In the case of coloured terra-cotta care should be taken to ascertain whether the colours are likely to suffer during steeping. There is no danger of injury if the steeping is not too prolonged; in fact, the removal of the dust during the procedure often brings out the colours more clearly. If the Egyptian ostraca (clay fragments with black script) require to be washed they should be carefully watched in order to preserve the script, and therefore should be placed in the bath in such a way that the lettering is visible.
These fragments are usually curved and bear the script upon the convex side, care should therefore be taken that they are completely immersed, and that no large air-bubbles prevent the access of the water to any part of the under-surface. The writing is done with either lamp-black or more rarely some form of iron ink, and is retained mechanically by the porous character of the ostraca. In the latter case the characters may be enhanced by the application of a dilute solution of tannic acid, which sometimes proves useful also for limestone pieces.
If these fragments are sufficiently few in number to allow each to be put into a separate glass vessel, the washing out of the salts is completed so quickly that there need be little danger of obscuring the script. When large numbers were to be washed and when the script was already indistinct I have employed the following method: After examination as to their fitness for immersion the fragments are placed on a wooden grating in a tub, in which they remain for a couple of days, during which the water is renewed once. They are then taken out and allowed to dry. All those which still show the script distinctly are separated and their steeping is completed, but the remainder, having been completely dried, perhaps on the top of a warm stove, are brushed over once or twice with a dilute (1:6) mixture of varnish and benzine in such a way that the surface is only moistened, and when dry shows no gloss. The pieces thus superficially varnished are kept in a dry place for about two months, until the varnish is hardened; the process of washing out the salt is then begun again. The thin coat of varnish fixes the script without interfering with the steeping. The varnish solution must be dilute, for a thick coating will partially peel off from the object in the course of the steeping, or will remain in the pores in the form of opaque particles, and thus render the script illegible.