In short
A stock solution is a dilution you keep ready, so that small amounts of a material can be weighed reliably. A sensible set uses a few standard strengths chosen by each material's power and your scale's limit. You must also keep account of the solvent every stock adds to a formula.
What you will learn
- Choose stock strengths for a formula
- Calculate the stock weight and solvent carried for each line
- Maintain and retire stocks properly
Before this lesson: Perfume Formula Practice Problems
Choosing a strength
Work backward from what you need. The rule, from your weighing practice, is that the weight on the scale should not fall below your practical minimum.
highest usable stock strength = pure amount needed ÷ practical minimum
Suppose a batch needs 0.03 g of pure material, and your minimum is 0.20 g. 0.03 ÷ 0.20 = 15%, so a 10% stock is fine (weigh 0.30 g), and so is a 1% stock (3.00 g). Choose by how much solvent you can accept.
A standard set
| Strength | Typically for |
|---|---|
| Neat | Main lines in larger batches |
| 10% | Most materials, and smelling |
| 1% | Strong materials and small lines |
| 0.1% | Very strong materials and traces |
Keep the strengths few, since every extra one is another chance of error. Sticking to factors of ten also makes the arithmetic easy, and it makes a wrong label more obvious.
What a stock brings with it
Each stock line carries solvent. A worked example follows, using invented lines for a 10 g target.
| Line | Pure needed (g) | Stock | Weigh (g) | Solvent carried (g) |
|---|---|---|---|---|
| A | 6.00 | Neat | 6.00 | 0.00 |
| B | 3.00 | Neat | 3.00 | 0.00 |
| C | 0.90 | Neat | 0.90 | 0.00 |
| D | 0.09 | 10% | 0.90 | 0.81 |
| E | 0.01 | 1% | 1.00 | 0.99 |
| Total | 10.00 | 11.80 | 1.80 |
The batch contains 10 g of pure material in 11.80 g. So this concentrate is 84.7% active, not 100%. If you then dilute it to a stated strength using a formula that assumed 100%, the result will be weak. Take the 1.80 g into account when you calculate the alcohol. The next lesson makes this rigorous.
Which solvent
Alcohol is common, since it evaporates and does not stay in the smell. Dipropylene glycol, triethyl citrate or isopropyl myristate stay behind, can suit materials that dissolve poorly in alcohol, and lose less to evaporation in a stock bottle. They become part of the formula, however, and may affect how the fragrance behaves, as our guide on fragrances diluted in carriers explains. Some materials react with a particular solvent, so check the supplier's notes. Pick one default, and make exceptions deliberately.
Keeping a shelf of stocks
- Label fully: material, strength, solvent, date made, source lot.
- Log them: stocks are materials in their own right. Each has a line in your stock log.
- Trace your batches: note which stock lot went into each batch.
- Remake small and often. Alcohol evaporates through poor caps, which silently strengthens the stock. If you plan to keep one a long time, write the gross weight on it when you make it, and check it later.
Practical exercise: Plan the stocks for a real formula
Pick a formula with at least eight lines, such as one of your accords or a formula from the library.
- Choose a batch weight, and calculate pure grams for each line.
- Find your practical minimum from your earlier test.
- Assign a stock strength for each line, and calculate the weight to weigh and the solvent carried.
- Total the pure material, the weight and the solvent, and calculate the active share of the concentrate.
- Add any stocks you must make to your shelf log.
You have done this well if no weighing is below your minimum, and pure material plus carried solvent equals total weight.
Common mistakes
- Too many strengths. A 3% next to a 5% will get confused one day.
- Ignoring carried solvent. It makes your finished perfume weaker than you intended.
- Trusting an old stock. Evaporation and aging change it, even with a neat label.
- Mixing up similar vials. Store different strengths separately, or color-code them.
Key terms
- Carried solvent
- The solvent brought into a formula by its diluted lines.
- Practical minimum
- The smallest amount you trust yourself to weigh on your scale, found by your own repeatability test.
Knowledge check
Written and reviewed by the RUŌOD Lab team. This is general education, not legal, regulatory, medical or safety advice. Example dilutions and exercises are for learning, are not validated products, and have not been safety-assessed. Completing a lesson confers no qualification. How we check these lessons.