Electrolytic Cleaning of Silver Threads -Effects of Electrolytes on the Condition of Silk

Abstract

This thesis investigates localised electrolytic reduction as a method to clean tarnish on silver threads on silk. The tool used is an electrolytic pen called the Pleco that was developed for local treatment of metals on composite objects. Silver embroidery on silk fabric is typically left uncleaned because me-chanical and chemical corrosion removal methods can be harmful to the silk. There is currently no widely accepted method to clean silver on silk. The main focus of the study was the assessment of the condition of silk after treatment using different electrolytes and accelerated ageing. Further aims were to investigate if it was possible to clean silver threads using the Pleco and methods to control the spread of the electrolytes. Experiments with the Pleco were performed on a silver thread ribbon, dated 1716, attached to contemporary silk and were executed with two different types of electrolyte, one alkaline and one acidic. The materials in the silver thread ribbon were identified by X-ray fluo-rescence spectroscopy (XRF) and polarized light microscopy. Light microscopy was carried out to compare the visual differences between areas of the silver thread ribbon that were cleaned by the Pleco and areas that were not cleaned. Scanning electron microscopy (SEM) was used to examine the silver threads, the morphology of the silk and to search for degradation symptoms. Energy dis-persive X-ray spectroscopy (EDS) and attenuated total reflection- Fourier-transform infrared spec-troscopy (ATR-FTIR) were used to investigate sodium salt residues in the contemporary silk, the silk in the warp of the silver ribbon and in the core of the silver threads. The physical effects of the treatments with the selected electrolytes before and after accelerated ageing were assessed by tensile strength testing and colour measurements. This study has shown positive results indicating that local electrolytic cleaning of silver threads on silk with the Pleco containing a suitable electrolyte could be a viable option.