In addition to the protection from dust afforded by closed glass cases, it is also important to protect objects from the action of direct sunlight, especially during the summer months. There is, for instance, no doubt that the decay of bronzes, even of those with a patina which is apparently sound, is hastened by the great variations of temperature, caused by the rays of the sun falling directly upon them. Similarly objects which have been preserved by the application of solutions of resin or varnish should be protected from the direct access of sunlight, for the sudden warming may easily cause cracks. Nor should antiquities be kept near the heating apparatus. There is another precaution, to which too little attention has been paid, viz. the protection of objects as far as possible from even diffused daylight. Although no investigations upon the extent of the injurious action of light have as yet been published, light is not without influence upon the outward appearance, and therefore also upon the material condition of antiquities of organic origin. But even inorganic objects, such as pigments, glass, enamel, amber, etc., are affected by light; it is therefore certainly advisable to protect antiquities of all kinds from light during the time in which they are not exhibited to the public.
The public is effectually prevented from fingering antiquities which are enclosed in glass cases, but it may be well to remind those who have to handle them in the course of their duties that contact with the bare hand can only be harmful, even though fingering is understood to be beneficial to modern bronzes by inducing the formation of patina. The bright surface of metallic iron which results from treatment by Blell’s or by Krefting’s method, especially if there is a thin coating of paraffin, should not be touched at all with the bare hand, but only with a cloth or a glove. Bronzes, whether intact or restored, and iron objects, should never be in direct contact with those which show efflorescences.
The usual custom is to attach labels of painted cardboard or metal by means of thin metal wire. The tendency to rust makes iron wire unsuitable, especially for objects containing salt, which are quickly affected; thus light coloured earthenware may soon be covered with spots of rust. Copper wire and nickel wire are liable to be similarly attacked. Many years ago it was noticed[176] in the Ethnological Museum at Berlin that nickel wire when in contact with silver objects which were covered with silver chloride was destroyed by the formation of a deliquescent green nickel salt. Silver or platinum wire forms the most suitable means of attachment, but if the expense of these is too great, copper or nickel wire may be used, except in the cases mentioned above.
Small objects of any kind, which one still frequently finds kept in open cases, are better preserved in upright glass cylinders with glass stoppers, or in cheaper glass tubes, one end of which is fused and the other closed with a cork.
Conclusion.
The methods of preservation which have been described in the preceding pages may be thus tabulated and summarised:
| Methods. | Application. |
| Steeping in water, drying and impregnation. | Limestone, Earthenware, Iron, much corroded. |
| Direct impregnation. |
(1) Unbaked earthenware, etc., (2) Bronze objects with little or no metallic core, or showing a cracked or warty surface, (3) Objects of wood and of other organic substances. |
| Removal of compounds of oxygen or chlorine | |
| (a) by chemical process, | Iron objects in a good metallic condition, |
| (b) by electrolytic process. |
(1) Iron objects with a sound metallic core, (2) Bronze objects with a sound metallic core. |
| Mounted thoroughly dry and hermetically sealed. | Valuable bronzes in an advanced state of decomposition. |
There will be no difficulty in the choice of methods for limestone or earthenware, whether kiln-dried or sun-dried, for a simple experiment will prove whether steeping is likely to cause injury or disintegration.
The methods are themselves simple and inexpensive. For organic substances the chief question is the choice of the most suitable medium for impregnation.
Iron and bronze present some difficulty, although the use of a file will readily show whether reduction is feasible.