ip-coating and a clear alkaline glaze.
Perhaps it was that at this period tin was almost as costly as gold, and
it was only when potters with an oriental training brought their skill
to Spain, where tin abounded, that the relative cheapness of the
material led them to employ it, so far as is known, exclusively. (There
is a wide distinction between the tin-enamelled and the slip-faced
wares, glazed with an alkaline glaze. In the latter, the more oriental
type, the slip-coating is of fine white clay and sand, and this is
finished with a transparent alkaline glaze containing little or no lead:
in the former there is no need of a coating of slip, for the addition
of oxide of tin to a glaze rich in lead gives a dense coating of white
enamel, opaque enough to disguise the color of the clay beneath.) Such
colours as were used for painted patterns were painted over this enamel
coating before it was fired, so that they became perfectly incorporated
with it, and then this ground furnished a splendid medium for the
development of those thin iridescent metallic films that we call
"lustres." The knowledge of this lustre process had been brought from
the East also, where it was used on another ground, and with the growing
use of lustre pigments containing copper as well as silver--until the
red, strongly metallic copper lustre almost ousted the quieter silver
lustres--we get the simple technique of one of the most distinctive
kinds of pottery known.

[Illustration: FIG. 43.--Hispano-Moorish Plate, painted in blue and
copper lustre.]

Briefly, the wares were "thrown" upon the wheel or "pressed" on modelled
forms--handles, ribs and dots of clay, or strongly incised patterns were
often added by hand--and they were then fired a first time. A coating of
the tin-enamel (rich in lead as well as tin) was applied, and on this
coating designs were painted in cobalt and manganese; sometimes these
colours were only used as masses to break up the background. Then the
second firing took place and the piece came from the firing all shining
and white, except where the blue or brownish purple had been painted
(see fig. 43). The lustre pigments, a mixture of sulphide of copper or
sulphide of silver, or both with red ochre or other earth, was then
painted over the glazed surface with vinegar as a medium. The repainted
piece was fired a third time to a dull red heat, and smoked with the
smoke from the wood used in firing, and when cold the loosely adhe