How to calculate how much perfume is left in opaque bottles
A perfume bottle in a tinted shade of purple or black looks classy and beautiful, but it can make it difficult to gauge how much perfume is left inside. Having an idea of how much perfume is left makes it easier to know when to restock. Also, if you plan to trade or sell a perfume, you need to know how much fragrance is left in the bottle. Here are several options for measuring the amount of perfume left in the bottle:
Bright light
One of the most effective methods of measuring perfume content is to shine a bright light through the bottle. Ideally, the perfume bottle should be kept and stored away from direct sunlight. But there is an exception to this rule and that includes trying to see how much liquid is left at the bottom.
Hold the perfume bottle in front of a window that gets sunlight during the day. Even opaque bottles can give some kind of clue about the volume of perfume that is left. It is often possible to see a line to indicate the gap and where the liquid begins.
If you do not have enough natural sunlight to perform this test, it is possible to use a very bright light bulb (60 or 100 W). This again should allow you to take a look at the line to show how much perfume is left at the bottom of the bottle.
sink in the water
Another option is to submerge the perfume bottle in water. Although this is not a practical method for older bottles with a paper label, as it can damage the label when it begins to dry. In this method, it is a simple process relying on physics. By immersing the perfume bottle in a pitcher or vase of suitable size it is possible to produce a substitution of the volume of the water for the volume of the bottle. This is accomplished by placing the perfume bottle in the water and letting it float to the surface. It will float to a height where it is still full. This can give a very good idea of how much perfume is left in the bottle.
However, by following the light or water method, it should be possible to get a more accurate signal of the amount of perfume left in opaque or dark bottles. Shaking the bottle is another option to see if any liquid remains, but this is not a very accurate method.