Join Date: Nov 2013
For the most part the gilding is contained roughly within engraved lines but in some areas , such as the top of the flashpan cover it isn't. It appears the amalgam was simply painted onto the steel with a brush to enhance , rather than simply to fill in the engraved design. Where engraving is present within a gilded area the gilding is only on the flat surface , and does not fill the engraved lines.
The Royal Armouries research department claims to have found traces of copper as well as mercury in fire gilding as applied to blued armour and suggests that a wash of copper ( malachite ? ) may have been applied to help the mercury gold amalgam to adhere. Because the mercury volatises at a relatively low temperature the precipitation of the gold and the colour treatment of the steel can occur at a similar temperature. Obviously , as you know the quality of the blue depends on the carbon content of the steel so we can assume the lockplate has previously been case hardened.