Stone Portal, 16th century
Church of the Holy Annunciation, Dubrovnik, Croatia

The portal was made in 1534 by the sculptor Petar Andrji using calcareous stone probably brought from the island of Korcula. It is anchored by two double pilasters with rosette motifs surmounted by semi-capitals decorated with finely carved leaves. The round arch is decorated with two overlapping bands with vegetal motifs. A pediment above the arch frames the bust of an angel praying.
The stone surface was covered with a black crust. An ocher patina, caused by various types of lichen was evident on the surface. The pediment had a thick greyish patina of biological origin, which had penetrated the under layer of the stone causing not only aesthetic but also chemical damage. Plants had taken root on the masonry face near the doorway, and their roots likely created mechanical pressure and cracking. A sulphuric acid attack had been triggered by atmospheric pollutants with consequent deterioration of the surface. A worrying and rapidly increasing loss of material was apparent above the arch. Cracking and small losses of material were evident everywhere, many of them caused by shrapnel from grenades exploded during the war of 1991. The structures were separated and loose. The entire stone surface was initially dusted and washed. Repeated compresses of cellulose pulp soaked in an ammonium carbonate solution were initially applied on the areas affected by the black crust. The stone surface exposed to biodeteriogenic activity was treated chemically.
Some sculpted fragments poorly anchored to the stone surface were reinforced and attached. Various injections of epoxy resin were made in the deepest cracks.
In agreement with the director of works it was decided to insert a stone gusset in the architrave of the portal, imitating the original, using local calcareous stone. This was then glazed with a light paint, using Siena and natural umber earth powders.
The old, now loosened fillers were mechanically removed using scalpels and replaced with new fillers of lime, local stone dust and sand, and made level with the stone surface.