drops. Lets calculate Hydroxycitronellal: You put in a pot one drop of linalool and 1 drop of Hydroxycitronellal. Smell quick and determine which one has a higher value (linalool in this case). Now, start adding, 1 drop at a time, the material that has a lower impact in your first sniff, smelling in between to see if you can still identify both smells. At 5 drops of Hydroxycitronellal you will have reach that point, and then you can conclude that the actual relative odor impact value of the Hydroxycitronellal is 20 (or 1/5 of linalool).
Let’s try another one: Linalool and Phenylacetic Acid. Drop 1 part of Phenylacetic Acid and…how many parts of Linalool you will need to balance the smell? Probably around 4. That means that the Relative impact of Phenylacetic Acid is 400, or 4 times the impact than Linalool (100).
As I said before, this process might sound subjective but once you can smell that balance where none of the two materials becomes apparent, you are on the right track. In time you will realize that what you though was subjective is nothing but a perfect mathematical equation and plays an important role when you have to increase or decrease the smell of one material in a mix. It will give you a measurable idea of how much you need to go up or down to manipulate correctly the headspace.
Using this method, we can infer that since…
· Phenylacetic Acid has 4 times the impact of Linalool and
· Hydroxycitronellal has 1/5 of the impact of Linalool then
· Phenylacetic Acid has 4 / (1/5) = 20 times the impact of Hydroxycitronellal.
This way calculations between different materials are easier and we don’t need to rely on true threshold or vapor pressure values, which are so expensive, time consuming and difficult to calculate.
Well, I think this was a lot of information for this second post. For now probably you have enough to think, evaluate and practice till the third part, next week.
Remember that The Art and Technology of Perfumery Foundation + Course will be held April 23-27 at the Perfumer's Studio in LA, California for the very first time translated to Spanish. Let this be known to anybody that might be interested!
Also, in case you didn't, check the Goodies section of the site for any other extra useful info.
As usual, if you enjoyed, or did not, have questions or corrections or just want to vent or ramble, please, leave a comment.
Have a wonderful week!