JAIC 1986, Volume 25, Number 2, Article 3 (pp. 83 to 92)
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Journal of the American Institute for Conservation
JAIC 1986, Volume 25, Number 2, Article 3 (pp. 83 to 92)

ON THE REVERSIBILITY OF TREATMENTS WITH ACRYLIC/SILICONE RESIN MIXTURES

A.E. Charola, A. Tucci, & R.J. Koestler



2 EXPERIMENTAL


2.1 Sample Preparation

Two limestones were used for this study, an oolitic one, Indiana limestone, and a fossiliferous one, from Vicenza, Italy. Cubic samples (5 5 5 cm) were treated with a mixture of acrylic and silicone resins. The samples were treated by capillary rise with the following mixture:

  • 15% v/v of 30% w/v Acryloid B72 (Rohm & Haas) in 1:1 toluene-xylene mixture
  • 5% v/v of 70% v/v DriFilm 104 in white spirit
  • 40% v/v 1,1,1 trichloroethane
  • 40% v/v acetone
The samples were left in contact with the mixture for about 18 hours. The increase in weight due to the resin mixture uptake was 0.7% for the Indiana limestone and 1.5% for the Vicenza limestone, which is more porous. More details on the sample preparation technique and on the resulting change of porosity and size distribution are given elsewhere.11


2.2 Accelerated Weathering

Some of the samples were weathered by repeated cycles of sulphuric acid fog (4 hours) followed by drying in a climatic chamber (20 hours). The samples were subjected to 21 cycles in total. Acid fog was obtained by means of a 0.02 M H2SO4 solution. About 0.01 ml/cm2 of acid solution collected per hour on the horizontal face of the sample (the face that had been in contact with the mixture during the treatment, referred to from here on as the top face). The climatic chamber was equipped with a 125 W UV lamp, of high pressure mercury vapor, with highest emission at 280–380 nm, which was left on during the length of the exposure in the chamber at 50C and 70% RH. More details on the accelerating weathering have been reported previously.11,12


2.3 Extraction of the Applied Resin

The applied resin was extracted from weathered and unweathered specimens by two methods:

  1. poulticing with a cotton pack holding a 1:1 acetone-trichloroethane mixture, applied over tissue paper on the top face. The pack was left for 1 hour, and the treatment repeated three times;
  2. immersion of the whole specimen in a 1:1 acetone-trichloroethane mixture and left for four days. The solvent was then changed and left for another seven days.


2.4 Infrared Analysis of Extracted Residues

IR spectra were obtained by forming a film on a NaCl plate from the solvent solution obtained from either the poulticing or the total immersion of the sample.


2.5 SEM examination

Samples of specimens of the outer surface of the untreated limestones, treated, and treated and weathered, were examined under SEM. The last two types of samples were also examined after poulticing or immersion extraction had been performed. The specimens were mounted on appropriate stubs and sputter-coated with 10nm of gold.


Copyright 1986 American Institute of Historic and Artistic Works