Towards quantified assessment of aqueous chloride extraction methods for archaeological iron: De‐oxygenated treatment environments

Watkinson, David; Al-Zahrani, A.E.S.

doi:10.1080/01410096.2008.9995234

Cited by 17 publications

(22 citation statements)

References 28 publications

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“…The relatively small sample sizes of the few studies providing quantitative extraction data (Watkinson, 1982(Watkinson, , 1983(Watkinson, , 1996Watkinson & AlZahrani, 2008) make statistical evaluation difficult. In the most recent study (Al-Zahrani, 1999;Watkinson & Al-Zahrani, 2008), the alkaline deoxygenated treatments extracted an average of 97-99% of the chloride ions present in objects. Such high extraction efficiencies have been questioned, as the potential exists for loss of chloride ions as HCl during the digestion phase of the experimental work (Scott & Eggert, 2009, p. 141;Schmutzler & Eggert, 2010).…”

Section: Introductionmentioning

confidence: 99%

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

Rimmer

Watkinson

Wang

2012

Studies in Conservation

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Chloride-contaminated archaeological iron is unstable and problematic to store and display within museum collections. Reducing its chloride ion content using aqueous desalination followed by storage in controlled relative humidity offers one treatment option. This study reports a quantitative assessment of chloride extraction by aqueous deoxygenated alkaline desalination solutions from 120 individual archaeological iron nails. The three treatment methods comprised alkaline sulphite solution (0.1 M NaOH/0.05 M Na 2 SO 3 ) at room temperature and at 60°C and sodium hydroxide solution (0.1 M) deoxygenated using a nitrogen gas positive pressure system at room temperature. Chloride extraction was monitored using a specific ion meter. The nails were digested after treatment to measure their residual chloride content. A wide range of extraction patterns emerged, with the majority of individual treatments extracting 60-99% of the chloride present. Residual chloride levels for 87% of the objects fell below 1000 ppm and 42% were below 200 ppm. Although no treatment extracted 100% of the chloride in the object, alkaline desalination produced very significant reductions in chloride content. The impact of this on future corrosion of the objects is discussed. This quantitative and statistically viable assessment of deoxygenated desalination treatments provides evidence to support their use in conservation practice, which will impact on procedures for the preservation and management of archaeological heritage.

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Section: Introductionmentioning

confidence: 99%

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

Rimmer

Watkinson

Wang

2012

Studies in Conservation

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“…Generally, the oxidized layer and the marine encrustation associated with chloride compounds were on the surface of the marine iron artifacts. The state of the object is related to earlier work of Watkinson and Al-Zahrani (2008) found chlorides can also be associated with solid corrosion products. Following excavation reaction of iron with atmospheric oxygen and moisture which readily forms β-FeOOH (akaganeite) in low pH and Fe 2+ / Cl -rich environment, formed at the metal surface when iron dries out (Watkinson and Al-Zahrani 2008).…”

Section: %mentioning

confidence: 99%

“…Sodium hydroxide or/and plasma reduction efficiently to decrease the chloride level and improves their color and shape by formation of magnetite. Watkinson and Al-Zahrani (2008) resulted that aerated treatment environments extract less chloride than de-aerated systems and have erratic treatment efficiencies, whereas de-oxygenated wash environments aid the removal of chloride from archaeological iron. The best chloride extraction efficiencies are obtained when the wash solution is both alkaline and de-aerated.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…However, this is obviously not possible for objects in a museum collection. Since sodium sulphite in the alkaline sulphite solution acts as an oxygen scavenger rather than a reducing agent, recent research carried out by Watkinson and Al-Zahrani (2008) suggests that deaerated sodium hydroxide could be a more effective desalination solution than alkaline sulphite (Wang and others 2010).…”

Section: Sodium Hydroxide and Sodium Sulfatementioning

confidence: 99%

“…Average extraction efficiencies for deoxygenated NaOH solution were similar, irrespective of whether air was excluded by the oxygen scavenger Na 2 SO 3 or by nitrogen gas. Consequently the use of nitrogen gas is preferred, as it does not introduce SO 3 and SO 4 ions into the object (Watkinson and Al-Zahrani 2008).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

See 2 more Smart Citations

Conservation methods of iron artifacts recovered from the marine environment

Ahmed¹

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The efficiency of electrochemical methods for the removal of chloride ions from iron marine archaeological objects: A comparative study

Coelho

Oliveira

Carvalho

et al. 2012

Materials & Corrosion

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The conservation of archaeological marine iron artefacts requires chloride ions removal. In this study, the removal of chloride ions was undertaken by two electrochemical methods: the electrolytic and the galvanic reduction in alkaline media. The results were compared with those obtained by the washing and the sulphite reduction methods, under identical conditions. The experiments were performed on samples coming from an 18th century cast iron cannon‐ball, found in the archaeological context of a shipwreck, l'Océan, which sank near the southern Portuguese coast, in 1759. The extraction of chloride ions was monitored by ionic chromatography (IC). The results allow to conclude that the sulphite reduction experiments using the mixture 0.5 M NaOH/0.5 M Na2SO3 presents the higher efficiency in the first week, being further overcome by both electrochemical methods. After 40 days of treatment, the electrolytic reduction is the most efficient method.

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Towards quantified assessment of aqueous chloride extraction methods for archaeological iron: De‐oxygenated treatment environments

Cited by 17 publications

References 28 publications

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

Conservation methods of iron artifacts recovered from the marine environment

The efficiency of electrochemical methods for the removal of chloride ions from iron marine archaeological objects: A comparative study

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