CAITLIN SMITH | GRADUATE PROGRAM IN HISTORIC PRESERVATION | UNIVERSITY OF PENNSYLVANIA

CLEANING METHODS FOR THE REMOVAL OF

LIMEWASH FROM PAINTED PLASTER SURFACES:UTILIZING ION EXCHANGE RESINS ON THE INTERIOR ARCHITECTURAL

FINISHES OF THE CAPILLA DE NUESTRA SEÑORA DEL ROSARIO IN

IGLESIA SAN JOSÉ, IN SAN JUAN, PUERTO RICO

USF C-211 HLewatit CNP 80 (H) USF C-211 (Na)Lewatit TP 207 (Na)

Ion exchange resins viewed at 115x magnification on a Leica MZ16 stereomicroscope (Source: C. Smith, 2009).

METHODOLOGY

Work began with research into the church, the materials, the conditions, and traditional methods of

limewash removal. After establishing these parameters, the focus shifted to ion exchange resins. Ion

exchangers are, on their most basic level, atom exchangers activated by water solutions. Today,

commercial distributors sell them as microspheres. These ion exchange resins are insoluble organic

polymers that can take up the positive and/or negative ions of compounds they come into contact with,

exchanging them for cations or anions [3], [4]. The resin type is determined by the type of ion that the

material exchanges (cationic +, anionic -, mixed) [5], and they are classified as either weak or strong,

based on the strength of the acid or basic groups present [6]. When surrounded by water, the resins‟

fixed ionic groups become ionized and swell, freeing water molecules and exchangeable ions to migrate

[4]. The ions are traded stoichiometrically, meaning it is an even exchange where the amount of ions

removed from a material are replaced with the exact same amount of ions [3], [4]. Today‟s synthetic

resins can be used repeatedly, they are insoluble and can be regenerated back to their original form [5].

This makes them an attractive treatment option, as it allows for long-term use and re-use of the resins.

From this research, a testing protocol developed to evaluate the performance of four different ion

exchange resins. The resins were selected from two U.S. companies for the following properties: [6], [7]

Using this as a guide, a hydrogen-form and a sodium-form resin were selected from each company.

The hydrogen resins should be more aggressive, as calcium ions in limewash exchange with hydrogen

ions in the resin to form carbonic acid. The sodium resins should be less aggressive and more pH

neutral. Sodium bicarbonate is formed when the calcium and sodium ions exchange. All four are

cation exchange resins capable of exchanging calcium ions.

Non-aggressive

Selectively targets calcium ions

Replaces with innocuous ions

Large matrix

No strong acids

Neutral pH

Effective with additives

Gel or poultice treatment

High exchange capacity

LITERATURE CITED

[1] Johnston, Kerry L., and Cynthia L. Silva. “La Capilla de Nuestra Señora del Rosario, Iglesia San José, San Juan,

Puerto Rico: Interior Finishes Investigation and Conservation Treatment Plan.” Philadelphia, Pa.: The Architectural

Conservation Laboratory, School of Design, University of Pennsylvania, September 2008.

[2] Silva, Cynthia L. “A Technical Study of the Mural Paintings on the Interior Dome of the Capilla de la Virgen del

Rosario, Iglesia San José, San Juan, Puerto Rico.” Master‟s thesis, University of Pennsylvania, 2006.

[3] Fiorentino, P., M. Marabelli, M. Matteini, and A. Moles. “The Condition of the „Door of Paradise‟ by L. Ghiberti. Tests

and Proposals for Cleaning.” Studies in Conservation 27, no. 4 (November 1982): 145-153.

[4] Zagorodni, Andrei A. Ion Exchange Materials Properties and Applications. Oxford, UK: Elsevier BV, 2007.

[5] Berlucchi, Nicola, Ricardo Ginanni Corradini, Roberto Bonomi, Edoardo Bemporad, and Massimo Tisato. “‟La

Fenice‟ Theatre – Foyer and Apollinee Rooms – Consolidation of Fire-Damaged Stucco and Marmorino

Decorations by Means of Combined Applications of Ion-Exchange Resins and Barium Hydroxide.” In Proceedings

of the 9th International Congress on Deterioration and Conservation of Stone, Venice, June 19-24, 2000, vol. 2,

edited by Vasco Fassina, 23-31. Amsterdam, The Netherlands: Elsevier Science B.V., 2000.

[6] Guidetti, Viviana, and Maciej Uminski. “Ion Exchange Resins for Historic Marble Desulfatation and Restoration.” In

Proceedings of the 9th International Congress on Deterioration and Conservation of Stone, Venice, June 19-24,

2000, vol. 2, edited by Vasco Fassina, 327-333. Amsterdam, The Netherlands: Elsevier Science B.V., 2000.

[7] Giovagnoli. A., C. Meucci, and Marisa Tabasso Laurenzi. “Ion Exchange Resins Employed in the Cleaning of Stones

and Plasters: Research of Optimal Employment Conditions and Control of their Eff ects.” In Deterioramento e

Conservazione della Pietra: Atti del 3 Congresso Intemazionale, Venice, October 24-27 1979, 499-510. Padova,

Italy: Instituto di Chimica Industriale, Università degli Studi di Padova, 1982.

RESULTS

Three small-scale tests were conducted in the laboratory to determine whether or not the resins have

any effect on limewash, whether the type of resin changes the results, whether they are more effective

than water and traditional cellulose poultice treatments (which were also the controls), and to determine

an approximate number of applications required to remove limewash layers.

In the tests, the hydrogen-form was confirmed to be acidic (note the pH indicator turned red), the

sodium-form resins to be highly alkaline, and interaction with the limewash actually caused the

formulates to become more basic. It was unclear how much of the dimensional change came from the

formulates. The paint chips were often broken during handling. As far as their efficacy in removing

limewash, these particular resins, in their ready-made form, were not strong enough to completely break

down a limewash layer, but that they could, over time, cause it to degrade.

In the second test for formulate efficacy, a mixture suitable for both building conservation and

maximizing ion exchange was created. The mixture needed to retain water so that the resins would stay

activated, have resistance to flow, good adhesion to substrates, good adhesion to inclined surfaces,

easy application, and be easy to control. After testing, one formula was selected for further trials.

FOR FURTHER INFORMATION

Please contact caitlinesmit@gmail.com. More information on this and related projects can be obtained

at http://www.conlab.org/. A full text PDF of this thesis is available at Scholarly Commons,

http://repository.upenn.edu/hp_theses/121/.

None of the formulas produced enough deterioration to make limewash cleaning by ion exchange resin

a practical option. In their current formulas, the resins would only be useful in treating very fine lime

haze and in areas where a very gradual, controlled cleaning is required. Further testing is necessary to

determine which preconditioning, additives, and mixture ratios maximize the exchange process.

Changes in temperature, RH, and resin type should be included as variables. Resin matrix type and

size, counterion charge, resin strength, and pH are all factors. Testing should be done on samples with

a design layer and plaster substrate to look for color changes, pH changes, and deleterious byproducts.

In the first test, to confirm

whether resins have any

effect on calcium

carbonate (limewash)

molecules, pure resin

mixtures, containing only

resin, distilled water, and

pH indicator, were

created. Limewash paint

chips were completely

submerged in the

formulates. They were

examined at regular

intervals. These results

were recorded in tables

to allow for sample

comparisons over time.

The third test incorporated a substrate,

to see how ion exchange resins

perform in a less-optimal environment.

Five versions of the same formula were

made, one for each type of resin and a

control. The formulas were applied to

a limewash covered tile at one hour

intervals. After six hours, three of the

five test areas showed microscopic

changes in texture. The table below

shows the results. Once again, the

hydrogen-form resins proved more

acidic and stronger than the other

resins. The control caused no

significant deterioration. The sodium-

form resins, on the other hand,

performed differently in tests one andthree. This could be due to operator error, sample error, or a side effect of the formulate additives.

CONCLUSIONS

The field of ion exchange technology promises to continue to bring new technologies and new

opportunities for less destructive cleaning and testing methods. Benefits of the technique include: no

material is lost from the reaction itself; the resins are non-hazardous and can be easily handled and

transported; the exchange reaction only occurs at the interface between the resin and the substrate;

dwell time, rheological additives, and limited reactivity depth give conservators a large degree of control;

they can double as consolidators and desulfators; detrimental ions can be replaced with innocuous ions.

However, conservators should also be aware of the disadvantages: the resins only act on the surface

they are in contact with, necessitating multiple treatments for highly concentrated substances; the

reaction is slow, requiring dwell time, constant moisture, and repeated applications; resins can be

quickly rendered ineffective; resins may be too acidic or alkaline for sensitive historic finishes; the

exchangeable counterion needs to be chosen carefully to prevent the creation of undesirable

byproducts; the resins may be too costly, time-consuming, and require pre-conditioning to be effective.

Ion exchange is a relatively new technique for cleaning painted and plastered surfaces. A great deal

more testing and re-evaluation needs to occur before conservators can claim that ion exchange resins

are suitable and safe for cleaning wall paintings. Nevertheless, heritage sites like Iglesia San José

continue to strive for less destructive, less invasive, and more sustainable treatments. The versatile

nature of ion exchange cleaning suggests that it will play an important role in this process.

INTRODUCTION

La Iglesia San José is a sixteenth-century church in San

Juan, Puerto Rico. Due to a lack of maintenance and

growing structural problems, it closed in 1998. Within the

church, a team from the University of Pennsylvania

examined the seventeenth-century Capilla de Nuestra

Señora del Rosario (Rosario Chapel). The Chapel

contains a series of six mural campaigns, layered

successively on top of one another and in a highly

deteriorated state. Interventions improved roof drainage,

ventilation, and stabilized detached plaster, but moisture

infiltration/condensation, chloride salts, and biological

growth remain a chronic problem for the Chapel. This

leads to areas of detachment between the plaster layers,

and between the lime plaster and the wall structure.[1] [2]

A decision was made to take the Chapel back to its first

and most complete painting campaign. A series of

mechanical and chemical cleaning tests on the Chapel‟s

fragile lime plaster surfaces and powdering matte paints

were largely successful at removing limewash

overpaintings. However, there were places where the

techniques proved too aggressive and ineffective at

removing lime haze. A technique involving ion exchange

resins could offer a safer and more effective cleaning

method than mechanical means of removing limewash

overpaintings, by targeting calcium ions in the limewash

compound and replacing them with a material that is

more easily removed.

Mechanical cleaning

of la sirena in

Rosario Chapel [1].

Ion exchange resin USF C-211 Na in water with

transmitted light at 50x magnification on a

compound microscope (Source: C. Smith, 2009)