The preservation of antiquities - Friedrich Rathgen

Zapon, the invention of Crane, of Shorthills, U.S.A., has been used for 20 years past for the protection of metals from oxidation and the action of sulphuretted hydrogen. Although the products of the various manufacturing firms differ in composition, zapon is essentially a solution of nitro-cellulose in various solvents. The nitrated cellulose, i.e. gun-cotton (pyroxyline), is generally, with the addition of camphor, dissolved in a mixture of amyl acetate (hence the peardrop-like smell) to which distillation products of petroleum, etc., are added. It comes into the market as a faintly yellow, slightly oily liquid. Its use as a preservative depends upon the fact that the evaporation of the solvent leaves behind it a fine transparent coating of gun-cotton (pyroxyline). Zapon for preservative purposes must have a neutral reaction, and must not under any circumstances redden litmus paper. Its use in this connection is due to Schill, who also recognised its suitability for other materials, as, for example, for plaster casts, the treatment of which is eminently simple, for it consists in dipping small casts, or in painting larger ones with a soft brush. It is advisable to begin at the top and apply it from above downwards, using a clean dry cloth to wipe off any excess of the fluid which collects in the deeper parts of the cast. If zapon containing about 4% of gun-cotton is used, the coating left on drying is scarcely visible; with a 5% solution a certain degree of polish results. Casts treated with zapon are less easily damaged by dust than those untreated, and may be cleaned with soap and water without injury to their surface, provided that a soft brush is used, but brushes which are stiff enough to injure the zapon coating will damage the contours of the statue. It should only be used for objects kept under cover, for rain and wide variations of temperature will attack them almost as readily as untreated casts. It can be used with equal success for antiquities of stone, clay, baked or unbaked, or for plaster after the soluble salts have been thoroughly removed by steeping, for if this has not been done the salts will soon crystallize out and loosen the protective coating. For objects which are free from salts impregnation with zapon possesses the advantage that it renders them less liable to damage from handling or dust, whilst the appearance is scarcely altered, if at all. This applies also to antiquities of metal, for unless the injurious chlorine compounds are removed by simple steeping, or reduction and subsequent steeping, treatment with zapon is useless. To bronzes, which in spite of mechanical cleaning show a somewhat unpleasant grey non-metallic appearance, zapon often imparts a distinct metallic lustre. To enhance this lustre by a second vigorous application is not recommended, for this gives the impression of a varnish. To protect articles of silver from the blackening influence of sulphuretted hydrogen, zapon is very useful, but does not afford absolute protection unless it has been thickly applied. In collections of armour much use may be found for this material. The objects are dipped and then placed in a drying oven at 105°F. [40°C.] to secure rapid drying and uniform distribution. The amyl acetate or other solvent is best conducted away, as it evaporates, into a flue or into the open, although the vapours can hardly be considered dangerous to health.

The following references will afford some information on the use of zapon in the preservation of Archives:

E. Schill, “Anleitung zur Erhaltung und Ausbesserung von Handschriften durch Zapon-Imprägnierung,” Dresden, 1899.

O. Posse, “Handschriften Konservirung,” Dresden, 1899.

G. Sello, Das Zapon in der Archivpraxis (“Korrespondenzblatt des Gesamtvereins der deutschen Geschichts- und Alterthumsvereine,” L., 1902, p. 195).

Schoengen, Over hat Zapon (“Nederl. Archivenblad,” 1902, 1903, Nos. 1 and 3).

J. Perl, Das Archiv-Zapon (“Korrespondenzblatt,” LII. , 1904, pp. 119 and 435).

G. Sello, Die bei der Zaponverwendung in der Archivpraxis gemachten Erfahrungen (“Korrespondenzblatt,” LII. , 1904, p. 439).