Almost nothing in a perfumer's organ is smelled neat. Materials are diluted into a solvent at a known strength, kept as stock solutions, and evaluated at that strength every time. This is not a formality — it is the single habit that separates a working practice from guesswork, and it is worth setting up properly before you buy your next material.
Why we dilute
There are four reasons, and they compound.
You can actually smell the material. Most aroma chemicals neat are so concentrated that your nose registers intensity rather than character. A strip dipped in neat gamma-decalactone reads as a flat wall; at 10% it opens into peach, coconut, creamy lactonic warmth. Powerful materials neat will also fatigue you within seconds and cost you the rest of the session.
You can weigh it accurately. A formula might call for a material at 0.05% of the total. In a 20 g batch that is 10 mg — right at the edge of what a milligram balance handles reliably. Dose the same material as a 1% solution instead and you weigh 1.000 g, which any balance does perfectly.
You can compare like with like. Two materials smelled at different strengths cannot be meaningfully compared. If every stock bottle on your bench is at 10%, every comparison you make is a fair one.
It is safer and cheaper. You handle far less neat material, and a 5 g bottle of something expensive becomes 50 g of usable working stock.
Dilute in weight percent (% w/w), not volume. Perfumery materials range from about 0.85 to 1.4 g/ml, so volume percentages are not comparable between materials and will not scale. Every number on this page is w/w.
Choosing a solvent
The solvent is not neutral background — it affects how the material evaporates, how long the stock lasts, and what you can use the dilution for. Most benches end up with two: DPG for stock solutions, and perfumer's alcohol for anything judged the way a finished fragrance would be.
| Solvent | Best for | Trade-offs |
|---|---|---|
| DPG Dipropylene glycol, fragrance grade |
The default for stock dilutions of aroma chemicals. Effectively odourless, very stable, strong solvent power, inexpensive. | Non-volatile, so it never leaves the strip. Dry-down reads slightly muted and damp. Not suitable as the carrier in an alcoholic fragrance. |
| Perfumer's alcohol Denatured ethanol, e.g. SDA 40-B |
Evaluation that should behave like a real fragrance; diluting naturals; anything destined for a finished composition. | Evaporates fast, so top notes read honestly but strips dry quickly. Regulated and taxed in some countries. A few esters and acetals slowly shift in ethanol over years. |
| IPM Isopropyl myristate |
Materials that dissolve poorly in DPG — some resins, absolutes and waxy solids. Oil-based and roll-on work. | Has a faint fatty character of its own. Oily on the strip. |
| TEC Triethyl citrate |
An odourless alternative to IPM with more polarity; good for oil-based products. | More expensive than DPG, slightly viscous. |
| Benzyl benzoate | Resinoids and difficult absolutes; also acts as a mild fixative. | Not odourless — faintly balsamic. It is a declarable fragrance allergen, so it counts toward your regulatory maths. |
| Jojoba or fractionated coconut | Natural and oil-based perfumery, skin application. | Poor for evaluating volatiles; blunts the top. Coconut MCT can go rancid; jojoba is stable. |
If you are buying one solvent to start with, buy DPG. If you are buying two, add perfumer's alcohol.
Standard working strengths
Keeping to a small set of standard strengths means you never have to recalculate what you are smelling. Use 10% as the default and step down only for materials that demand it.
| Strength | Typical materials | Notes |
|---|---|---|
| 10% | Most citrus and floral oils, woods, Hedione, Iso E Super, linalool, most musks, the majority of the catalogue. | The general working standard. Readable on a strip, easy to weigh, safe to compare. |
| 1% | Aliphatic aldehydes (C-8 through C-12), indole, styrallyl acetate, p-cresyl esters, most pyrazines, oakmoss absolute. | Anything that dominates a blend at a fraction of a percent. At 10% these will simply overwhelm you. |
| 0.1% | Damascones and damascenone, Calone, methyl octine carbonate, cassis bases, civet-type materials. | Made by serial dilution from the 1% stock. Still unmistakably present on a strip. |
| 0.01% and below | Thiols and other sulfur materials — grapefruit mercaptan, blackcurrant thiols. | Handle neat only briefly and with ventilation. A spill at neat strength can make a room unusable for days. |
When a supplier or a formula quotes a percentage, it means neat material unless it says otherwise. Get into the habit of writing which you mean every single time — "damascone alpha 1%" and "damascone alpha at 1% of the formula" are wildly different things, and the difference is a ruined batch.
The arithmetic
Two numbers, one subtraction.
Material = batch size × (strength ÷ 100)
Solvent = batch size − material
For 20 g of a 10% solution: 20 × 0.10 = 2 g of material, and 20 − 2 = 18 g of solvent.
A common error is adding solvent to the full amount of material rather than making up to a total — 2 g of material plus 20 g of DPG is a 9.09% solution, not 10%. Always work to a target total weight.
How much to make: less than you think. A 10% dilution used at a few percent of a 10 g trial disappears very slowly. For a material you are still getting to know, 10–20 g of stock is plenty and will stay fresher than a bottle you take three years to finish.
Procedure
- Label the empty bottle first. Name, strength, solvent, date. Doing this before you pour means you can never end up with an unidentifiable bottle.
- Tare the bottle on the balance. Cap off, bottle on the pan, press tare.
- Add the neat material to target weight. Use a pipette dedicated to that material. Record what you actually hit, not what you aimed for.
- Add solvent up to the total. If you overshot the material slightly, add proportionally more solvent to hold the ratio.
- Cap and mix. Swirl or invert for a minute. Solids and viscous materials may need to stand overnight before they are fully in solution.
Serial dilutions
To go below 1%, dilute from a dilution rather than trying to weigh microscopic amounts of neat material. Each step is a tenfold reduction:
10 g of 1% from a 10% stock: weigh 1 g of the 10% stock, add 9 g of solvent. The 1 g of stock contains 0.1 g of neat material, which in 10 g total is 1%.
10 g of 0.1% from that 1%: 1 g of the 1% stock plus 9 g of solvent. And so on.
Every step multiplies whatever error you made in the previous one, so weigh carefully and mix thoroughly before drawing the next sample. Three steps from neat is about as far as you should go before the numbers stop meaning much. If you need 0.001%, make a fresh 0.01% and go one step, don't chain five dilutions together.
Solids and thick materials
Crystalline materials — vanillin, coumarin, ethyl maltol, Ambroxide, cyclopentadecanolide — will not dissolve by shaking alone.
- Warm the solvent, not the material. Stand the capped bottle in a bath of hot tap water for ten to twenty minutes. Do not heat directly, and keep ethanol well away from any flame or hotplate — warm water, off the heat, is all you need.
- Break up the crystals before adding solvent. Large lumps take days.
- Give it time. Many solids need to stand overnight. Check the next morning before assuming it has failed.
- Switch solvent if it will not go. Some materials that resist DPG dissolve readily in ethanol or IPM.
- Watch for it falling back out. If a cold bench brings crystals back out of solution, the dilution is saturated — remake it weaker, or accept that it needs warming and a shake before each use. Never dose from a bottle with crystals sitting in the bottom; the liquid above them is no longer the strength on the label.
Thick resinoids and absolutes are easier: warm gently, and give them a solvent they like. Labdanum and benzoin behave much better in IPM or ethanol than in DPG.
Labelling and storage
A bottle without a full label is a bottle you will eventually pour down the sink. Every stock solution should carry:
- Material name — the same name you use in your formulas, spelled the same way
- Strength as a percentage, with w/w written out
- The solvent
- The date you made it
- The lot or batch of the neat material, if your supplier gives one
Store in amber or dark glass with a tight, solvent-resistant cap. Avoid rubber-bulb droppers for long-term storage — the rubber degrades and adds its own note. Keep bottles filled fairly full; headspace air is what oxidises the contents. Cool, dark, upright, away from radiators and windowsills.
As a rough guide to shelf life: DPG dilutions of stable synthetics last for years. Ethanol dilutions are similar, though a few esters and acetals shift slowly. Citrus oils and other terpene-rich naturals oxidise fastest — six to twelve months, and refrigeration genuinely helps. Oxidised citrus smells thin and slightly turpentine-like; when you notice that, remake it rather than working around it.
Common mistakes
- Measuring by drops. Drop size varies with viscosity, temperature and pipette. It is not reproducible, and it does not scale — see our guide on measuring formulas by weight.
- Reusing pipettes between materials. A trace of a powerful material in a pipette will contaminate everything it touches afterwards. One pipette per material per session, and label them.
- Making far too much. Litre bottles of 10% stock are a beginner's expense and an oxidation problem.
- Comparing across strengths. If you are asking which of two materials is stronger, they must be on identical strips at identical dilution.
- Not writing it down. The bottle records the strength; your notebook should record the date, the lot, and anything odd about how it behaved.
- Diluting everything at once. Dilute what you are studying now. Materials keep better neat than in solution.
Once your stock solutions are set up and consistently labelled, the rest of the practice gets much easier — you can go straight from opening the bench to smelling, and your formulas become reproducible. The natural next steps are learning to compound by weight and building a proper evaluation routine so that each dilution you make actually teaches you something.