Stain Removal #1: General Principles

The questions I get most commonly asked revolve around stain removal.  And it’s not just me – people like Shannon Lush have made a full-time career out of it.

For me, these questions are simply chemical questions.  That is, since everything we see and touch is a chemical, any question about stain removal is simply a question about how to remove one chemical from another.  Or, to be more exact, it is about how to make one chemical look as though it has been removed from another.

In general terms there are three approaches we may take:

1.  Separate the stain from the substrate.  This is the gentlest and by far the most common approach.  This is the role adopted by surfactants (detergents).  They separate the stain from the substrate (e.g. clothes or crockery) and allow it to be dissolved and carry it away.  If this approach doesn’t work, it may be for reasons such as that the stain has formed a bond of some sort with the substrate that is not easily broken.

2.  Destroy the stain either partly or wholly, without destroying the substrate.  This is particularly effective if the stain is a food dye or other natural or synthetic dye of some sort. These dyes tend to be large complex organic molecules that are very fragile – that is, they are easily susceptible to chemical attack.  And the most common form of chemical attack is oxidation with one of the many different types of bleach that are available.  All we have to do is destroy or modify one part of the molecule, and this often disrupts its electronic structure to the extent that the colour disappears.

This is also the domain of enzymes, highly specialised chemicals that specifically attack certain classes of stain.

The danger with this approach, of course, is that wherever you are oxidising a stain, you are potentially oxidising the garment as well.

3.  Remove the stain by removing part of the substrate that it is attached to.  This of course is not just a chemical approach – it is a physical approach.  If for example you had bore stains on something and you were unable to remove them chemically then you may remove them by scrubbing off the upper layer of paint that they are attached to.  Another example of this may be the removal of stains on cement by the use of hydrochloric acid to dissolve the upper layer of cement.

This approach does not, of course, apply to garments.

In subsequent posts I will dig into each of these approaches in detail, and describe the various ways in which stains maybe removed, disabled, or destroyed.