to the promotion of the art. From his
experiments were discovered the principal colours to be used for
enamelling, and the means of vitrifying them. Rubens painted his portrait;
certainly one of the finest now extant. It originally ornamented the
Arundel collection: was then at Dr Mead's, Lord Besborough's, and is now
(1826) at Cleveland House.'... A monarch who was so fond of painting as
Charles I., was fortunate in having the assistance of a person who
combined a love of art with a scientific knowledge applicable to its
mechanical operations. It is not surprising that such an amateur as De
Mayerne should enjoy the confidence of the first painters of his time; or
that in return for the useful hints which he was sometimes enabled to give
them, they should freely open to him the results of their practical
knowledge. Such communications, registered at the time by an intelligent
observer, threw considerable light on the state of painting at one of its
most brilliant periods, and tend especially to illustrate the habits of
the Flemish and Dutch schools."

De Mayerne records the use of sand in purifying oils, as a communication
from Mytens, painter to Charles I., _before the arrival of Vandyke_.
"Coming from such a source," says Mr Eastlake, "it may be classed among
the processes which were familiar to the Flemish and Dutch painters."

The works of the Flemish and Dutch painters are undoubtedly those which
the artists of the present day would desire to be the tests of vehicles
and of colours. They can scarcely have, therefore, a more valuable
document than this manuscript of De Mayerne, the friend of Vandyke. From
this source there is much information with regard to colours. It has
always been supposed that Rubens in particular was lavish in the use of
Naples yellow. It was largely used by the Italian painters; but it is
omitted in the list of colours of the Dutch and Flemish. Many yellows,
which in oil alone will not stand, are, it seems, durable if protected by
an oleo-resinous medium. After enumerating many other yellows, Mr Eastlake
remarks--"There was, however, one substance, viz. gamboge, now
undeservedly fallen into disuse in oil painting, which is superior to
most, if not to all, of those above named; the colouring matter united
with its resinous portion, which renders it more durable in oil painting,
may be easily freed from mere gum. De Mayerne, it would seem on good
grounds, pronounces in its favour; and his spec