Insects can also be killed by naphthalene vapour, but as naphthalene is insufficiently volatile at ordinary temperatures, the method above described is more convenient[173].
Preservation and Cleaning of Coloured Wooden Objects.
For objects of this kind materials should not be used which, like varnish, tend to darken and so to damage the colours. Gum-dammar solution (page [70]) answers the purpose, but colourless collodion is better. Colours which are soluble in water (as is frequently the case with wooden objects from Egypt) cannot of course be cleaned with water, but benzine may be applied by means of soft cloths or brushes. Resinous or pitch-like substances may often be removed from coloured objects by turpentine mixed with benzine or ether.
A method of cleaning gilded or brightly coloured ecclesiastical figures which is used in the Breslau Museum is the application of a mixture of copaiba balsam and ammonia. This method is similar to that used to clean paintings[174], the action of the solution being that of a mild soap.
Antiquities which were originally uncoloured, but which have been subsequently painted, may be cleared of paint by means of a solution of caustic soda in water or alcohol.
(t) Amber.
After the mechanical removal of any adherent earth and dust, the specimen should be rubbed carefully backwards and forwards between the fingers covered with a soft woollen glove. Particles of soil should be picked out of any holes and indentations by using a strong horse hair[175]. It is then preserved by impregnation with a solution of shellac, poppy-seed oil, or isinglass (pp. [70] and [86]).
The following particulars of the method used in Messrs Stantien and Becker’s collection of amber have been supplied by Prof. Klebs:
“Amber is preserved best in distilled water: I add a very small quantity of glycerine and a still smaller amount of alcohol. A proportion of alcohol greater than 1% is injurious to the amber. A thick layer of gelatine containing glycerine is an excellent medium for the preservation of large objects if they are kept free from dust. This layer should be washed off and renewed every few years.”