shoes&pattens8

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Shoes and Pałtens

water pulls the fibres together as evaporation occurs. Treatment consists of drying it by methods which leave it flexible, strong and not uniformly dark. Care has to be taken not to re-move evidence of dyes, paints and finishes. The following factors were considered when evaluat-ing which techniąues to use:

(1)    Strength and flexibility

These are important not only because they make the leather feel and look pleasant, but also because they make study and handling much easier and less likely to cause damage.

(2)    Size

Leather almost always shrinks during drying. This is not by a uniform amount but varies from piece to piece. No conservation treatment prevents all shrinkage but a well-chosen one can minimise it. It is impossible to know what size leather should be and whether the excavated size was as when buried or was either swollen or shrunken. Sizes were recorded when wet and the aim was to pre-serve these dimensions as closely as possible.

(3)    Stability

Once dry, the objects could still deteriorate. Added materials (dressings, plasticisers, backing materials, adhesives, etc) were chosen that were not liable to attack and/or decay.

(4)    Appearance

It is impossible to say what excavated leather ‘ought’ to look like. Different tanning methods, dyes and finishes give different effects of both colour and texture, and leather will darken during use. It is tempting to feel that treatments leaving it light in colour are ‘better’, perhaps because this is furthest removed from the dark, wet State, but that is subjective. Successful conservation should result in a wide rangę of colours, including black.

(5)    Presewation of evidence

Successful treatments not only preserve or re-cover size, shape, colour and feel but also any other evidence which might be present, even if not apparent to the naked eye, such as tannins, dyes and original dressings. Analytical methods are becoming morę sophisticated and even the most fragmentary and decayed piece can hołd use-ful and recoverable information.

The methods chosen (Table 21)

If it is just allowed to air-dry the shrinkage of leather is, to some extent, irreversible, as touching fibres may bond together. Two different conservation methods were used to circunwent this problem:

(1)    Soloenł drying (Rector 1975)

This method was used up to 1982. The water in the leather was replaced by another liąuid of Iow surface tension (acetone or alcohol) which was then allowed to evaporate. Although shoes treated thus were generally flexible with only moderate shrinkage, the method did have disad-vantages. First, the solvents could extract some of the remaining tannins, fats and dyes. Secondly, it could only be carried out in a work-place with adeąuate fume extraction. It was also very time-consuming. The initial Capital outlay was smali but the cost of solvents was high. For these reasons, from 1980, freeze-drying was increasingly used.

(2)    Freeze-drying (David 1981; Watson 1981) This is a gentle process. It has been in use increasingly in many laboratories in the last 12 years. Its main advantage is that there is little risk that materials will be extracted. It also puts minimal strain on delicate objects. Trials showed that the average shrinkage of the leather was less than during solvent drying (Table 22). In this method the leather is frozen and placed in a vacuum. This causes the ice formed to sublime - that is, the water is removed without going through a liąuid phase. The initial Capital outlay for freeze-drying eąuipment is high but running costs are fairly Iow and it is far less time-consuming than the solvent method. Since 1983 the Museum of London has owned a freeze-drier and most items are now dried in this manner.

Leather treated by removal of water alone can still be rather stiff and ‘thin’ and there may still be some cross-linking of fibres. To make it morę flexible, give it a ‘fuller’ feel and reduce cross-linking, a plasticiser or lubricant is added either before or after drying. This also reduces further shrinkage. Up to c.1980 a dressing was applied to all the leather after drying, consisting of lanolin and a water-repellent in either trichloroethane or white spirit (Rector 1975). This resulted in flexible leather which looked and felt ‘good’ but the pro-