To me it looks like damascene work. I think that's the right word,,hope it's spelled OK..
Done by roughing up the steel surface and then hammering and/or burnishing the gold down onto it.
Details in the gold added at that time. Then blued (fire or charcoal blued)
The 'rough-up' is extremely fine on the best work. Done from 3 directions it creates teeth to impale the soft gold onto. The gold can be wire,,they call it 'thread' in damascene work,,and is of diameters most engravers wouldn't think of using for inlay work. Just a few .000" in diameter in some cases for line and detail work.
Larger areas to be covered can be done with what can be best described as gold leaf. The sheet stock you work with is so very thin because you need nothing to fill a cut/undercut void as in common inlay work.
Easily hammered out from thicker stock by the worker when and as needed right at the bench.
The effect of the final work is generally to appear as an inlay that is flush with the steel surface. So ultra thin is the key to the gold work and the attaching teeth.
Some work is all done with the small diameter wire. Building a larger area by winding the wire around in the shape desired right on the surface, burnishing in as you go. It's pieces of the wire laying side by side or around like a coiled rope, but done right the joints won't show.
The rough-up is generally done to an entire area with in a border on a piece.
The the gold is laid onto the 'teeth' carefully. It will grab and hold where you place it!, there is little room for 'moving things around' so it's a very precise, tedious work.
Figures and shapes can be oversize and then carefully graver trimmed to final shape once they are on the surface.
The spurs showing outside of a free standing overlay can be planished flat,,gold, steel teeth and all to return the steel to a polish appearance. The spurs showing in the voids in the work or even around the edges can be left there and often are.
They appear very dark, almost black in color even on polished steel because of the total shadow they cast and are used as a background element to the art.
(The same technique is used to shade figures both inlayed and cut.)
The teeth spurs will some times be seen spikeing through the thin gold, especially after the pieces are blued.
The fewer the better as far as quality of the work. You shouldn't have to level the roughened area to remove any overly long barbs before the gold is applied. Doing so will dull the surface and load it up with dirt and grit anyway making the effectivness of the surface to grip the gold much less.
Carefull workmanship is the key.
Heat blue, charcoal blue, ect were common finish techniques.
Details on the gold itself were mostly placed with punches though some very light cuts are possible. More of a burnish cut than a sliceing one. There is little thickness to work with.
Properly done, it's a secure way to attach the overlay metal. If the rough-up isn't done right, it'll start to come apart,,especially after bluing/finishing and some handling.
I've used the same technique for attaching my gold work inlay and overlay work for the past 35+ years.
Before that I was cutting flat stock out to size and inlaying it for figures. Very time consuming and tedious.
It's not rare for engravers to use it in attaching inlays. Some use it as added insurance along with under cuts and dovetails to hold the metal in place,,others use it exclusively. How well the area is prepared makes all the difference in it's effectiveness.
As always there's different tricks and ways to doing this work but that's the basics of it. I've done a little of it (new work) over the years and have restored and repaired more of it, especially on Spanish cartridge firearms.
Some of it was fantastic work,,very highest of quality workmanship. Others, not so good,,and some I've seen was down right crude.
Sorry for the long post...
