It is covered with scrolls of gilded copper on blue champleve enamel.

In a process known as champleve, she uses acid to eat out pockets in the metal and then fills them with enamels.

And very much worth the examining is the use of enamels, embedded as champleve or painted on metal, which now create fragile shadows, almost ephemeral.

The champleve enameled plaques by Ms. Schwed's daughter, Katharine S. Wood, are also esoteric.

But exceptional examples are uncommon in today's auctions, which is why Sotheby's sale is unusual: there are, in all, seven lots of 12th- and 13th-century champleve enamels.

The Twelve Apostles, in brilliant blue and green champleve enamel, are separated by a kind of intricate copper engraving done in a circular pattern known as vermicule (wormlike).

It was made in Limoges around 1225 using the champleve technique, in which a design is chiseled into bronze or copper, filled with glass and minerals, and then heated until they fuse into brightly colored enamels.

A practising coppersmith, who was also engaged in manufacturing fine champleve enamel work, is certainly known from Catterick, where the bottom of a wooden waste tub was found intact, full of small filings and chippings and some tiny fragments of coloured enamels.

Uppermost was a large and exceptionally elaborate three-hooked hanging bowl of Insular production, with champleve enamel and millefiori mounts showing fine-line spiral ornament and red cross motifs and with an enamelled metal fish mounted to swivel on a pin within the bowl.

Among the methods by which other artists have added color to metal components are enameling (both cloissone and champleve), oxidizing copper to achieve a wide range of color, taking niobium to brilliant tones by electrochemical treatment, adding on colored telephone wire and other plastic materials and tinting woods.

LEAD: A Medieval Rarity A Medieval Rarity An unrecorded 12th-century enamel plaque depicting Cain and Abel - the only one of 12 surviving Mosan champleve images in private hands - is stirring excitement in London, where it is to be auctioned next Thursday.