In short
When you change a line's dilution, something else must give. You can hold the line's weight (and lose active), hold its active (and the formula's total grows), or hold both active and total by removing an equal weight of solvent from elsewhere. These are different decisions, and each gives a different formula.
What you will learn
- Compare three ways of changing a line's dilution
- Predict how each changes the total and other lines
- Decide whether a retained solvent matters to the smell
Before this lesson: Active Material: The Number Behind Every Formula
The three moves
Take a formula totalling 10 g, with a separate solvent line. One line, B, is 2.00 g at 10%, which is 0.20 g of active, and you now only have B at 1%.
| Method | B weighs | B's active | Formula total | Other lines |
|---|---|---|---|---|
| Hold weight | 2.00 g | 0.02 g | 10.00 g | Unchanged, but B is now a tenth as strong |
| Hold active | 20.00 g | 0.20 g | 28.00 g | Unchanged in weight, smaller in share |
| Hold active and total | 20.00 g | 0.20 g | 10.00 g, if 18 g of solvent can be removed | The solvent line must fall by 18 g |
The third row exposes a limit: in a 10 g formula you probably have nowhere near 18 g of solvent to remove. In that case, it cannot hold both, and you must either accept a growing total or work with a stronger dilution. The reference on changing dilution in a formula works through further cases. These three methods are also what the RUŌOD Lab app offers when you switch a line's dilution.
Choosing
- Hold the weight only if you are deliberately reducing the material.
- Hold the active when the fragrance must stay the same and you can accept that the concentrate becomes more dilute. Finish the perfume by active rather than by concentrate weight, or it will be weak.
- Hold active and total when a batch has a fixed size and a solvent line is available.
When solvent is more than arithmetic
Alcohol evaporates quickly and leaves the materials on the substrate. Solvents that stay behind can behave differently:
| Solvent | Notes for a formula |
|---|---|
| Dipropylene glycol | Nearly odorless, slow to evaporate. May affect release. |
| Benzyl benzoate | Faint balsamic odor; also a fragrance ingredient; a listed allergen in some markets. |
| Triethyl citrate | Low odor, often chosen by those avoiding other carriers. |
A 5% line of a heavy solvent may have little effect, but a third of the concentrate might. If you change solvents, test it. Also check the regulatory side: a solvent is an ingredient too, so it has to be declared and checked like any other. The guide on fragrance oil carriers shows how this catches people out when they buy fragrance oils with hidden carriers.
Compare before you commit
Arithmetic tells you that two versions should contain the same active. It cannot tell you that they smell the same. Make both, and compare blind. A difference may be real, or it may come from aging, a different lot or weighing error. That gives you one more reason to record which lots and stocks you used.
Practical exercise: Switch one dilution three ways
Use this formula: A 5.00 g neat, B 2.00 g at 10%, DPG 3.00 g. You only have B at 25% now.
- Calculate B's active: 0.20 g. Find the weight of B at 25% to hold that active. 0.80 g.
- Hold weight: B stays at 2.00 g at 25%. What is B's active now? 0.50 g, or 2.5 times more.
- Hold active: B falls to 0.80 g. What is the new total? 8.80 g.
- Hold active and total: how much DPG must you add? 1.20 g, so DPG becomes 4.20 g and the total stays 10.00 g.
- Write which you would choose in a fixed 10 g batch, and why.
You have done this well if your totals tie out and your reason refers to what you need to hold constant.
Common mistakes
- Changing a stock and keeping the weight without noticing. This is the most common way a formula silently changes.
- Treating all solvents as equal. Some stay behind and some have an odor.
- Forgetting that a new solvent needs checking. It has its own documents and rules.
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.