A lot of the style of gilding will depend on both the date of manufacture and the method used to appy gilding.
You have the traditional mercury fire gilding, done by evaporating gold 'dissolved' in a mercury amalgum 'butter' which creates a thick gold bonded to the surface, often 8 to 20 microns thick. Typically this can be identified with a very matt finish and a distict border appearance to the rear that was not coated. Fire gilding is usually in the 18 to 23.5 carat range.
Most gold electroplated up to the 1960's or 70's was usually a 'soft' gold. Basically a carat alloy of one form or another without any trace elements to increase the surface hardness. Usually this was done without the use of a nickel underplate and was often in the range of 3 to 8 microns.
With advances in chemistry from the 60's onwards, various trace elements were added to the gold alloy plates, such as nickel, iron and cobalt, in the 0.1% range, increasing the surface hardness and wear resistance by around 3 fold. (from 60-80 HV to 200-240 HV)
Additionally grain refiners and other chemicals allowed the creation of bright golds and with nickel underplates along with the increasing cost of gold, thicknesses were reduced to around 0.2 to 2 microns range on average.
Matt gold electroplating is still possible, though these are soft 24k primarily for the electronics industry.
Modern buttons are usually now done in bright gold with a heavy matt laquer which is subsequently selectively removed to give the appearance of burnishing.
Hopefully the link below will work, and shows the refurbishment of postillion buttons for the Royal Household and the burnishing method that was traditionally done of fire gilded items.
[URL="https://www.facebook.com/162795927083995/videos/684641111992816/?eid=ARBQip-SvXIRb-2CzYDq1yfFuvHwvxdmW3RSgR2D8jQbdGX_0oRyjr5kQEpRqO6Y Bq01PJZFTaJvwSqT"/URL]
|