32.2 Chemistry and Research – AgarArt and modern wall paintings related issues

05/10/12

It may happen that the cleaning of a wall painting is more problematic than the restoring of an ancient fresco. That is the case of the mural called “Tuttomondo” by Keith Haring, painted in 1989 in Pisa [1]. A preliminary diagnosis and the next restoration were part of COPAC (Conservazione Preventiva dell’Arte Contemporanea), an important project focused on preservation of contemporary art works, financed by Tuscany Regional Administration, under the supervision of Prof.ssa Maria Perla, from the University of Pisa.
The wall painting was suffering from the effects of urban pollution and covered by a film (thin layer) of calcium carbonate (from the recrystallization process) that made the original colors dull. The restorers, Mr.Antonio Rava and Mr.Will Shank had to address a number of problems when cleaning that work:
  • organic solvents were not allowed, because those agents would have reacted with the acrylic substrate
  • They could not adopt moistening pads nor rinsing operations because water, when migrating through the layers of the wall, activates the reactions of salts
  • Wishab rubber and natural rubbers could not be applied because of the residuals and other minor issues
Therefore they tested and implemented the spreading of hot-melt agar agar. They got the best results by using 5% of AgarArt in a solution of EDTA at 1%, neutralized by 0.2% of ammonium carbonate, added at 45°C. Once the gel is removed, it just takes off the opaque patina, without damaging or lifting any fragments of paint. (showing to be as gentle as expected).

In order to get good results it is important to remember that depends on the paint color.

Preliminary tests suggested:
-time=10 min for aquamarine, turquoise and pink (EDTA could be reduced to 0.5%);
-time=30 min for red and white.

The set-up of that Agar Art technique was supervised by Anzani e Rabbolini from Acconerre Studio, who already faced similar issues when operating on a large mural (120 m²) of the apse of S.Eugenio Church, Milan, painted by Baruzzi in 1960. 
During the restoration of that fresco, Andrea Toniutti had to clean without water. In fact, he was afraid of causing the migration of sulphates in the substrate because of the presence of gypsum beside the lime.

As a matter of fact, calcium sulphate is really sensitive to humidity and moisture itself decrease the mechanical resistance of the texture. Therefore, they decided to adopt solid gel, with minimum release of water.

The choice of Agar gel was fully satisfactory: no damages on the surface, no sulphate migration from the substrate, no mechanical stress on the painting when removing the deposits.

A step by step procedure was followed. Firstly they removed big particles of dust, then cleaned the surface deeper and deeper. For such purpose they adopted a mixture of Agar Art at 4% in water with tri-ammonium citrate (1%) for 20~30 minutes. Chelation agent enables the cleaning mixture to take out stains and dirty traces.
The pictures show the spreading of liquid Agar Art at 45°C and the removal of the film blackened by the dirty stuff. (no pigments detected in the film….that means the treatment is severe with dirt and gentle with paint)


References
1-A. Rava, W. Shank, P. Colombini, O. Chiantore, M. Picollo, V. Palleschi et alii "Keith Haring a Pisa. Pulitura e protezione di un dipinto acrilico esposto in ambiente esterno”.Scienza e Beni Culturali XXVIII (2012) 
2-M. Anzani, L.Borgioli, A. Rabbolini, A. Toniutti; "S.Eugenio a Milano, 120 mq di pulitura ad Agar Agar”, Atti del IX Congresso IGIIC "Lo Stato dell’Arte 9”, Cosenza, 13-15 ottobre 2011.

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