NINMACH 2017

Quantitative chlorine analysis of archaeological iron objects by PGA Analysis

12 Oct 2017, 12:45

20m

Felolvasóterem (Hungarian Academy of Sciences)

Oral presentation Prompt gamma activation analysis PGAA & NAA

Speaker

Dr Britta Schmutzler (State Academy of Art and Design Stutttgart)

Description

**Background** Archaeological iron objects usually suffer from post excavation corrosion, induced by chlorine, which diffuses into iron objects during burial. Objects conservation has the task to extract the chlorine by e.g. washing methods since the destruction of this corrosion form is drastic and hard to control by climate conditions. Several approaches were developed the last decades, but "Alkaline Sulphite Method" has become to an international standard method in conservation for archaeological or marine objects. It is based onto alkaline washing solutions of half molar sodium hydroxide, which contain half molar sodium sulphite for deaerating the aqueous solutions, heated up to 70 °C and stirred. Several variations of this protocol were examined by conservation science the last years due to restrictions in time, budget and personnel in the conservation departments, creating needs for simpler and cheaper possibilities in mass treatment. For example, diluted or cold solutions were tested in the empirical research project "Saving from Rust" (funded by DBU Deutsche Bundesstiftung Umwelt/ Osnabrück/ Germany), using original archaeological material as specimens. The key for meaningful results is the chlorine resp. chloride analysis, which could formerly be conducted with destructive methods only. So there was the need for non-destructive methods for chlorine analysis in further projects what could be realized by PGA analysis at the Heinz Maier-Leibnitz Zentrum (MLZ). The residual chlorine, which is still present inside the treated objects after conservation, is the hard criterion in the evaluation of the conservation success – the less, the better. **PGAA in the framework of conservation research** The research project "Besonderes Eise(r)n bewahren" (DBU funded) is presented with data from chlorine analysis by PGAA, complementary checked by oxygen consumption as a second non-destructive testing for corrosion by residual chloride (the more chlorine a treated object contains, the more oxygen is consumed in accelerated corrosion tests). The conservation treatment was conducted by use of alkaline solutions with varying physical parameters (e.g. temperature; ultrasonic assisted extraction). PGAA data were used for comparison of the impact of these different treatment parameters. The huge advantage is the possibility of repeated measurements before, during and after treatment as well as control measuring (reproduction). The main goal of the research work is to diminish the residual chlorine to very low or zero level for optimum stabilization of the archaeological iron objects against post treatment corrosion. And to preserve as much as archaeological iron objects in their actual state of condition for upcoming research approaches.