Acidity Measurements on the Victory Sail

In the absence of active biological attack, the two dominant processes leading to natural deterioration of cellulose are acid-promoted hydrolysis and oxidation. The latter is quite slow, and we would expect cellulosic artefacts that are above neutrality and kept in a stable environment to remain in relatively good condition for hundreds of years. However, those that are somewhat acidic can show significant signs of deterioration within a few decades. 

As we have indicated above, the ageing of fibres like flax often results in the formation of acidic degradation products. These, together with adsorbed acidic atmospheric pollutants, can continue to promote further damage through the hydrolytic depolymerisation of cellulose. So, in relation to its stability, it seemed important to estimate the acid content of the Victory sailcloth. There are two approaches that can be taken surface measurements on the fabric and acid extractions. 

We recorded the surface pH by pressing a moistened non-bleeding indicator paper to the fabric for a short period, after which the resultant colour change was interpreted. These revealed pH values between 3.3 and 4.0 in the various locations tested, whereas for new linen sailcloth the value was around 6.0. While it is difficult to deduce the true acid content from this type of assessment, nevertheless values below pH 4 are generally regarded as a cause for some concern over the longer term, leading to recommendations for remedial action. 

Yarns from the modern, unaged sailcloth had a small acid content, probably just reflecting residual weak acid constituents of the plant fibres, such as 

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