Non-invasive methods for characterising letterpress prints: Surface microscopy and profilometry

• Characterisation of letterpress prints through non-invasive analysis. • Morphological comparison between prints from different periods. • 3D techniques for analysing type-form relief. • Useful tool for conservation, restoration, and cataloguing. • Supports dating and authentication of letterpress cultural heritage. This study presents a methodological framework for characterising letterpress prints by combining morphological analysis with three-dimensional measurements. Original prints, as well as controlled mock-ups produced in the laboratory were analysed with surface microscopy to assess ink distribution on the paper. Optical profilometry was used to quantify the reverse embossing generated in the paper by the type-form. Results show that the various methods and materials employed for letterpress printing over time lead to differences regarding ink distribution and relief levels. These are described and presented as key identification features through which the origin of early and contemporary letterpress prints can be determined. The paper provides visual examples of the traits that letterpress prints can show throughout history and establishes a methodological approach for their characterisation. Therefore, this research expands the range of methodologies available for the technical cataloguing of letterpress prints.