Diamond, alumina, or silica polishing media may be used. Typically, a brief, final polish with 1 m m diamond yields an adequate polish without compromising flatness. Do not use a polishing medium which will contaminate the sample with the elements to be studied. Sample Coating For almost all work in the geological sciences, samples must have an electrically conductive coating which makes contact with the tantalum cover plate on the sample holder. Either gold or carbon coats are used.
Gold is preferred, being more conductive and more easily sputtered than carbon.
Clearly, carbon should be avoided if C-isotopes are to be measured.