The portable icon of Saint Thomas the Apostle (dimensions 165x59x6 cm.) is housed at the Ecclesiastical Museum of the Holy Metropolis of Thessaloniki and dates to the 17th century. 

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Before conservation treatments, a diagnostic test incision was made into the painted surface of the icon. It revealed that the surface was overpainted, while the layer of original painting had been gilded. 

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​Non-invasive techniques then followed, including macroscopic observations with imaging techniques: ultraviolet fluorescence photography and infrared reflectography. An examination and macroscopic observation of the icon was performed, followed by documentation of damages and their state of preservation. 

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​After evaluation of the results of the scientific examination, the conservation methodology for the icon was developed. It was revealed that the portable icon had been overpainted even in places where there was no damage or missing pieces; thus, it constituted an entirely new work. 

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​The original painted surface had a layer of primer (backing support), whereas the newer layer had been painted directly onto the varnish of the first painted layer. The process of revealing the original painting revealed the gilded, polished surface of the background. The work displayed cracks in its painting, which also included losses in color. 

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During the conservation treatments, the primer (backing support) was stabilized so as to avoid further detachment and the cracks were levelled. The panel was strengthened and technically reinforced, and then followed the process of aesthetic restoration. These procedures completed the process of unveiling the work, always with respect for the authentic creation, its historicity and originality by maintaining the basic ethical principles of conservation: minimal intervention, reversibility and readability.