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Longevity Test

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(Work-in-progress) This page will be devoted to an article about Longevity Test setups. For the time-being, see also the Longevity Test category and Edward's Test Matrix page.

This is a simple, primitive apparatus that has turned out to be extremely useful in evaluating both detergents and bubble juice. It consists of a plastic bottle whose bottom has been removed. The bottle's mouth is dipped in the solution to test, turned right-side up, and lowered into water. 

This allows one to compare bubble lifetimes (if adequate repetitions are performed) in a meaningful way.

It was inspired by an apparatus [1] [2] that was a matrix of test tubes open on the bottom and top. The test tube matrix was inverted, and the rims dipped in a tray of soap solution. The matrix was turned right-side up and lowered into a tray of water.

Edward's Longevity test apparatusEdit

Equipment needed:Edit

  • Plastic bottle with the bottom cut off. A one pint (half liter) or one quart (one liter) water bottle works fine. Pictured is a one liter gatorade bottle. This is the bubble maker.
  • Dipping container. The container needs to be bigger around than the bubble maker (your plastic bottle). Pictured is a one liter glass measuring cup.
  • Bubble juice.
  • A cup or saucer to hold the bubble juice


Longevity 20130802 5163 container
Bubble maker. Plastic bottle with bottom cut off. For the best results, cut out the bottom by going around the rim rather than by cross-cutting at the bottom. This will help the bottle stand level
Longevity 20130802 5164 vessel
A container (here a 1 liter glass measuring cup) into which the plastic bottle will be lowered. You should fill this to a pre-determined level that you keep the same in future tests to maximize meaingfulness. The water level will determine the bubble size.
Longevity 20130802 5156 dipping
Dip the top of the plastic bottle into your bubble juice.
Longevity 20130802 5158 lowering
Lower the plastic bottle into the dipping container until it rests on the bottom.
20130802 5175CROP8to1

Dawn Pro at 8:1 (water:detergent) with Edward's longevity test setup

Time the bubble's life and observe the colors. Make note of whether the colors change. Some solutions will have a sudden color drain.
20130802 5138 Longevity Test Demo00:36

20130802 5138 Longevity Test Demo

Watch a demonstration
Another demonstration of the technique
Longevity Test Demo00:58

Longevity Test Demo

A demonstration of how this might be used to compare different solutions.
2013 09 200 all compared labeled00:36

2013 09 200 all compared labeled


For the results to be meaningful across sessions, you must record the temperature and humidity.

Ideally, at least 10 repetitions should be performed for each solution in a session.

A control solution that is used in all sessions (such as a simple 10:1 water:detergent mix) is very helpful. It can help calibrate between sessions -- and give you an idea of whether there may be special environmental circumstances in play for any given session.

Care must be taken after each repetition to shake excess water from the bottle -- otherwise your target solution will become more dilute over time.

Care must be taken to take the same amount of time and use the same motion when dipping and lowering the container.

Care must be taken to start the timer at the same point. For instance, start the timer as soon as the container has been completely lowered.

For data to be compared across sessions, you must use a standard water level in the outer container. This creates a standard volume.

In theory, if you could measure the diameter of the bubbles accurately -- you could compare the surface tension of solutions by comparing the volumes of the created bubbles as long as the water level is carefully controlled.

Some thought can be given to the water level to determine what size bubble is most useful for evaluation. It might be possible to compare the 'stretch' that a solution has by measuring the maximum bubble size that can be made with a given apparatus.

Applications Edit

This test has a few useful applications:

  • comparing longevity of bubbles made with different solutions
  • evaluating detergents for optimal dilution range

Evaluating detergents for optimal dilution rangeEdit


Variants and Improvements Edit

The test is not perfect and a reasonable number of repetitions must be performed as there is a fair amount of statistical noise due to both environmental variables (such as floating particles whose distribution may change over time) and performance issues (such as the time taken to dip and place the bottle). Adequate repetitions within a session and repetitions of the session do a very good job of evening out discrepancies.

Due to environmental variation (air quality, humidity, and temperature variations) care must be taken when evaluating the results of different sessions. For this reason, it is useful to use a control solution in all sessions to give a sense of how the session's results compare to others.


Performing multiple repetitions is cumbersome, especially for solutions with good longevity. An apparatus that allowed multiple bubbles to be created simultaneously would be very helpful.

It has been suggested that the test could be made more meaningful by performing the test in an enclosure or by lowering an enclosure when lowering the bubble. There are some pros and cons to such a method. One issue is that the longevity increase can be rather dramatic, making multiple repetitions impractical. The longevity of  even mediocre solutions can be extended up to a minute, and only moderately long-lived solutions may create bubbles  that last for more than five minutes. Some amount of exposure to the environment does not seem to significantly detract from the meaningfulness of the results and may have some benefit. Exposure to the environment seems to provide some useful test of the the solution's toughness as opposed to a simple gauge of the rate of evaporation.

A method for restoring the film without the need of inversion would be helpful since inverting the container can result in water dripping into the soap solution when dipping if the bottle is not adequately shaken dry.

Thoughts and Discussion Edit

Things to add to the pageEdit

Sample worksheet showing data to be recorded.

Video showing color drain.

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