Dilution and writing formulas

Weighing in grams, 10% and 1% dilutions, parts and per-mille math

Fisfis Academy · 14 min read ·

Dilution and writing formulas

What you will learn

  • Explain why we work in grams rather than drops
  • Prepare 10% and 1% dilutions of a material correctly
  • Write a formula in parts, per mille (‰) and percent, and convert between them
  • Calculate the actual (neat) amount of a material added as a dilution

A perfume formula is less like a cooking recipe and more like a prescription: how much of each material is used has to be written down in a way that can be repeated. A formula you cannot repeat, however good it smells, is an accident that happened once.

Grams, not drops

Drops sound practical, but they are not reliable. The weight of a drop changes with the material’s density and viscosity and with the tip of the pipette: drops of a thick resin and a thin citrus oil are not the same. That is why professional labs write and weigh formulas by weight (in grams).

A precision scale is the heart of the workshop: each material is weighed in grams, one after another.
A precision scale is the heart of the workshop: each material is weighed in grams, one after another.

Working in drops

  • Drop weight varies with the material and the pipette
  • The same formula never gives the same result twice
  • Scaling up (e.g., from 10 g to 100 g) magnifies errors
  • Only usable for rough first trials

Working in grams

  • Repeatable results with a 0.01 g scale
  • The formula converts directly to percent and per mille
  • Scaling up is simple multiplication
  • Checking IFRA limits becomes possible

Why do we dilute?

Many fragrance materials are so powerful neat that even a few milligrams can throw off the balance. On a 0.01 g scale, the smallest amount you can weigh is already 10 milligrams. If you dilute the material beforehand to 10% or 1%, you can make adjustments 10 or 100 times finer on the same scale. Dilution also turns solid materials (e.g., vanillin, coumarin) into liquids and makes smelling easier.

  1. Weigh the bottle and tare Place a clean, labeled glass bottle on the scale and tare it (zero it). Have your gloves and goggles on.
  2. Add the material For a 10% dilution, weigh 1.00 g of material. Add it slowly with a pipette; if you overshoot, do not take any back out, recalculate the target instead.
  3. Top up with solvent Add perfumer’s alcohol or DPG until the total reaches 10.00 g (that is, 9.00 g of solvent). For a 1% dilution, bring 0.10 g of material up to 10.00 g.
  4. Mix and let it dissolve Cap the bottle and shake gently. Wait until solid materials have fully dissolved; if needed, hold the bottle in warm water (never over a flame).
  5. Label and record Write “Material – 10% – alcohol (or DPG) – date” on the label. Note the same information in your notebook.

Alcohol or DPG?

Perfumer’s alcohol (ethanol)

  • Evaporates quickly and opens the scent on paper and skin
  • The main carrier of the finished perfume
  • Highly flammable; must be kept tightly closed
  • Dilutions can slowly evaporate and become more concentrated over time

DPG (dipropylene glycol)

  • A nearly odorless, slow-evaporating solvent
  • Dilutions keep their concentration for a long time
  • Does not ignite as easily as alcohol
  • Can make a scent seem “heavier” on paper; not the main solvent for spray perfume

Materials usually used diluted

  • Aldehydes: Sharp and fatty when neat; at 1%, a soapy, bright sparkle.
  • Galbanum: Green, bitter and extremely diffusive; even a few milligrams are noticeable.
  • Vanillin: A crystalline solid; once dissolved, a sweet, creamy vanilla.
  • Labdanum: A dark, sticky resin; when diluted, warm leather and amber tones.
  • Oakmoss: Damp forest floor and ink; very strong and restricted by IFRA.

Writing the formula: parts, per mille, percent

Formulas are usually written in parts: “Bergamot 30, Rose 20, Patchouli 10” means these materials are in a 30:20:10 ratio by weight. If you bring the total to 1000, each number becomes a per mille (‰) value directly; bring it to 100 and it becomes a percent. The per-mille system is common because it lets you write small amounts without decimals.

Be careful when calculating a material added as a dilution: if the formula says “Galbanum 10% – 20 parts,” the concentrate actually contains 2 parts of neat galbanum. When you check IFRA limits, you always use this neat amount.

  • 1 : 9 10% dilution: 1 g material + 9 g solvent
  • 1 : 99 1% dilution: 0.1 g material + 9.9 g solvent
  • ‰ Per mille: a formula written so the total is 1000 parts
Dilution
A material thinned to a set ratio in a solvent (e.g., 10% in alcohol).
Tare
The weight of the container; zeroed on the scale so it is subtracted from the weighing.
Part
The unit that expresses the weight ratio between materials in a formula.
Per mille (‰)
A material’s share in a formula whose total is taken as 1000.
Concentrate (oil)
The blend of all the fragrance materials before it is diluted with alcohol.
DPG
Dipropylene glycol; an odorless, slow-evaporating solvent commonly used for dilutions.

Key points

  • Formulas are written in grams, not drops, and weighed on a 0.01 g scale.
  • A 10% dilution is 1 g material + 9 g solvent; a 1% dilution is 0.1 g material + 9.9 g solvent.
  • Parts, per mille and percent are different ways of writing the same ratio; making the total 1000 simplifies the math.
  • Calculate the neat amount of any material added as a dilution; IFRA checks are based on the neat amount.
  • Never heat ethanol over a flame; label every dilution with its ratio, solvent and date.

Sources

  • Curtis, T. & Williams, D. G. (2001). Introduction to Perfumery (2nd ed.). Micelle Press.
  • Calkin, R. R. & Jellinek, J. S. (1994). Perfumery: Practice and Principles. Wiley.
  • Arctander, S. (1969). Perfume and Flavor Chemicals (Aroma Chemicals). Montclair, NJ: published by the author.
  • Aftel, M. (2001). Essence and Alchemy: A Book of Perfume. North Point Press.
  • IFRA (International Fragrance Association). IFRA Standards and guidance on the IFRA Certificate of Conformity.