Interest in the analysis of inks on paper has come primarily, although not exclusively, from forensic scientists. Two classes of problems are encountered: comparison of inks in different regions of a single document, to detect additions (such as adding a “ty” to your handwritten check for “nine” dollars) made with a visually similar but hopefully compositionally distinct ink; and verification of authenticity in documents (including stamps, stock certificates, currency, etc.) by the presence of specific tag elements in certain of the inks present.