These do not require any treatment beyond protection against insects, which is attained by immersion in an alcoholic solution of corrosive sublimate, or by spraying with corrosive sublimate in either alcoholic or aqueous solution. Of course the poisonous nature of corrosive sublimate necessitates caution in its use and it should be always labelled as such.
The use of naphthalene is not always successful, and white scales of naphthalene are apt to make their appearance; nor does finely powdered pepper sprinkled on the feathers, either alone or mixed with finely powdered alum, give satisfactory results.
(r) Papyrus.
The method of cleaning and preserving papyrus in use in the Egyptian department of the Royal Museums at Berlin is as follows: Those pieces which are folded together or rolled are carefully straightened, and, if very friable, they are first placed between damp filter paper to render them uniformly pliable. Dust and dirt are removed with soft paint-brushes, crystals of salt which are often found[167] are picked off with forceps. Any growths of fungus are carefully scraped off with a knife. The papyrus thus prepared is then placed between two thick polished glass plates, the two opposing surfaces of which are covered with a very thin layer of vaseline. Air is frequently admitted to dry the papyrus, while the pressure of the glass plates tends to smooth it out, and after it has been so treated it is mounted between thin glass plates, the edges of which are pasted over with paper covered with an oil paint.
A papyrus preserved between glass plates often shows round the edges a whitish border about two millimetres in breadth, and on separation the glass plates show a slight film of the same white material on the surface which had been in contact with the papyrus. The formation of this film, which consists chiefly of common salt and is easily wiped off, may be prevented by previously washing the papyrus in distilled water, a proceeding which experience has shown to be harmless. As the papyrus will swim on the surface it should first be immersed in alcohol until soaked through; the process of steeping is then quite simple. The thinness of papyrus enables the steeping to be completed after 24 to 48 hours by two changes of the water, and care must be taken lest a too prolonged steeping should obliterate the lettering. The water assumes a yellowish or brown tint and the papyrus becomes somewhat lighter in colour on drying. Papyrus may also be preserved by zapon (see Appendix), but this method has no advantage over that of mounting between glass plates.
(s) Wood.
To preserve adequately articles of moist wood (and they are generally in this condition when first excavated), preliminary measures to prevent their drying in the air must be taken immediately after they are dug out of the earth. If found in water, as for instance articles from pile-dwellings, they should be conveyed in water; moist objects should be wrapped in several thicknesses of moist cloth, and the whole wrapped in gutta-percha membrane, or in a layer of moist moss. The cracks which arise in wooden objects which have become dried may frequently be closed up by laying them in lukewarm water.
As the earliest attempts at preservation were probably made upon wooden objects there is scarcely a collection in which a number of methods are not employed. One exception only is known to me, and here, after a plaster of Paris cast has been taken, the object is simply allowed to shrink. The methods proposed and carried out are so different and so numerous, especially as regards the liquid used for impregnation, and in such variety, that it is only necessary to deal with the most important. These may be divided into two classes, viz. dry and wet.
(1) Dry Preservation of Wood.
Moist or wet objects are placed in thin size or in a solution of isinglass till they are impregnated, after which they are dried gradually in a shady place. A solution of shellac, or varnish diluted with petroleum or benzine, is then put on with a brush.