The advanced materials and deposition processes including recent developments in ultra hard materials like BAM (AlMgB compound)are fully covered in a recent book[R. Chattopadhyay:Green Tribology,Green Surface Engineering and Global Warming,ASM International,USA,2014] In 1995, surface engineering was a £10 billion market in the United Kingdom.
Coatings, to make surface life robust from wear and corrosion, was approximately half the market.
In recent years, there has been a paradigm shift in surface engineering from age-old electroplating to processes such as vapor phase deposition, diffusion, thermal spray & welding using heat sources, such as, laser,plasma,solar beam.microwave;friction.pulsed combustion.
[Ref:R.Chattopadhyay:Advanced Thermally Assisted Surface Engineering Processes,Springer, New York, USA,2004] It is estimated that loss due to wear and corrosion in the US is approximately $500 billion.
The purpose of surface cleaning is to reduce the potential for damage to paper artifacts by removing foreign material which can be abrasive, acidic, hygroscopic, or degradative.
The decision to remove surface dirt is also for aesthetic reasons when it interferes with the visibility of the imagery or information.
A decision must be made balancing the probable care of each object against the possible problems related to surface cleaning.