* Volume refers to the concentration of hydrogen peroxide. A 40 volume developer contains a higher concentration of hydrogen peroxide than a 20 volume developer.
* Dilution is not a simple ratio. You can't just add water to a 40 volume developer to get 20 volume. The chemical reaction involved in hair bleaching is complex, and simply diluting the peroxide won't result in the desired strength.
It's crucial to understand that diluting hydrogen peroxide is not safe to do without proper knowledge and equipment. You risk creating an unstable solution that could be dangerous to use.
If you need a 20 volume developer, it's best to purchase it pre-mixed from a reputable supplier.
