Corpus Vitrearum - Centre André Chastel

lundi 3 juilletRésumés des communicationsLisa Pilosi, Mark Wypyski,Sarah Barack and Drew AndersonEarly Acid-Etchingof Stained Glass : the Written EvidenceFig. 1 New York,The Metropolitan Museum of Art (accession number1996.262. Ruth and Victoria Blumka Memorial Fund and TheCloisters Collection, 1996) : Adoration of the Magi, circle of theStrassburger Werkstattgemeinschaft ; 1507.The selective removal of the colored layer of flashedglass by etching with nitric acid is described in theearly fourteenth century treatise of Antonio da Pisa 1and in the fifteenth century Bologna Manuscript 2 .To amodern reader, this seems like an impossibility sinceonly hydrofluoric acid will etch modern glass.Nevertheless, a number of acid-etched panels havebeen identified throughout Europe,which predate the« official » discovery of hydrofluoric acid in the lateseventeenth-eighteenth century. A sixteenth centurysouthern German donor’s letter specifically calls forthe use of etching in the coats of arms,suggesting thatthe technique was known amongst stained glasscraftsmen of the time 3 .This gives rise to two (not necessarilymutually exclusive) possibilities - that nitricacid will etch glass and/or that hydrofluoric acid wasused much earlier than previously thought. In fact,several informal experiments have shown that nitricacid will etch glass with a relatively low silica and relativelyhigh lime content 4 . In addition, from the seventeenthcentury on, numerous texts describe thedissolution of the mineral fluorite in sulfuric acid andits corrosive effect on glass 5 .The exploitation of fluoritemines in central Europe from the fifteenth centuryand the contemporary use of fluorite as anartist’s pigment, coupled with the occurrence of acidetchingin stained glass panels from the same regionsuggests some sort of connection.This study investigates the techniques of etching glassdescribed in the historic treatises.Model glasses wereproduced with specific compositions to mimic anaverage potash glass typically encountered in medievalwindows and a high lime potash glass (that correspondsto the etched glass on a panel depicting theAdoration of the Magi, by an artist of the circle ofthe Strassburger Werkstattgemeinschaft, dated1507 in The Metropolitan Museum of Art) (Fig. 1).Etching trials using nitric acid and fluorite/sulfuricacid were conducted in a controlled laboratoryenvironment. Scanning electron microscopy andX-ray microanalysis were used to characterizethe effectiveness of the process (i.e. the depth ofetching), the morphology and any chemical changesevident on the etched surfaces.1. Vetrate Arte e Restauro : dal Trattato di Antonio da Pisa alle nuovetecnologie di restauro, Milan, Silvana Editoriale, 1991.2. Merrifield (Mary P.), Original Treatises on the Arts of Painting, vol. 2,New York, Dover Publications Inc., 1967, chapter 217, p. 494-495.3. Schleif (Corine) and Schier (Volker), « Views and Voices fromWithin : Sister Katerina Lemmel on the Glazing of the Cloister atMaria Mai », Glasmalerei in Kontext : Bildprogramme undRaumfunktionen : Akten des XXII Colloquiums des Corpus Vitrearum,Nürnberg 29. August-September 2004 (Anzeiger des GermanischenNationalmuseums, wissenschaftlicher Beiband 25), éd. RüdigerBecksmann, Nüremberg, 2005, p. 6.4. Verità (Marco), « Commento Tecnico al Trattato di Antonio daPisa », Vetrate Arte e Restauro, op. cit note 1, p. 99-100 ; Scholz(Hartmut), Hess (Daniel), Rauch (Ivo), Kölzer (Norbert) andWindelen (Barbara), « Beobachtungen zur Ätztechnik an Überfanggläserndes 15. Jahrunderts », Corpus Vitrearum News letter, 46,1999, p. 19-23.5. Charleston (Robert J.), « Part 5-Acid Etching on Glass », TheGlass Circle, no. 3, 1979, p. 31-39 ; Cassebaum (Heinz), « NeueAspekte zur Entdeckung des Ätzens von Glas », Silikattechnik, 34,Heft 7, 1983, p. 213-215.16