The Spatial Sillage Lab

Illustrative model, not a measurement A modeled concentration field around a wearer, for learning how spray, concentration, warmth, moving air and movement shape a trail. Every constant is an assumption; nothing here is measured, and it says nothing about what a nose would notice.

The drawn field needs JavaScript, which is off or has not loaded. Everything the drawing shows is in the tables below: the field at five set points for eight settings, and the assumptions behind it.

The model, and every assumption in it

1. The room is a floor plan. The air is taken as evenly mixed from floor to a 2.5 m ceiling, so only the plan is drawn. Three rooms: a small room, 4 × 3 m; an office, 8 × 5 m; a hall, 14 × 9 m.
2. What is sprayed. Each spray is 0.1 mL, the figure the site’s decant calculator starts from (sprayers vary). The share of perfume oil is the midpoint of the band in the site’s concentration table (perfumery convention): eau de Cologne (2–5 %) → 3.5 per cent; eau de toilette (5–15 %) → 10 per cent; eau de parfum (15–20 %) → 17.5 per cent; parfum / extrait (20–40 %) → 30 per cent.
3. Volatility classes. The oil is split into top, heart and base by the teaching accord’s modeled shares. A component’s class comes from its record: the accord component’s volatility, else the molecule record’s volatility class, else its role in the accord; a component with none of these is modeled as heart, and the page says so beside it.
4. Leaving the skin. Each class evaporates at a steady fraction of what is left (first order). The half-lives are the site’s relative-evaporation constants (the volatility simulator, data/1b/volatility.json, which says they “were chosen for the simulator and are not measurements”), the median of each class: top 2.25 h (Limonene 1.5 h, Linalool 3 h), heart 7 h (Hedione 6 h, Coumarin 8 h), base 13 h (Vanillin 10 h, Ambroxan 12 h, Iso E Super 14 h, Muscone 16 h).
5. Temperature. An assumed rule of thumb: evaporation doubles for every 10 °C above 20 °C and halves for every 10 °C below. Skin temperature, clothing and the skin itself are not modeled (the essay on skin covers what is known).
6. In the room. The modeled concentration spreads by an effective mixing coefficient (the stirring of indoor air, far faster than molecular diffusion), drifts with the air from the window side to the door, and is removed by air changes: still air (windows shut): mixing 0.003 m²/s, drift 0 m/s, 0.5 air changes an hour; a gentle draught (window to door): mixing 0.006 m²/s, drift 0.05 m/s, 1.5 air changes an hour; ventilated (window and door open): mixing 0.012 m²/s, drift 0.15 m/s, 4 air changes an hour. All of these are assumptions chosen for illustration, not measurements of any room.
7. Numbers. A grid of cells of about 0.17 to 0.22 m, explicit finite differences, upwind drift, a time step inside the scheme’s stability limit. Results are relative: 1 is the reference (the rose teaching accord, an office, still air, 20 °C, eau de parfum, 4 sprays, the wearer seated) 0.5 m from the wearer after 10 minutes. The bands halve, down to 1/32.
8. What it does not say. Whether anyone can smell it, at what distance a scent is noticed, or how strong it seems: odour thresholds of mixtures are not on record here, and perception is not concentration. A shape to think with, not a prediction for your room.

The accords, by volatility class

The teaching accords are the house’s, for learning: modeled proportions, not a recipe, not for skin. Their classes, as the model reads them:

Eight settings, read at five points

The same model, run at build time for eight settings and read at the set points: A, B, C and D at 0.5, 1, 2 and 3 m from the wearer’s seat towards the door, E in the far corner. This is the drawing’s text equivalent.

The reference

A rose, from four molecules; an office, 8 × 5 m; still air (windows shut); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

A gentle draught

A rose, from four molecules; an office, 8 × 5 m; a gentle draught (window to door); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

Ventilated

A rose, from four molecules; an office, 8 × 5 m; ventilated (window and door open); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

A warm room, 30 °C

A rose, from four molecules; an office, 8 × 5 m; still air (windows shut); 30 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

A small room

A rose, from four molecules; a small room, 4 × 3 m; still air (windows shut); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

A hall

A rose, from four molecules; a hall, 14 × 9 m; still air (windows shut); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer stays seated.

The wearer leaves after five minutes

A rose, from four molecules; an office, 8 × 5 m; still air (windows shut); 20 °C; eau de parfum (15–20 %), 4 sprays; the wearer walks across the room in five minutes, then leaves.

The cologne accord, eau de Cologne, 2 sprays

A cologne; an office, 8 × 5 m; still air (windows shut); 20 °C; eau de Cologne (2–5 %), 2 sprays; the wearer stays seated.

Read the essay on skin · The projection calculator · The volatility simulator · The Olfactory Genome · The teaching accords

This page’s data is published under CC BY 4.0: /data/labs/sillage.json.

version 1 · updated 2026-09-30