JACOBI'S METHOD. The method of preservation of iron antiquities used in the Saalburg Museum at Homburg is described by Jacobi as follows: The object is heated in the fire of a forge, which causes the chief part of the rust to flake off, while any rust which still adheres is removed when cold by water and brushing. The object is again held in the flame with tongs and heated (smaller objects may be placed on an iron plate); and during the heating is quickly taken out three or four times and each time brushed over with linseed oil. Most of the linseed oil is thus burnt and the deposition of carbon gives to the iron a black colour, while the oil which has been partially burnt or hardened by the heat produces a slight lustre. This process, as carried out at Homburg by a locksmith, is that which blacksmiths ordinarily use to blacken iron objects and to protect them from rust. The preservation has proved permanent, and only in rare cases has it been found necessary to repeat the process. These good results are probably due to the fact that the antiquities of iron preserved in that Museum are for the most part found in good condition, having very little rust and certainly containing only a very small amount of chlorine. Iron articles which contain chlorine but which still have a good metal core, after washing, drying, and a cautious preliminary application of heat, are ready for treatment by Jacobi's method.
INLAID IRON OBJECTS require especially cautious treatment. Although I have not had any personal experience in the treatment of objects of this kind, good results have been obtained in several Museums, especially in that at Mainz.
The following quotation from the "Merkbuch" (p. 75) describes the method which is applied at Mainz, where it probably originated:
"Objects of this kind which are likely to have been originally inlaid with silver, gold, copper or brass, as is frequently the case with objects of the Merovingian period, are not placed in alcohol after the steeping, but are warmed and dipped three or four times into a hot dilute solution of isinglass. The heating is necessary, otherwise the isinglass will set on the surface and will not penetrate into the interior. When the object has been dried and the isinglass has set, the layer of rust which covers the inlaid ornaments is scraped off with a graving tool, and any spongy hollow parts are filled up with a paste made of iron rust and isinglass, before the inlaid work is cleaned. During the scraping the object is held in the left hand on a little wooden board covered with plush or thick chamois leather, to which it is fixed as firmly as is necessary by means of a vice. In scraping special care must be taken that the graving tool follows the lines of the designs, for in scraping across the design it may slip under the flat silver thread and raise it out of its place. When the ornamentation has been completely laid bare, it is rubbed with emery cloth and then polished with a brush and fine emery powder. The piece is then dipped into a solution of gum-dammar, and, when the surface is dry, emery is again used to remove the varnish, which gives the silver a slightly yellow colour. The object is then protected from the influence of air and moisture by the transparent retouching varnish of Sohnée frères (Paris)."