About this article. This article is not a recipe (those are found elsewhere on the Wiki). This article is intended to as an introduction to concepts critical for understanding how bubble juice works. If you are an experimentalist, this information is critical and will save you a lot of frustration. If you are just looking for a bubble juice recipe, visit the Recipes page. Come back here to learn the basics when you're ready to start experimenting seriously.
If you are new to bubbling, you may want to check out the Getting Started page.
Soap bubbles and the "juice" used to make them are full of surprises. The physics and chemistry of soap bubbles is quite complex and many important truths are counter-intuitive. There are a lot of myths (aka conventional wisdom) that seem intuitive -- yet are flat-out wrong. We hope this article will lead to a better understanding of bubbles and make your explorations more fruitful. If you find errors or have results that contradict our conclusions, let us know. Our goal is to be fact rather than myth based.
This article outlines the basics of bubble juice as we understand them and is based on countless hours of experimentation here at the Wiki and around the world. Over the years, we have revised our view quite a bit as experimental evidence has sometimes demonstrated that widely held beliefs on this subject have often been mistaken -- or based on incomplete information.
Bubble Juice Composition Basics Edit
THE BIG THREE
- Water (required)
- Surfactant (required)
- Polymer/goo (nearly essential)
- ph-Adjuster (advisable)
- Humectants (only sometimes useful)
- Chelating Agents and Water Conditioners (only in special circumstances)
Generally-speaking, effective bubble juice requires three classes of ingredients and often benefits from some additional types of ingredients. The critical ingredients are: water, surfactant, and a polymer. It is possible to make bubbles with just water and surfactant, but such solutions are difficult to use. Polymers make bubbles easy to close and often provide additional beneficial properties.
Water and Surfactant. You cannot have soap bubbles without surfactant (soap or detergent) and water. The choice of surfactant is critical. If you are making your own bubble juice, you will usually be using a dishwashing liquid. See the Detergent article for information about recommended detergents. Generally-speaking, you can use whatever water is most readily available. Contrary to popular belief, distilled or other purified water is not preferable to tap water. There are cases where tap water can't be used but those are relatively rare. Read all about water here.
Polymers and goo-makers. It is not easy to make bubbles with a mix that is only surfactant and water. It can be done, but it can be tricky. This is where polymers (which I sometimes call "goo-makers") come in. They make it much easier to blow streams of bubbles and close bubbles. While you might be able to blow bubbles without them, they make it so much easier that I consider them (with rare exception) an essential ingredient. Polymers can be natural products like guar gum (which is a simply a powder made by grinding up a particular kind of dried bean) or synthetic products such as Polyethylene Oxide (PEO). Interestingly, the most common polymers do not change film thickness (though they influence the viscosity) even though they can significantly boost the number of bubbles per dip. By contrast, when bubbles-per-dip is boosted by increasing the surfactant amount, the film thickness is generally reduced considerably.
What is a polymer? A polymer is nothing more than a large molecule made up of chains of similar subunits called monomers.
What do they do? The precise role that polymers play is a mystery. Despite widespread belief, numerous experiments have shown that polymer benefit is not directly related to viscosity. Some polymers are highly effective without changing the viscosity significantly while others are only effective at levels that result in very viscous juice. As far as we know, no one yet understands the polymer role well enough to predict its benefits by looking at polymer characteristics. Trial-and-error is currently used to determine which polymers work well and what properties they bring with them.
Useful polymers add stretchiness or suppleness (which some people -- mistakenly in our opinion -- call elasticity) that allows the film to stretch without breaking. The most useful polymers also provide a property that is often called "self-healing": the ability for a bubble to re-close (heal) when tiny holes appear on the bubble surface. Self-healing and suppleness make it easy to blow bubbles in bubbles. Supple bubbles will deform when attacked by external forces rather than pop.
Much more information can be found in the main Polymers article.
Where is the glycerine? You might be surprised that glycerine is not listed as a primary ingredient. While glycerine is often listed as the critical ingredient in many recipes that you find in print and on the web, much experimentation has shown that its reputation as a critical ingredient is undeserved (though there are cases where it is a key ingredient). Its original reputation is in part due to early literature (from the 1920s and before) on soap films when the surfactant systems used were quite different from what we generally use. You can make world-class long-lasting bubbles without it. Find out more in Glycerine_Basics_and_FAQ
Other Optional Ingredients Edit
pH Adjusters. These are useful because the effectiveness of most surfactants changes with pH. Adjusting the pH to the correct level has an impact on many bubble qualities: soap film wall thickness, longevity, "strength", and friendliness. In many situations, pH-adjusted juice just seems to work better in ways that people might not be able to put a finger on. Bubbles seem easier to close and less prone to premature breakage. pH also often has a marked impact on the soap film thickness or the amount of surfactant needed to achieve a particular soap film thickness.
The ideal pH for a bubble juice depends on its ingredients. Some detergents are more influenced by pH than others, and pH has a bigger impact in some dilution ranges than others. The most common pH adjusters are baking powder (which is almost impossible to misuse), citric acid, tartaric acid (cream or tartar) and sometimes baking soda plus citric or tartaric acid. Beer, vinegar, and carbonated water are used by some bubblers as well.
Humectants. These are ingredients such as glycerine and propylene glycol that technically-speaking slow down evaporation due to their affinity with water. However, in practice, humectants often have little or no impact on actual bubble longevity. Most recipes that you find that call for glycerine do not actually use enough glycerine to measurably impact bubbles. There are certain situations in which humectants are helpful. See Glycerine and Glycerine_Basics_and_FAQ
Chelating agents And Water Softeners. In some conditions, water is so mineral-rich that a water conditioner that provides chelation or water softening is needed. Such conditions are quite rare when using commercial dishwashing liquid as your base.
Freeze-preventers. If you are bubbling in freezing and near-freezing temperatures, additives may be useful to prevent freezing. Calcium chloride and propylene glycol are sometimes used to this end. See Cold Weather Bubbling
Dilution, Bubble Thickness and Color Edit
A bubble film's thickness is almost mostly determined by the surfactant concentration or dilution (and not by its viscosity); pH can influence it also. Viscosity does not influence it. The skin's thickness determines the colors. The film thickness also influences other properties like "strength" and longevity. The relationship between bubble wall thickness and soap concentration is the opposite of what most people assume. Dilute solutions result in thicker bubble walls than solutions that are more concentrated.
Learn about the connection between color and soap film thickness in the article Color and Film Thickness.
Dilution can have a huge impact on bubble longevity, color, the number of bubbles per dip, and maximum bubble size. In some cases, you need to determine which quality is most important and adjust the dilution accordingly as there are sometimes trade-offs between properties.
Reducing the amount of surfactant (usually detergent) in a solution tends to result in a thicker soap film (which tends to boost longevity, especially in less than ideal humidity) and may reduce the number of bubbles per dip (though you can usually compensate for that by increasing the amount of polymer in your mix or using a different polymer). Increasing the amount of surfactant (detergent), usually results in a thinner soap film (which can reduce longevity in non-ideal conditions and may make bubbles more fragile, though fragility is a complex phenomenon). Increasing the amount of detergent sometimes increases the number of bubbles per dip (usually at the expense of longevity).
Since color is strictly a function of film thickness, you can tune a bubble juice's color profile by tuning the dilution. And you can use color to determine the thickness of the bubbles. Seeing a bubble's colors, of course, requires reasonable lighting conditions and usually a dark background. A chart of bubble colors and their associated thicknesses can be found in the article Color and Film Thickness.
Comparison of thick and thin skinned bubbles. The videos below were created in the same conditions with bubble juices that create very different initial film thicknesses. The video on the left shows a thick-filmed bubble. Notice that the colors are initially dominated by the pinks and greens associated with films 700 nanometers and thicker while the thin-skinned bubble starts off with some areas as thin as 100 nanometers (as evidenced by white spots). Another interesting characteristic of thin-skinned bubbles is the tendency for the initial color swirls to continue longer than they do in thick-skinned bubbles. Note: I am blowing on the bubbles which shortens the lifespan due to evaporation and stress. Under less stress, the difference in lifetimes would be even larger.
Critical dilution. In some dilution ranges (usually low dilutions) changes in detergent concentration have less of an impact on the film thickness than on others. In this case, the films are usually pretty thin to start with.
Viscosity is a widely misunderstood aspect of bubble juice. Because some brands of commercial bubble juice and many commercial dishwashing liquids are often very viscous (thick), people often associate viscosity with effectiveness. People frequently assume that a "thicker" (meaning more viscous) solution will lead to thicker, stronger soap films. But, this is not necessarily the case. Viscosity is not directly connected to the soap film thickness or any important bubble quality. The relationship between viscosity and bubble qualities is a complex one and is deeply tied to the particular polymer that is used.
Some polymers (such as PEO) have a profound effect while barely changing the bubble juice viscosity while other polymers may increase viscosity significantly and only marginally improve the mixture.
A common mistake by bubble brewers is to make bubble juice more viscous when they are unhappy with longevity or durability of their bubbles. But, changing viscosity is rarely the solution to the problem.
While some bubbles pop into a fine mist or droplets, some bubble juices create bubbles that seem to break up into tissue-like fragments that we call "ghosts". These tissue-like fragments are really bits of foam created as parts of the bubble pull together during the bubble burst. Ghosting is related to the surfactant being used and is not an indication of a problem. Depending on the detergent, ghosting is sometimes an indication of optimal performance rather than a problem.
Reach all about them in the Ghosts article.
Myth: "Distilled water is best." Tap water is generally preferable. With the exception of extremely hard or mineral-rich water, tap water usually performs as well as or better than distilled water in a mix that includes appropriate pH adjustment. See Water.
Myth: "Glycerine is an essential ingredient." Testing has proven this simply isn't true with the dish detergents now available. See Glycerine_Basics_and_FAQ.
Myth: "Thick solutions make strong or thick bubbles." The thickness (viscosity) of a solution has nothing to do with how strong, thick or colorful bubbles are. Because commercial bubble juice and dishwashing liquids are often quite viscous, people often associate viscosity with effectiveness. Some of the best bubble juices have a viscosity closer to water's than to the viscous solutions people often associate with soap bubbles. See Viscosity and FAQ:_Thick_Solutions.
Tweaking Recipes Edit
We recommend that you start with a simple recipe that is reported to be reliable. We offer some recommendations in the Getting Started section of the Recipes page. When you get started, we recommend slavishly following the recipe and trying out any options (such as exploring dilution or polymer amount) suggested by the author.
If you are interested in tweaking a recipe to see what it does, here are a few pieces of advice and a few things to keep in mind:
Playing with the dilution can have a big impact. We generally think that it is beneficial to become familiar with your favorite detergent at a few different dilutions. Using less detergent creates thicker films. Using more detergent makes them thinner. More detergent sometimes increases the bubbles per dip (but often at the expense of longevity and/or aesthetics -- you may get a lot of colorless bubbles at the end of a dip).
Whether the dilution has an impact on the bubbles-per-dip or maximum bubble size will depend on both environmental conditions and the equipment being used. If your bubble device (like a tri-string wand or bubble hoop) has a high juice-holding capacity, changes in dilution may not have a huge impact (except at extreme dilutions) on the maximum bubble size -- especially in less than ideal humidity. If the humidity is high, the differences in longevity due to film thickness may be less obvious than in drier conditions.
Playing with the polymer amount also has a big impact. The exact nature of the impact is highly dependent on the particular polymer. Increasing the amount of polymer often increases the bubbles-per-dip. Usually polymer amount is a better way to tweak bubbles-per-dip than detergent amount since polymer amount generally does not impact film thickness. Increasing the polymer amount may (though it depends on the polymer) increase the degree of self-healing. Self-healing influences the ability to make bubbles-in-bubbles and also the tendency of a bubble to split into smaller bubbles when acted upon by the wind. Too little polymer often results in difficulties closing bubbles or being able to blow bubbles-in-bubbles. Too much of some polymers can be problematic. For instance, too much PEO results in very stringy juice and fragile films.
Sometimes you may want to tweak a recipe for particular equipment or conditions. If you are having problems with blowouts when it is windy, it might be beneficial to reduce the film thickness by increasing the detergent amount, since releasing the same amount of juice is essentially releasing more "bubble feet". However, the thinner film may end up being more fragile. When it is dry, you might want to use less detergent in order to create a thicker film since they take longer to thin and evaporate.
This article is an attempt to provide some important basics that can help people explore bubble juice mixology. Most of the information here is discussed in greater detail elsewhere on the Wiki. My hope is that this article will provide a quick orientation.
People often tell me that they have tried this or that bubble juice recipe and want to know how to make the bubbles work better. Often, they suggest things that they think that they should try. I asked most of those questions myself when I got started. When I got started, there were lots of recipes to be found and lots of discussion of bubble juice issues on SBF, the Soap Bubble Fanciers Yahoo Group, but there was not much in the way of specific information that could be used to help decide which avenues of exploration would be fruitful.
See Also Edit
The following articles are critical to gaining a deeper understanding of bubbles and bubble juice:
- Site Index - the site index lists many helpful articles that you might otherwise miss!
- DIY Surfactant Base
Don't just take our word for any of this. Explore and experiment. Here is our claim: the information here is based on a lot of experimentation and review of experiments by reliable sources. We have tried to set up experiments to determine the truth and accuracy of what we claim to be true. If you have an experience that contradicts anything you have read here, PLEASE let us know -- we strive to update the information to reflect reality rather than our prejudices.