Five years ago as leather became more popular, I decided to train and research in it's cleaning and I have now cleaned many leather sofas.
To clean properly first requires an accurate assesssment of the type of leather finish which we are dealing with.
There are many different leather finishes by far the most popular of which is pigmented or painted leather.
These are typically cream or off white , but can be black , green , blue, pink etc.To clean these effectively requires good quality chemicals , specialist stain removers and hard work ! Excellent results can be achieved and minor repairs of scratches can be carried out.
Stain removal is more complex and depends on whether the stain is on the pigment, or has been absorbed into the leather.
If it's on the pigment, then there is a good chance of removing stains although ink or dye transfer from say, a cushion or 'throw' can be very difficult.
If the stain is in the leather then it is almost certainly going to be impossible to remove, this is where leather protectors become important. A good quality leather protector such as the one used by us will form a barrier to stains allowing them to be much more easily removed. It will also prevent body oils sinking into the leather and undermining the pigment.
Other types of leather are much more difficult to clean.
Aniline dyed leather is absorbent and stains and dirt will sink in and become permanent making protection even more important, as it is far better to prevent rather than attempt to cure .
Suede and Nubuck are very absorbent and virtually uncleanable , again protection is the key.
www.leatherclean.co.uk has some pictures.
If you want to DIY clean your leather sofa then products used by professionals but available to you also can be found at Leather Cleaning Products .These products can also be used on handbags, car ineteriors including car seats and leather jackets.