Dictionarium polygraphicum. To japan brass...

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol II.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
To japan brass, such as is us'd to gild brass buttons, or make them look like gold.

This may be us'd upon leaf-gold, or upon what is called the German leaf-gold, or upon brass, or upon Bath metal, which, are design'd to imitate gold.

Take a pint of spirit os wine, and put it into a retort-glass, then add a quarter of an ounce of gamboge, half an ounce of lake, and half an ounce of gum-mastick; let this in a sand-heat for 6 days, or near the fire, or put the body of the retort frequently in warm water, shaking it twice or thrice a day; then let it over a pan of warm small-coal dust; and having first well-clean'd the metal, do it over thinly with this varnish, and it will appear of the colour of gold; it may be dried in a de clining oven, and it will not rub off.

N. B. This is a gcod varnish to mix with any colours that incline to red, and the white varnish to mix with those colours, that are pale, or of any other sort.