Whether it is lemon juice from your fridge, detergent bleach from your laundry cupboard or chemical solvent from your local hardware store, all stain removers operate on one of four basic principles:
- Dissolve the Stain Using a Solvent
The most common and universal solvent is water and many stains, especially if caught fresh, can be lifted off simply by flushing with or soaking in water (or in the case of carpets and non-washables, dampening and then blotting with paper towels). However, some stains contain substances that do not dissolve in water, for example grease stains like butter. These will require organic solvents, such as alcohol. In general, “like dissolves like” – thus, a stain made from hydrocarbons (e.g. motor oil) can be removed by a hydrocarbon solvent (eg. gasoline). Limonene is an organic molecule that is found in citrus fruits (e.g. oranges, lemons) which dissolves a lot of grease stains and certain kinds of fruit stains – it can even work on inks, graffiti, candle wax and gum. So lemon juice is a good stain remover to try in many situations.
- Dissolve the Stain Using a “Surfactant”
An alternative to using an organic solvent is to lift the stain off with the help of a “surfactant”, such as soap or detergent – these surround the stain molecules and make it easier for water to detach them from the fabric and carry them away in the rinse. Thus, in the grease stain example above, instead of using alcohol which could damage the fabric, you could apply some detergent to the grease stain first. Note, however, that stains which have dried may not respond to soap and detergent with water and may need to be treated with the appropriate solvent. Synthetic surfactants, such as sulfonates, are used more often than soap nowadays as they do not react with hard water to form calcium deposits (“soap scum”). However, they are far more toxic to the environment and are not biodegradable.
- Attack and Destroy the Stain Particles
If the stain cannot be easily dissolved, then it may need to be “cut up” through the process of oxidation. Oxidising agents, such as chlorine bleach, peroxides and borax, break up the links holding the stain molecules together, thus enabling the solvent to flush them away more easily. Biological and enzyme detergents often provide this action on stains, especially food-related stains – they work by releasing enzymes that act as a catalyst to speed up the chemical reactions which digest the proteins and fats in the stains. However, biological enzyme products must never be used on wools and silks.
- “Hide” the Stain
As a last resort, it is possible to make a stain “invisible” if you cannot remove it from the fabric. Thus, although the stain molecules remain embedded in the fabric, they are rendered colourless so that you can no longer see them. This is how bleach works: by disrupting the bonds between the chromophore molecules (which absorb light at specific wavelengths and so “produce” colour), the optical properties of the molecule are changed and thus they become “colourless” to our eyes and thus, we say that the stain has been removed. In actual fact, it is still there but we just can’t see it anymore. Unfortunately, bleach does not distinguish therefore it will also remove colour from the fabric that the stain is embedded in – thus it can really only be used for white fabrics. However, a very mild solution of bleach (oxygen bleach rather than chlorine bleach) can sometimes be used with care on coloured fabrics.
Lastly, before tackling any stain with any type of stain remover, it is best to try and remove as much excess soiling substance as possible, whether by brushing or blotting with paper towels or even (especially in the case of grease stains, which can smear badly) using some corn starch, salt or talcum powder to absorb as much from the surface as possible. In some cases, if the stain is fresh, this absorbent treatment may be all that’s needed to lift the stain – for example, salt on red wine stains.