Historic biocides have been found to fluoresce under ultra violet light at wavelength 366nm. We have investigated further this phenomenon to determine the variables associated with the fluorescence. The only metal responsible for the fluorescence was found to be mercury. Further tests and sensitive analysis using X-Ray spectrometry identified that over time the metal ion changed its valence state from Hg (II) to Hg (I). Mercuric (II) chloride does not fluoresce yet mercuric (I) chloride does and the reactions between components within the cellulose and the metal ions have been found to be responsible for the reduction of the mercury.