At the core of any cleaning product is the surfactant. It can be any chemical, such as soap, which has the ability to lower the surface tension of water. Instead of forming round drops on the surface of materials, the surfactant will make water spread out and wet the material more efficiently so it can dissolve water soluble soils faster. Surfactants have schizophrenic molecules: one side of the molecule hates oil and loves water (hydrophilic), the other hates water and loves oil (lipophilic). This property allows surfactants to emulsify a solution, or to break down the water and oil molecules into small drops so they appear to be combined. When you add a drop of liquid soap to a pan filled with greasy water you can see how quickly the oil floating on the surface breaks into tiny droplets… so you can imagine the same grease spot on a dish or a favorite shirt. Since one side of the soap molecule is holding onto the oil and the other won’t let go of the water, all it takes is a little mechanical action such as scrubbing, the rotation of the washing machine drum, or the pressurized jets of water in the dishwasher, to dislodge the grease. All? Well, not quite.
Tap water is never pure H2O. Minerals such as calcium and magnesium are present to varying degrees. Water with a high mineral content is called “hard,” and for a surfactant to work properly water must be “softened.” The minerals must be rendered harmless either by sequestering them within the solution (by surrounding them) by precipitating them (transforming them into insoluble particles which drop out of the solution) or by ion exchange (swapping electrically charged ions to prevent the minerals from interfering with the surfactant). Traditional soap, defined as animal or vegetable fat saponified with sodium or potassium hydroxide, is particularly sensitive to hard water. This is why, despite the plethora of DIY recipes calling for soap, I will not use it in a machine. More on this later.
Detergents are much less sensitive to minerals than soap, but they still need soft water to work efficiently. The minerals tend to latch on to the surfactant molecules, preventing them from grabbing onto soils. There is a dizzying selection of surfactants made by the chemical giants of the industrialized world. Often these are skin irritants, but for most people only in much higher concentrations than those used in the end product.
“Builders” are chemicals added to enhance a surfactant’s cleaning power, primarily by softening the water. They include many types of phosphates, EDTA (a persistent organic pollutant because it does not biodegrade easily and it is widely used) but also less harmful chemicals like sodium carbonate (washing soda, which precipitates the minerals), borax and citric acid. Zeolite, a volcanic or man-made mineral with a honeycomb structure and a negative electrical charge, is used for ion exchange.
After the minerals have been dealt with and the soils have been lifted, the next step is to prevent everything from redepositing on clothes, dishes, or the machine. The white haze visible on clear glasses comes from the calcium settling back into place after the water has been rinsed off. Different chemicals are used to prevent redeposition, but the one I use is called methyl cellulose (or CMC for carboxy methyl cellulose) because it can also be used to make very pretty slime, marbleize paper and even delicious food.
Two more elements for proper cleaning don’t necessarily require a chemical solution: time and heat. A burnt pot of rice is impossible to clean, but if you soak it overnight the crust comes off effortlessly. Even with soap, bacon fat will stick to the pan till hot water is used to dissolve the grease. The problem is we often don’t have enough time to soak everything overnight, and we don’t want to use hot water either (to save energy or the color on delicate fabrics). The solution? More chemicals. Triethanolamine (aka TEA) is used as a low temperature activator and doubles as an anti soil redeposition agent but it is caustic and needs to be handled with great care.
Commercial cleaners then throw in a few extra features: enzymes break down certain molecules which helps remove stains, blue dye or optical brighteners are added to make white appear brighter (a bluish white seems brighter to our eyes than a yellowish white), and finally anti corrosion chemicals are added to protect not only the machines, but metal finishes on dishes and the paint on fine porcelain). Sodium metalsilicate is commonly used to protect metals from corrosion, but boric acid, sold in hardware stores as a cockroach killer, is a possible substitute. I prefer to use enzymes in pre-wash sprays, because they work much better when applied directly to stains, and when given time to work before being diluted and washed away. As for optical brighteners, putting a small amount of old fashioned bluing into the bleach compartment of the machine works just as well.
Scent does not effect cleanliness in any way, but it does influence the perception of cleanliness. I don’t think I’ve ever seen a TV ad for a detergent which did not include a shot of someone ecstatically sniffing laundry. Removing scent is a big advantage of making your own detergent, because it is often responsible for irritating sensitive skin. If you really can’t get used to neutral smelling laundry, you can mix 1/4 tsp essential oil with a drop of soap in a cup of water and spritz your clean, dry clothes with it.