Stucco Relief from Structure XIX, Palenque

Treatments Applied

1. Loosening of the pilaster.

• Fixation of the pictorial layer:
  The pigment was fixed using Paraloid B72H, in a 5% concentration, applied by sprinkling.

• Partial covers:
  Loose fragments were partially covered with Japanese paper, using Paraloid B72H, in a 5% concentration, with acetone as the adhesive agent (see photo 10).

  
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• Protection cover:
  This procedure was carried out by using a first insulating layer of a cheesecloth cover adhered with Paraloid B72H at a concentration of 3% in acetone, and by further placing another layer of China paper using Paraloid B72H at a concentration of 5%, to stick it together (see photo 11).

  
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• Insulating layer:
  Aluminum foil was used as an insulating layer on the entire relief surface, after verifying that the foil was free of perforations (see photo 12).

• Provisional support:
  The provisional support consisted of a rigid layer of polyurethane foam which was injected between the stucco and a wooden frame so that the support would acquire the shape of the relief, thus preventing any movement during its transportation to the restoration workshop (see photo 13).

  
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  Once the polyurethane foam catalyzed, the provisional support was moved, and with the plank’s weight and the lack of any adherence between the stucco and the pilaster, the stucco came off.

2. Transportation of materials to the restoration workshop.

   
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• Once all the materials were taken to the lab, they were sorted according to their point of origin, separating those that were found among the rubble (see photo 14, above, and photo 15), and the fragments detached from the pilaster (see photo 16); then, according to this classification the processes of cleaning, consolidation and assembly of the fragments was undertaken, according to the requirements of each piece. Later, a separation and preliminary grouping of materials was carried out depending on shapes, colors, paste types and their thickness (see photo 17, below, and photo 18).

  
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3. Superficial dry cleaning.

• Stucco fragments found in the rubble:
  These fragments underwent the superficial, mechanical cleaning processes, by means of soft brushes, small brushes, a surgical knife, a dissection needle and a small pear-shaped air pump to remove clay, carbonates, and organic material remains such as roots (see photo 19).

• Detached fragment:
  On the reverse of this fragment a superficial, mechanical cleaning was completed, using soft brushes, small brushes, a surgical knife, a dissection needle and a small pear-shaped air pump to eliminate clay, soluble salts and non-stucco materials, such as organic remains, stones, etc. (see photo 20).

4. Chemical cleaning.

• In the next step, a chemical cleaning was carried out on the fragments recovered from the rubble using a 1:1 solution of water and alcohol, applied with smooth hyssops to eliminate clay and soluble salts (see photo 21).

  
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5. Consolidation.

• Fragments found within the rubble:
  This process was applied only to the most degraded fragments. Paraloid B72H was used at a concentration of 3%, dissolved in thinner and applied by dripping.

• Detached fragment:
  The consolidation process of the stucco support was done using Paraloid B72H, at a concentration of 3% in thinner, by dripping through venoclysis, and then with the application of sprinkled alcohol to disrupt the surface tension, inside a slow-dryer chamber (see photo 22).

6. Consolidation of cracks and fissures:

• A solution of calcium caseinate was injected on the reverse of the fragment detached from the jamb of the pilaster (see photo 23).

7. Repairs on the reverse of the detached fragment.

• With the surgical knife, the back side of the detached piece was leveled, lowering the most pronounced protuberances in order to obtain a surface as uniform as possible; then, the cracks, fractures and fissures were repaired with a repairing paste made of lime and fine limestone powder in a proportion of 1:2 (see photo 24, below, and photo 25).

  
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8. Insulating layers in the detached fragment.

• 2 layers of calcium caseinate:
  Once the repair dried up, two layers of calcium caseinate were applied with a soft-haired brush.

• 1 covering with cheesecloth and calcium caseinate:
  This process consisted of one covering made of double cheesecloth, in addition to calcium caseinate applied with a brush so as to stick the cloth and the stucco together (see photo 26).

  
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• 1 covering with a Guadalajara cloth and calcium caseinate:
  Later, a second covering was accomplished with Guadalajara cloth and calcium caseinate (see photo 27) applied with a brush, attaching it to the cheesecloth to avoid air bubbles (see photo 28).

  
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• 2 layers of folded tissue paper (see photo 29):
  Then, a provisional insulating layer of tissue paper was applied, which was adhered by humidity (see photo 30). Once this layer dried up, cardboard retainers were added to maintain the provisional support in place (see photo 31).

  
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9. Provisional support.

• Plaster with polystyrene pearls:
  Once the layer of tissue paper dried up, a plaster layer with a load of polystyrene pearls was applied (see photo 32) to make this layer lighter, functioning at the same time as a provisional support (see photo 33).

  
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• Plank in the shape of the stucco:
  When the plaster dried up, a plank in the shape of the stucco was added, to provide the panel with a greater support (see photo 34).

Then it was tied up to the plank (see photo 35) and turned over (see photo 36), and:

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We proceeded to remove the insulating layers with which the stucco relief was detached from the pilaster of Structure XIX (see photo 37), which were as follows:

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1. A plank, as a provisional support (see photo 38).

   
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2. The layer of polyurethane foam (see photo 39).

   
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3. The layer of tissue paper.

As soon as the layers of the detachment were removed, we proceeded with a superficial dry cleaning using a soft-haired brush to eliminate the powder and the clays on the surface (see photo 40).

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Then a chemical cleaning with smooth hyssops while the partial covers of Japanese paper were eliminated (see photo 41); subsequently, the cracks and fissures were injected with calcium caseinate.

Once the calcium caseinate was dry, repairs were made with lime paste and stone powder, ¹   and parallel to this process, the small fragments of loose and detached pastillaje that were in place were re-assembled with Mowithal B60H.

Endnote:

¹  Throughout this process, the repairing paste traditionally used for mural paintings on stucco was used; as the restoration process continued and extreme climatic changes took place, we realized that this type of paste for repairs was not the most appropriate one for this particular relief, and therefore the decision was made to use ceramic repairing paste.

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