CCI2014050713

-18-

Th< i conseryation treatment

The pieces of the leather jerkin were rinsed with tap water and as much dirt as possible was removed from it by hand.

Immersion of the soaked obj ect in a dilute Pakite solution

Oakite is a commercial product consisting of orthophos-phoric acid and corrosion inhibitor. We diluted 400ml of oakite with 100ml of tap water. Oakite was originally developed for cleaning rusty objects. It can be replaced by a solution of 3% orthophosphoric acid, oxalic, or ascorbic acid containing three drops of neutral soap, to get a better penetration. The main purpose of this treatment was to dissolve the iron salts formed mainly between tanning materials (tannins) and iron, which give the leather a dark colour. Another aim was to dissolve the water insoluble carbonates and bicarbonates, which make the leather stiff. The treatment took about 1 hour and simply consisted of soaking the obj ect and tuming it over from time to time. The acid solution used in the previous step was then washed out with running tap-water. This procedurę took about 3 hours.

After 2 hours, 40ml of concentrated ammonium hydroxide were added to the leather to neutralize the residual acid.

The tap was then tumed off and the obj ect was allowed to stand for 30 minutes. Finally the ammonium salts were washed out under the tap over 30 minutes.

The pH was then measured both on the water and on the leather. The pH of the leather was still below 3,0. The last two 30 minutes treatments were therefore repeated.

Also a measurement of the conductivity of the solution was performed to find out if all the salts were washed out.

The bulk of adhering water was removed from the outside and the inside of the soaked pieces of leather with tissue paper which was then also used as an absorbent wadding inside the obj ect and for extemal wrapping.

The object was next brushed over liberally with castor oil, which penetrated the leather and drove the water to the inside where it was absorbed by the paper wadding.

The appication of oil was repeated five times at four hours intervalls. The paper wadding was replaced by a new batch of dry paper several times until all the moisture had been removed and only óil was present in the leather. The temperaturę in the room where the work w.m done was maintained at 1 4°C to prevent the moisture from evaporating too fast. A smali sample of the object was used to deter-mine the fat content of the leather, both free fat and bound fat, the pH of the leather and the iron and copper content before the treatment and after the treatment.

The free fat content, determined by means of a soxhlet extraction with petroleum-ether was rather Iow: 0,8%.

The percentage of bound fat was determined by means of a destruction method which proceeds as follcws: a sample of leather, size about 1cm² is treated with a few drops of a ooncentrated solution of sodiumhydroxide, 25% in strength. The leather is hydrolised canpletely and goes into solution, until there are no morę fibres present.

All the fats in the leather are converted to soaps, water soluble both bound fats and free fats.

The dark brcwn coloured solution is neutralised by means of a few drops of concentrated acid, for instance nitric acid, until the pH of the solution is 7,0.

Now all the soaps are converted back to fats which are not water soluble anymore.

After this treatment a few millilitres of organie solvent for instance petroleum-ether or hexane are added to the solution. The glass is closed with a stopper and vigorously shaken for a few minutes with intervalls.

The fats go into solution in the organie solvent and when the layers of water and organie solvent are separated in a two layer system, with on top the organie solvent it is possible to separate the two layers.

After evaporisation of the solvent there will be a residue of fat and the percentage of total fat can be determined.

In this case total fat was 1 ,7%. Free fat content was 0,8% so percentage of bound fat was 0,9%.

This are both very Iow percentages and in this case fat must be added until a total of 5%.

After the treatment of the object again free and bound fat were determined and now the percentages were for total fat: 5,4% for free fat: 4,4% resulting in a percentage of 1,0% for bound fat. The generał oonclusion is that there is no inerease in the percentage of fat bound to the fibres but the added amount of fat is present as free fat.

We have to look deeper into this by means of a research programme comparing different types of fats and oils in order to find out if there are differences in behaviour.