Application example: Insights into the production techniques of Art Nouveau glass

Iridescence is complex optical phenomenon in layered surfaces, used to impressive artistic effect in Art Nouveau glass by manufacturers like Tiffany and the Austrian company Loetz around 1900. Several fabrication approaches can be followed to obtain the iridescence effect, offering a way to distinguish products from different manufacturers and to identify imitations and forgeries. To these ends, a non-destructive method for depth profiling of the material is required. Combining the ion beam analytics methods of PIXE (proton-induced X-ray emission) and RBS (Rutherford Backscattering) the composition of iridescent Loetz glass could be determined in great detail.

The fabrication process for iridescent glass in the Loetz manufacture had several steps: The hot glass slug was first rolled in splinters of a different glass type. The object was then reheated and blown into the intended shape, embedding the splinters in its surface in the process. Subsequently, the object was sprayed with solutions of tin chloride or metallic salts. After the final annealing, a pattern with iridescent spots from the splinters, called a Papillon pattern, is obtained.
This procedure results in the following material structure, as determined by ion beam analytics: The bulk of the object is potash-lime-silica glass. It is covered by an overlay glass consisting of silicon oxide with lead, silver, calcium, and potassium. The inclusions of the splinter material with higher content of lead and silver are limited to the overlay glass. The spraying with tin chloride solution produced a thin top layer of tin oxide with around 50 nanometers thickness. Some tin diffused from the top layer into the overlay glass during the final annealing step.

Iridescent glass, whether by design or by corrosion, is a material with a highly complex layered structure. Ion beam analytics reveal the details of the layered glass structure resulting in the iridescence effect without the need for mechanically preparing a cross-section.

• D. Jembrih-Simbürger et al., X-ray fluorescence and ion beam analysis of iridescent Art Nouveau glass – authenticity and technology.
  Nuclear Instruments and Methods in Physics Research B 226 (2004) 119
  https://doi.org/10.1016/j.nimb.2004.03.075