POLYMER TREATMENTS FOR STONE CONSERVATION: METHODS FOR EVALUATING PENETRATION DEPTH
FRANCESCA CASADIO, & LUCIA TONIOLO
3.1 STONE TREATMENT
Suitable stone samples, measuring 50 x 50 x 20 mm, were smoothed with abrasive carborundum paper (180 grit), washed with deionized water, and dried until constant weight was reached. Then the samples were treated by capillary rise absorption with solutions of the three different products: a 5% w/w solution of Paraloid B-72, a 5% w/w solution of TFEMA/MA, both in ethyl acetate, and an 8% w/w solution of Wacker 290 in white spirit. Treatment time varied from six seven hours, depending on the porosity of substrate. The quantity of polymeric material impregnating the stone specimens as a result of the treatment is reported in table 1.
3.2 TECHNIQUES OF ANALYSIS
Depending on the type of investigation performed, samples were prepared in two different ways for depth-profiling: treated samples were cut with a diamond precision saw (Struers Minitom) either as sections measuring 10 x 15 x 2 mm with plane surfaces parallel to the impregnated outer surface, or as cross sections, sawing along the direction of capillary rise of the solution, i.e., perpendicular to the treated uppermost surface (fig. 1).
Cross sections were investigated with the following techniques:
- micro-ATR spectroscopy: performed with a FTIR Spectrophotometer Perkin Elmer Spectrum 2000 equipped with nitrogen-cooled MCT detector and microscope with video camera, motorized stage, and germanium (Ge) crystal micro-ATR accessory
- static contact angle measurement: executed with a Lorentzen and Wettre instrument, modified with tilting sample holder. Sections were investigated with the following techniques:
- diamond cell FTIR spectroscopy: performed with a FTIR Spectrophotometer Perkin Elmer 1725x equipped with DTGS detector and Graseby-Specac diamond cell accessory
- TG-FTIR: carried out with DuPont Instruments thermal balance 951 coupled to a FTIR Spectrophotometer JASCO FT/IR 420, equipped with interchangeable DTGS and MCT detectors and White's gas-cell with an optical path length of 120 cm.