Crown ethers, cryptands, polyphenols, and several other reagents are known to have high specificity for various cationic species. These reagents have great potential for application in general conservation problems of selective cleaning, desalination, stain removal and reversal of treatments in conservation. They are remarkably more effective in metal ion complexation than the more common chelates (usually only EDTA is used for conservation applications) which are used generally with little regard for selectivity.
The advantages of a selective reagent are both its minimal effect on other species and its maximal cost-effectiveness. Most of the macrocyclic chelates are noutral specion that are lipophilic and solubilize metal ions (of the correct size) in non-aqueous media as well as water. Therefore, polar organic solvents may be used for water-sensitive treatments.
Research has been designed to assess the use of cationselective materials both in the laboratory and in situ. The potential of these compounds to expand the range and the safe execution of existing and new conservation treatments is excellent.