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6 June 2011

Saturday 4th June 2011; Venice

Week 8 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation 
The Study Tour: Venice

This morning we took a boat to the Piazza San Marco where we met Paolo Pagnin again (see Friday 3rd June 2011; Venice) to discuss and visit the site he is currently working on in the Piazza; Procuratie Vecchie. We were given a presentation on the work being carried out on site by a member of Paolo's team and by the site architect. The building spans 54m along the northern side of the piazza and is 19m high. Construction began from the eastern end in 1513 and was completed at the western end in 1538; it is the oldest building in the piazza and is very unusual in that it has structural stonework which can only be found in one or two other Venetian buildings.

View of Piazza San Marco from the Canale della Giudecca.

The Procuratie Vecchie in the centre and right-hand side of the photograph.

View of  Basilica Cattedrale Patriarcale di San Marco at the eastern side of the piazza from the scaffolding on the Procuratie Vecchie, which is also visible extending along the left-hand side of this photograph.

The project currently underway is to conserve the historic facade of the structure and the architect described the aim of the work as 'to conserve the first layer of patina below the crust'. Extensive documentation has been carried out prior to the start of any work. The method being used on site for removal of the black crust (following tests) and as specified by the architect is a biological poultice which is a combination of urea, glycerine and water. The use of this technique has to be well timed because the pH of the poultice has to be controlled and kept below 10; after 10 days the pH of the solution can rise rapidly to 12. Some thicker areas of black crust are being scraped back using a scalpel as an initial stage. After the poultice is removed the surface of the stone is being brushed and sponged with water and some focussed laser cleaning is being carried out in specific areas. The facade is tied into the building by chains and iron fixings around some of the columns. Where possible these are being retained and treated with an anti-rust treatment but some are too decayed and will have to be cut through and replaced. In some areas it was possible to look into the ceiling space and observe the back of a lath and plaster ceiling. Paolo told us that on the other side is a fresco ceiling. The lath is made from a type of bamboo that can be found in the lagoon.

One of the capitals following removal of the black crust. A red-brown patina was discovered on all of the capitals at one level and it was decided that this was the desired level of cleaning. An iron tie which is attached to a chain holding the facade in to the floors is visible in this image.

A capital still in it's original state prior to cleaning.

View inside the structure into a space above a ceiling showing the lath and plaster rivets.

After the site visit we had a few hours free time to walk around the city, a couple of observations are below.

The water-side facade of a building showing the large amount of damage caused by the rising water from the constantly saturated part to the salt deposits and damaged brickwork and the almost total loss of render.

A beautiful example of the location and formation of black crusts. We have been told that black crusts develop in areas that are protected from water (rain fall) and it is quite clear here that the exposed parts of the building are white and the sheltered parts below the cornices are black. The faces must protrude just far enough that they have been washed clean and stand out in great contrast to the sheltered areas of black crust.

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