Short answer
A rain accord recreates petrichor — the smell of rain on dry ground — by combining an earthy note with wet, green and mineral ones. The earthy part comes from geosmin, the compound soil bacteria make that humans detect at extraordinarily low concentrations; it must be used in parts per million or less, built up through a chain of dilutions. Around it go watery-ozonic materials such as Calone, green notes for wet leaves, a mineral or "wet stone" effect and a clean woody-musky base. In South Asia a related scent is captured in mitti attar, distilled from baked clay.
What petrichor is
The word was coined in 1964 by two Australian researchers to describe the oily, earthy smell released when rain falls after a dry spell. Several things contribute: oils that plants release onto rocks and soil in dry weather, geosmin produced by soil microorganisms, and ozone carried before a storm. A perfume rain accord stylizes these into three facets — earth, water and air — rather than copying any one of them.
The building blocks
| Facet | Materials |
|---|---|
| Earth | Geosmin (traces); patchouli or vetiver in small amounts; an earthy-mossy material |
| Water and air | Calone (watery, marine); Helional (ozonic, green-floral); aldehydes in traces |
| Wet green | cis-3-Hexenol, violet leaf, galbanum in traces |
| Mineral | A dry, flinty or metallic note; Iso E Super for transparency |
| Base | Clean musks, Ambroxide, pale woods |
The watery materials are covered in aquatic notes in perfumery, where Calone's own dosage trap is explained; green notes in green notes.
Dosing geosmin: a dilution chain
Geosmin is so potent that a recognizable amount in a perfume is a tiny fraction of a percent. It is usually bought already diluted. To work with it, make a chain of dilutions and record each one's strength. An illustrative calculation, by weight:
- Stock A: geosmin supplied as a 1% solution.
- Stock B: 1 g of stock A + 9 g ethanol = 10 g at 0.1% geosmin.
- Stock C: 1 g of stock B + 9 g ethanol = 10 g at 0.01% geosmin.
- Using 2 g of stock C in a 100 g accord adds 2 × 0.01 ÷ 100 = 0.0002 g of geosmin — 2 parts per million of the accord.
Label each stock clearly and keep geosmin, like other trace-powerful materials, away from shared pipettes and benches. The general equation is in the perfume dilution equation, and safe handling of traces in preventing cross-contamination.
An illustrative rain accord
| Material | Parts |
|---|---|
| Iso E Super | 25 |
| Hedione | 20 |
| Clean musk | 15 |
| Calone, 1% in DPG | 10 |
| Helional | 8 |
| Ambroxide, 10% in ethanol | 6 |
| Vetiver oil, 50% in DPG | 5 |
| cis-3-Hexenol, 10% in DPG | 4 |
| Geosmin, stock C (0.01%) | 4 |
| Patchouli oil, 10% in DPG | 3 |
| Total | 100 |
For study only; not tested or safety-assessed. At 4 parts of stock C, geosmin is 4 ppm of the accord; try 1, 2, 4 and 8 parts to find the point where it reads as rain rather than beetroot or cellar.
Mitti attar
In the attar tradition of Kannauj in India, mitti ("earth") attar is made by distilling sun-baked clay into sandalwood oil, capturing the smell of first rain on dry earth. It is a natural reference worth smelling before building a synthetic accord; see what is attar.
Restrictions and records
- Check IFRA Standards and allergen status for each material: Iso E Super ("tetramethyl acetyloctahydronaphthalenes") and patchouli oil are on the EU's expanded declarable list, and Helional's IFRA status should be checked for your category (fragrance allergens list).
- Record each dilution of geosmin as its own material linked to the parent, with its strength and date.
Where these materials sit among the families is mapped in the guide to perfume materials by odor family.
Frequently asked questions
Why does my rain accord smell of beetroot?
Geosmin is also what makes beetroot taste earthy. Too much of it reads as vegetable or cellar; reduce it and bring up the watery and green facets.
Can I make petrichor without geosmin?
You can suggest wet earth with small amounts of patchouli, vetiver and mossy materials, but geosmin gives the unmistakable first-rain note.
Is a rain accord an aquatic?
It borrows aquatic materials but adds earth and green; most perfumers treat it as its own effect.
Written and reviewed by the RUŌOD Lab team. This article is general education about perfume formulation and record-keeping; it is not legal, regulatory or safety advice, and the examples are illustrations, not validated commercial formulas. How we write and check these guides.