Science and Heritage Programme

Interventive conservation of black-dyed organic materials – the problem of metal-polyphenol complexes

University of Manchester/ The British Museum 

Award holder - Professor Christopher Carr
Student - Helen Wilson


The project endeavours to develop novel chemical stabilisation treatments to address the problems presented by organic materials suffering from severe metal-catalysed degradation due to the presence of black metal-polyphenol dyes (where the metal is iron or mixtures of iron and copper or iron and other metals). Such materials are widespread in any museum containing ethnographic and/or textile collections, their preservation presents a major challenge and deterioration can lead to the total loss of affected areas. Interventive conservation treatments which could effectively halt the autocatalytic deterioration must arrest the metal ion redox cycle. This could be achieved through the chelation of the metal ions in a stable complex or through various antioxidant mechanisms which act as peroxide decomposers, radical scavengers or oxidative chain breakers. Additional potentially beneficial treatments include the deacidification and consolidation of the substrate material. This research project will focus on the evaluation of a variety of non-aqueous chemical stabilisation treatments building on experience gained from related studies in the areas of heritage science and from the medical,food and textiles industries. If appropriate, as part of the project it is intended to apply and assess the newly developed method(s) on selected museum objects.


Which chemical stabilisation treatments could effectively halt the rapid deterioration of black-dyed organic materials?


All experimental work will be carried out on model materials dyed according to historic recipes. The models will be subjected to a minimum of two accelerated ageing regimens. Experimental studies of stabilisation treatments include deacidification methods, chelation methods and the application of antioxidants. The treated model materials will be subjected to further accelerated ageing and tested to monitor the effectiveness of the treatments using both mechanical and chemical methods.


The project is anticipated to lead to improvements in conservation practice of metal-polyphenol dyed materials and further the understanding of the deterioration and preservation of these fragile materials.
The results will be disseminated widely, thus enabling important cultural material not only to survive but to be made accessible in a manner that might not otherwise be possible.


Professor Chris Carr (University of Manchester); Dr Marei Hacke (British Museum)


Helen Wilson

Helen Wilson studied for an MSc in Chemistry at the University of Oxford. In her final year she collaborated with paper conservator Ally Greathead at the Ashmolean Museum to produce a thesis entitled ‘Analysis of the current research into the chemistry of iron gall ink and its implications for paper conservation’. Helen’s growing interest in conservation science  developed further during a one year ICON HLF internship at the Pigmentum Project. In 2008, she started her PhD project, which is now in the second of three years.

Iron-tannate complexes (metal-polyphenol molecular complexes) are the key colouring agents in iron-tannate dyes and iron-gall inks which are present on many museum objects world-wide. The complexes are formed through the combination of iron ions and tannic acids and there is often an excess of iron in the dye or ink which arises from the formulation composition and/or breakdown of the iron-tannate complex. This iron excess catalyses oxidation and acid hydrolysis degredation of the coloured substrate, severely decreasing the object’s lifetime. 

Ancient Egyptian basketry, Maori piu piu (skirts), African masks, Japanese Hina dolls and Apatani rain capes are just some of the objects in the British Museum’s collections which show signs of accelerated degradation due to iron-tannate dyes. These objects are often very delicate, may be 3D in nature and may be made of composite materials of which only some are iron-tannate dyed. This makes available aqueous treatments designed to limit the iron-catalysed degradation unsuitable. This PhD aims to develop a non-aqueous treatment for such objects to inhibit the degradation caused by iron-tannate dyes. 

Model iron-tannate dyed textiles of cotton, abaca, wool and silk have been produced following collections research, literature research, and experimentation. An accelerated ageing regime has been designed to include pre- and final ageing stages. The model dyed and undyed textiles will be pre-aged before the application of a range of treatments such as radical scavengers, metal-ion chelators and deacidifiers in non-aqueous solvents. To assess the long term impact of the treatments, a final ageing stage will be included. The samples will be characterised using a range of analytical and chemical techniques including electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), size-exclusion chromatography (SEC), spectrophotometry, pH testing, and tensile testing to establish the effectiveness of the treatments.

Image: Helen Wilson in front of a Winch dyeing machine whilst silk dyeing is in progress. Image © Philippa Duffus.


African cloth

Image: African Kuba cloth (unregistered). Image (c) Helen Wilson