Nanotechnologies for the restoration of alum-treated archaeological wood

Abstract

The project Saving Oseberg is funded by the Norwegian State with the aim to preserve the Viking Age wooden objects from the Oseberg burial mound. They were excavated in 1904 near Tønsberg, Norway, and many have been treated in the past with alum salts (KAl(SO 4 ) 2 Á12H 2 O). Alum was widely used during the early 1900s as a treatment for archaeological wood to prevent shrinkage and impart strength. In the 1990s, conservators observed an alarming condition of the objects. Initial investigations showed that the alum treatment has initiated a slow but ongoing deterioration process, attacking the wood for over 100 years. Today, the artefacts are highly acidic and have significantly reduced mechanical strength. In the last decade, the use of nonaqueous alkaline nanoparticle dispersions has provided successful results for the protection of cellulose-based materials. Alum-treated archaeological wood samples from Oseberg, with a pH B 2, have been treated with alkaline nanoparticle dispersions, and the effects of the treatment have been evaluated by thermal analysis (TG-DTG), infrared spectroscopy (ATR-FTIR) and X-ray microtomography (micro-CT) analyses. In this contribution, the preliminary results will be presented.

Selected Aspects Regarding the Restoration/Conservation of Traditional Wood and Masonry Building Materials: A Short Overview of the Last Decade Findings

“…One of the first inorganic treatments of the historical wooden elements is represented by the use of potassium aluminum sulfate dodecahydrate, developed in the middle of the XIXth century. However, its major drawbacks (among which the acid degradation of cellulose is one of the most important) led to abandoning the treatment, but not the general use of inorganic consolidants [25]. More recently, several types of inorganic materials (including nanoparticles) were applied for the consolidation of wood materials.…”

Ammonium alum in alum-treated wooden artefacts: discovery, origins and consequences

“…In any case, we might expect differences in ammonium and potassium alum reactivity to new materials being introduced in object re-treatment. Our group is developing a de-acidification method involving application of Ca(OH) 2 nanoparticles to alum-treated wood [27], during which ammonium could potentially be volatilised as ammonia gas. To gain further insight, investigations are currently being undertaken into the specific products resulting from reactions of the nanoparticles with potassium and ammonium salts present in the wood.…”

Tapping into Synchrotron and Benchtop Circular Dichroism Spectroscopy for Expanding Studies of Complex Polysaccharides and their Interactions in Anoxic Archaeological Wood

“…Over the past 20 years or so, wood artefacts such as the warships Mary Rose and Swedish Vasa have been treated with aqueous polyethylene glycol containing a broad spectrum biocide with the aim of supporting the remaining wood cell walls (a significant proportion of which is likely to be lignin due to its well documented recalcitrance to microbial and chemical decay) and inhibiting biological growth ( [46,47] and reviewed in [48,49]). Similarly, from the mid-1800's until the 1950s, concentrated solutions of alum salts (KAl(SO 4 ) 2 •12H 2 O, aluminium potassium sulphate dodecahydrate) at 90 • C were used for strengthening wooden artefacts and maintaining their shape [50][51][52][53]. The alum salt replaced the remaining water in the wood cells and recrystallized immediately upon removal from the heat treatment, thereby rapidly preserving the shape of the wooden artefacts.…”