This paper deals with the non-destructive documentation of the copy letters of the Schliemann archive (outgoing correspondence from 1845 to1890) belonging to the Gennadious Library in the School of Classical Studies in Athens, Greece. A selection of pages has been examined in ultraviolet reflection and fluorescence conditions, as well as in the near infrared region of the spectrum using infrared reflectography techniques, in normal and macro mode. The aim of research was to outline a non-destructive methodology to record the condition of the copy letters. Six categories were set by the comparison of the quality of the copies, the state of oxidation and their optical behaviour in different wavelengths. The results of this study showed that the proposed non-destructive methodology can contribute to the legibility of the text, the distinction between the phenomena of oxidation and diffusion on the inked areas, the precise recording of the oxidised areas and the collection of indications in terms of the quality of ink. Factors influencing the outcome of the copying process are also discussed.