Why Pre-Dilute? Balance, Nose and Consistency
Your formula contains a molecule at 0.2%, and you are preparing a 10 gram trial. The amount you need to weigh is 0.02 grams. Most laboratory balances will "read" this value but cannot weigh it reliably. Pre-dilution removes the problem: you take the molecule into a 10% stock solution beforehand and weigh 0.2 grams.
There are three reasons for pre-dilution. Weighing accuracy: small doses are brought into the balance's safe range by dilution. Smelling: powerful molecules that overwhelm the nose when neat (aldehydes, indole, Javanol, cis-3-hexenol) show their true character only when diluted. Consistency: two people working from the same stock solution get the same result; a recipe of "two drops" gives two different results in two different hands.
In professional perfumery, formulas are very often written with dilutions: the formula line reads "Javanol 10% DPG — 3.0", and this means 0.3 grams of pure Javanol.
Which Raw Material at Which Ratio: 1%, 10%, 50%
The ratio is chosen according to the strength of the molecule and its typical dose in the formula. The aim is to bring the amount to be weighed in the formula above 0.1 grams.
| Stock ratio | Which raw materials | Typical examples |
|---|---|---|
| 1% | Very powerful molecules used at trace doses | Indole, skatole, cis-3-hexenol, pyrazines, sulphur molecules, aldehyde C-12 MNA, nootkatone |
| 10% | Low-to-medium dose molecules with strong character; solid raw materials | Javanol, Ebanol, calone, ethyl maltol, vanillin, coumarin, heliotropin, damascones, Iso E Super (for evaluation) |
| 50% | Viscous or solid materials that are nevertheless used at high doses | Resins (benzoin, labdanum), absolutes, Galaxolide (most commercial grades are already sold at 50% in BB/DEP), Ambroxan |
| Neat | High-dose liquid raw materials | Linalool, linalyl acetate, Hedione, dihydromyrcenol, benzyl acetate, cedarwood, bergamot |
Ratios are by weight (w/w). "10%" means 10 grams of raw material in 100 grams of solution; you add 9 grams of solvent to 1 gram of raw material, not 10 grams. The distinction looks small, but the difference between 10% and 9.1% turns into a noticeable deviation once the formula is scaled up.
Solvent Choice: DPG, Ethanol, IPM, TEC and Benzyl Benzoate
The solvent is chosen according to the product the stock solution will go into. The wrong solvent carries an unwanted component into the formula.
| Solvent | Where it suits | Watch out |
|---|---|---|
| DPG (dipropylene glycol) | General purpose; alcohol-based perfume, most cosmetic bases | Evaporates slowly; at high levels it weighs the formula down. May be incompatible in candle and oil-based products |
| Ethanol (96%) | Evaluation strips, stocks for alcohol-based perfume | Volatile; the stock concentrates over time. Close the cap tightly on a frequently weighed stock |
| IPM (isopropyl myristate) | Oil-based perfume, roll-ons, candles, some cosmetics | Can cause clouding at high levels in alcohol |
| TEC (triethyl citrate) | Cosmetic-compatible stocks where low volatility is wanted | Expensive; viscous |
| Benzyl benzoate | Resins, musks, solid crystals | Has a slight odour of its own; enters the allergen declaration |
The rule is simple: the solvent of the stock solution should be a substance that is already present in the finished product, or whose presence does no harm. For alcohol-based perfume you choose DPG or ethanol; for candles, IPM or a carrier directly suited to wax; for water-based products, a solvent compatible with the solubiliser system.
Preparing a Stock Solution: Step by Step
A stock solution is prepared as carefully as the rest of the formula; otherwise every formula carries that stock's error.
- Decide the target amount and ratio
Example: 10% Javanol, 20 grams. Raw material 2.0 grams, solvent 18.0 grams. Prepare small volumes; stocks change as they sit.
- Tare the bottle, weigh the raw material
Place a dark glass bottle on the balance and tare it. Weigh the raw material directly into the bottle; there is no transfer loss. For solids, add to the bottle with a small spatula.
- Add the solvent by weight
By weight, not by volume. Add solvent up to the target total weight. Dissolve solid raw materials in a warm water bath while stirring.
- Label
Raw material name, ratio, solvent, preparation date, prepared by. The format "Javanol 10% DPG 03.10.2026 ZB" is enough. An unlabelled stock is the most dangerous bottle in the workshop.
- Record
Write it in the stock book or file: from which raw material lot, with which solvent lot it was prepared. When a lot changes, this is where you catch the difference.
- Store and set a shelf life
Cool, dark, tightly capped. 1% stocks should be refreshed within 6 months, 10% stocks within 12 months; citrus and aldehyde stocks have a shorter life.
Accounting for Dilutions in the Formula and Frequently Asked Questions
When a dilution is used in a formula there are two separate numbers: the amount weighed and the amount of pure substance. A formula that does not separate the two comes out wrong in the IFRA calculation and in costing.
| Formula line | Weighed | Pure substance | Solvent contribution |
|---|---|---|---|
| Javanol 10% DPG | 3.0 g | 0.3 g | 2.7 g DPG |
| Indole 1% DPG | 0.5 g | 0.005 g | 0.495 g DPG |
| Benzoin 50% BB | 4.0 g | 2.0 g | 2.0 g benzyl benzoate |
Show the total solvent coming from dilutions as a separate line at the end of the formula. Knowing that 15 grams of DPG in a 100 gram concentrate comes from dilutions lets you read both the IFRA calculation and the perceived intensity of the scent correctly.
Can I prepare a stock solution by volume?
What should I do if I don't know which solvent to choose?
How long does a dilution keep?
Can I apply heat when dissolving a solid raw material?
Should I write the formula neat or with dilutions?
Does the dilution itself change the scent?
Are there raw materials sold commercially in diluted form?
What is the most common mistake when preparing a dilution?
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