Can't say that I can find an answer to your particular button, though did find some information on the Double Gilt
THE 19TH CENTURY brought a more practical sensibility to the world, and with it, new kinds of buttons.
The French Revolution had swept away much of the extravagance of the aristocracy, and the dandies who had once so cravenly imitated the gaudy French kings now adopted the characteristic dark blue coat of Beau Brummel, with its large brass buttons. Women's neoclassical fashions required no buttons.
Buttons became smaller, usually about half the size of 18th century buttons. And, while they might still be handcrafted works of art, more often now they were mass-produced works of craft. France was slow to mechanize, so ingenious England gradually became the world's premier buttonmaker. And, created the first real button sensation of the new century.
The first wonderfully sparkly gilt buttons were made in Birmingham between 1797 and 1800. They were elegant, yet affordable. People took to them immediately, and they became the height of fashion. Even the Americans began making gilt buttons by 1810, after stealing the gilding secret from the British!
Actually, the process was a fairly simple one. Five grains of gold per gross (144) of buttons was added to a mixture of mercury, then brushed on the brass buttons, which were then cooked in a furnace. Buttons could be double gilt, triple gilt, and so on, depending on the number of grains or number of brushings used.
The new gilt buttons were the vanguard of a "golden age" of metal buttonmaking that flourished in the first half of the 19th century, and produced buttons that haven't been equaled to this day. Sporting buttons for the gent, military buttons for the soldier, even livery buttons for the household servant were all beautifully crafted.
G8r4evr