pH plays an important role in the performance of homebrew bubble juice. What we call "pH Adjusters and Water Conditioners" are ingredients that are used in bubble juice recipes to improve the performance -- generally through pH adjustment. This article provides information about additives that you can use and recommendations about how to use them. See the pH article for information about the importance of pH to bubble juice.
Baking powder, citric acid, baking soda + citric acid, distilled vinegar, cream of tartar and other ingredients are often used for making bubble juice because of the impact they have on pH.
The optimal pH range for a particular bubble juice may depend on both the surfactants and the other ingredients including the detergent. pH doesn't matter for most of the polymers and additives we use, but some of them (such as Japanese PVA-containing laundry starch) are sensitive to them. The exact reasons for this sensitivity is not currently known.
The effectiveness of detergents can be influenced by metallic ions and salts present in tap water and by calcium and some other minerals. In some (generally rare) cases, water conditioners that soften the water may be beneficial.
Baking powder or baking soda+citric acid are the favored tools for adjusting the pH as they do so gently -- making it hard to overdose a mix, and they do not require using a pH meter. Baking powder is more effective than baking soda + citric acid for reasons discussed below. Citric acid and tartaric acid (cream of tartar) are very effective BUT care must be taken because it is easy to overdo it and ruin your bubble juice if you are not careful A small amount of citric acid goes a long way.
Baking Powder Edit
Baking powder is perhaps the most effective and easiest to use pH adjuster. It is premixed to have the acidic and basic components in balance and is hard to overdose. It really should be added as the last ingredient when all you bubble juice's water is present. Baking powder has corn starch in it (often specially treated to be even more insoluble than it normally is) that does not dissolve in the water. Do not waste time trying to get it to fully-dissolve. It will not. The precipitate causes no problems. This is a key ingredient in Mike's Gooey Mix and the recipe provide with The Bubble Thing. Because it acidifies gently, careful measurement is not required. Recommended amount: about 1/2 teaspoon (approximately 2 grams) per liter of water seems to be the right amount for most tap water. Using more will generally be fine. The first use of baking powder as a bubble juice ingredient seems to be in David Stein's bubble juice recipe that is included with Bubble Thing. IMPORTANT NOTE: Not all baking powder is the same. We have found (Dec. 2013) that some brands of baking powder are less fast-acting than others and may need to sit for a considerable amount of time to take full effect. You may want to try a few different types in your mixes. Ideally, you want a baking powder that bubbles immediately when added to water. Weight/Volume Equivalence: 1/2 teaspoon (2.5 ml) of Rumford baking powder packed is about 2 grams. When the pH is lowered with baking powder, the pH of the juice seems to be quite stable. In a summer 2014 trial, a 20:1 water-detergent mix whose pH was lowered from its normal 9.0 to 6.8 with baking powder remained stable for at least 2 months.
Baking soda. Baking Soda + Citric Acid Edit
Some people use baking soda by itself as an additive to bubble juice, but it is much more common (and seemingly more effective) to use baking soda together with citric acid.
Baking Soda+Citric Acid. Baking soda plus citric acid is a popular combination for adjusting pH. There is no precipitate when it is used. So, some people favor baking soda+citric acid because it creates a nice clear juice. There will be a slight amount of cloudiness when Dawn and other Procter&Gamble dishwashing liquids are acidified. Baking soda+citric acid (plus water) also creates some sodium citrate which has been purported to have beneficial properties though Edward Spiegel performed experiments in Summer 2013 that seem to indicate that the benefit is almost solely the result of the pH adjustment since bubble juice treated with citric acid alone performed the same as juice made with baking soda+citric acid with the amounts adjusted so that the resulting juice had the same pH. Baking soda+citric acid is beneficial even when distilled water is used. This would not be the case if chelation or water softening (sodium citrate's main benefit) were factors. Weight/Volume Equivalence: approx 0.95 grams per packed 1/4 teaspoon. Recommended Amount: .5 to 2 grams per liter of water used with one-quarter to one-half that amount of citric acid. 1 gram baking soda per liter of water seems to work well for most tap water the with the appropriate amount citric acid.
IMPORTANT NOTE ABOUT BAKING SODA/CITRIC ACID (AUG 2014): In July 2014: we mentioned that reports from various people indicated that the relative amounts of baking soda/citric acid that people need to use seems to vary. Further investigation is showing that the pH of solutions acidified by using baking soda/citric acid (to create carbon dioxide) can vary substantially over time and is also temperature dependent. We are continuing investigations. Not only are the relative amounts important, so are the total amounts. Using pure CO2 to acidify mixes shows that an overstaturated solution will initially have a pH well below the desirable range but eventually stabilizes somewhere in the range of 7.8-8.2 for a 25:1 water:detergent dilution. With 2 grams baking soda and 1 gram citric acid per liter of water, the initial pH of a 25:1 dilution was about 6.8 rising to 8.2 over about 10 days (temperatures 70F-75F). When using 4 grams baking soda and 2 grams citric acid, the initial pH went as low as 6.4 but rose to 8.7 over the same 10 days. Because solutions are initially oversaturated with C02, the pH can be lower than desired -- but correcting the pH while still oversaturated can result in adding far too much baking soda -- up to 8 parts baking soda may be needed after the fact to bring the pH into the desired range--but once the excess CO2 outgasses, the result is an over-alkaline bubble juice. INVESTIGATIONS CONTINUE! For this reason, baking powder may be the preferred method for adjusting the pH in the absence of a pH meter. At least some baking powder's seem to create a more stable pH profile.
NOTE FOR EXPLORATION: Baking soda + cream of tartar (tartaric acid) is a combination that we have not yet explored but which is likely to be beneficial. Our guess is that a 1:1 ratio of baking soda and cream of tarter would be a good place to start.
Citric acid Edit
Growing consensus indicates that baking soda and citric acid when used together are very beneficial to giant soap bubble solutions. The exact proportions for maximum benefit have not been determined. See Baking Soda above. Also, see Recipes and search the blog section for entries related to baking soda/citric acid. Citric acid is available in many grocery stores (often sold as sour salt -- although sour salt is sometimes sodium citrate). It is sometimes available from bakeries or stores that sell baking ingredients. In some countries, it is sold for the purpose of de-scaling coffee machines. [EDITOR: make sure those entries are tagged appropriately and add a link to the appropriate tag].
Weight/Volume Equivalence.: approx. 1.1 grams per packed 1/4 teaspoon.
Recommended Amount: Precise amount will depend somewhat on your water's alkalinity. Note that pH and alkalinity are not the same; the amount of acid needed to achieve a particular pH will depend on the water's starting pH and alkalinity. The amounts mentioned below reflect Edward's findings with his tap water (whose pH tends to be in the range 9.0-9.02) unless otherwise mentioned. 6 ml. of a 5% Citric Acid solution added to 1050 grams of 20:1 tap water:Dawn Pro solution yields a friendly 7.6-7.7 for most water (equivalent to using 0.25 grams straight citric acid). This was tested with both tap water and distilled water. An additional 2 ml will bring the pH down to about 7.3. A total of 10 ml is likely to over-acidify the mix. It takes 3.5 ml citric acid solution to achieve a pH of 8.2. If using citric acid directly this is approximately 0.3 grams (< 1/16th tsp.) citric acid per 1050 grams of 20:1 bubble juice. 1/4 tsp (1.25ml) plus 1/8 tsp (.616ml) yields a pH of 7.5-7.6 when used with Edward's tap water.
Also see Baking Soda above.
DO NOT measure by volume when using straight citric acid.
Color change: when using citric acid to change the pH, the solution will became slightly milky/cloudy when the pH drops below about 7.8.
Cream of Tartar (Tartaric Acid) Edit
This is a weak acid often used in cooking. 1 gram (about 1/4 level packed teaspoon) will lower the pH of 1 liter of 20:1 tap water:Dawn Pro solution from about 9.0-9.2 to about 7.5-7.8. Juice made with cream of tartar compares favorably (based on preliminary tests in August 2014) juice conditioned with either citric acid or baking powder.
Other notes. 1/4 slightly heaping teaspoon of cream of tartar added to 1 liter of a 25:1 tap water:Dawn Pro lowered the pH from 9.1 to 7.4.
Other Water conditioners Edit
Vinegar. Distilled vinegar can be used to lower pH but trials in July/August 2014 seem to indicate that juice made with vinegar does not seem to work as well as juice conditioned with citric acid, cream of tartar (tartaric acid) or baking powder.
Color Change and Stability Edit
The importance of when you add baking powder or baking soda+citric acid Edit
Getting any benefit from baking powder or baking soda+citric acid depends on when you add these ingredients. Most of the benefit is due to the pH shift caused by the carbon dioxide they give off when they react with water. Some of the carbon dioxide dissolves in the water and forms carbonic acid. Because carbon dioxide is not very soluble in water, only a small amount of carbonic acid is created. The result is very gentle acidification (which counteracts the detergent's alkalinity).
If all of the water is not present when the reaction occurs, the primary benefit of the reaction is missed. While the benefit is subtle in some cases, it is also quite distinct especially once one has experience.
If you add these ingredients to a concentrate and then dilute the concentrate, you do not get the pH-adjusting benefit which is their primary benefit. The ingredients must be added when all of the water is present. For this reason, it can be useful to add the baking soda when making the concentrate and then add the citric acid to the water used for the dilution. Baking powder has the advantage of not requiring careful measurement. So, it is often convenient to simply use baking powder after dilution.
Note that if you use baking soda+citric acid for fizz mixing your polymers, you need to add some more once your mix is at full dilution.
This is easy to test with a pH meter.
Experiments in 2013 demonstrated that contrary to popular belief, the pH change induced by the dissolved carbon dioxide is permanent and does not quickly dissipate.
Historical Note and Analysis Edit
While a few people were using these additives prior to 2011, they were not in wide use. They started being widely used by SBF members in Feb. 2011 following and many claim that it has significantly improved their solutions (with no notable dissent).
While the exact mechanism is not entirely certain, it seems increasingly certain (per Edward Spiegel's 2013 explorations) that the benefit is due to the pH sensitivity of the detergents used for bubble juice. There may be additional benefits related to chelation though there seems little evidence for this -- since the same benefit is found even with distilled water where chelation would be irrelevant.
Others have suggested that it is due to the influence of sodium citrate on the detergent's viscosity. Investigations of Alan McKay's claims [editor: add citation] about the benefits of baking soda + citric acid as beneficial to bubble solutions have led quite a few people (with no notable dissent) to feel that the combination is of great benefit to giant bubble solutions. The optimal concentrations of each has not been determined and seems likely to be somewhat related to the water that is used. For some people (possibly people with acidic tap water), the baking soda must be added early in the mixing process (before polymers and soap) and citric acid must be added only after the solution is stable and hydrated. Others find that they can add both together with the polymers. .8 to 2 grams of baking soda per liter of bubble juice plus about 1/2 that amount of citric acid per liter of bubble juice seems to be a beneficial range for most people that have reported on their use of these additives. Some people use a ratio of 2 to 1 (baking soda to citric acid) while other use 1.3 to 1 (based on the theory that the benefit is solely from the creation of sodium citrate that occurs when baking soda and citric acid are mixed with water). Others seem to find that some additional amount of baking soda is helpful although that may be particular to the pH of their water. There have not been any detailed experiments documented, yet.