‘Trace evidence’ studies the principles, techniques, and assessment of trace evidence examination (such as fibres, glass, or paint), and its importance in police investigations. Fibres are first examined crudely under a microscope, then matching fibres are examined further using microspectrophotometry. The composition of paint varies widely, but its examination is similar to that of fibres — the sample undergoes microscopy before being subjected to a chemical assay. Glass fragments do not stay on fabrics for very long and are ususally lost within a day. Again, glass is analysed using microscopy, with more advanced results available from interferometry.