Characterization of pink biological patina in calcareous stone

Some of the interior walls of the Church of São João de Almedina, as well as some polychrome limestone sculptures and retables in the Museum, show a pink patina, also observed in other Portuguese monuments. A study carried out in 2003, in collaboration with the Department of Conservation and Restoration of the Universidade Nova de Lisboa, allowed the attribution of a biological origin to the patina and its scientific characterization.

In sample areas different biocides were tested and the microorganisms present were identified. The efficiency of the treatment was periodically evaluated by macroscopic observation. Future measurements of the colour parameters will be carried out and new samples will be taken in order to qualify and quantify the presence of microorganisms and to confirm the long-term efficiency of the biocides in the stone. A daily control of the monthly variations of the relative humidity and the air temperature in the church is being carried out in order to check the bio-susceptibility of the location.


From the second quarter of the 16th century the achievement of this great master was extraordinary, not only for the work that he left, but also because of the training of generations of sculptors who passed through his workshop and who, subsequently, were to establish themselves all over Portugal. Also remarkable is the vast satellite production which spread throughout the region of the Lower Mondego and which reached various parts of the country.

The aim of this project is to identify the stratigraphy of the pictorial layers, original or not, and the materials used in their execution. Other objectives are to partially recuperate the lost art of the manual production of colours and reconstitute the techniques used. In cases where the period when the pigments were in use is known, the chronology of the interventions and the authenticity of the work can be determined. This systematic study will allow art historians to produce scientifically proven arguments thus making progress in the history of the techniques of artistic production.