Silver leaf and gold leaf of very pale tint, that is, which contains a large proportion of silver, should never be laid on the oil gold size, neither should metals which are subject to oxidization, as the oil has a strong affinity for oxygen, and the oxidization of the metals is set up and goes on more rapidly. If used upon a spirit size or water size, and well protected with lacquer or spirit varnish, these metals will be perfectly lasting. Their durability depends entirely on their perfect enclosure and envelopment in an air-tight case of lacquer or varnish, both under and above them.
Japanners' gold size, with, or without, the addition of a little Venice turpentine makes as good a size as can be had for metals. There are many special sizes for the purpose prepared ready for use, but nothing is better than a good full bodied japanners' size exposed to the air for a few days to fatten a little.
Aluminium leaf may be used best on a mixture of ochre ground in oil and japanners'. It is reported to be unchangeable, and is so as far as it has been tested in actual decorating. It cannot be lacquered into a good gold, but silver leaf can. Silver is more lustrous than aluminium, which has a rather leaden look when used alone. It makes a pretty combination with gold, being grayer than silver. The cheaper metals can be laid by hand, as they are so thick as to stand handling freely, and can be cut into pieces with a pair of scissors.
The principal qualification for success in gilding is a deft and delicate handling of the metals, especially gold leaf, and there must also be a ready recognition of the possibilities and peculiarities of each kind. Always remember that whatever the condition of the under size or ground, it is hermetically sealed up when the leaf is put on, which thus prevents any change or further drying in the ordinary way, so that if gold is laid on soft coats of paint, they will not all harden off together, but will go on working under the gold, expanding and contracting, and will ultimately ruin the gold leaf.