They are soldered and, probably, laser welded together.
Five bands are prepared, the four top ones and the thin underlying
band. They are then assembled. The diamonds may be set either before
or after assembly.
The band of what looks like calibre cut stones, which they call
"Clou de Paris" (Parisian nail), is actually a band of gold surfaced
by physical vapor deposition (PVD). This is the most technically
difficult part of the process as it requires specialized industrial
If the deposition material is sufficiently stable under the heat of
soldering then that band could be coated before assembly. If the PVD
coating would be compromised by the heat of soldering then it may be
possible to assemble first and then mask the rest of the ring during
coating, similar to masking off part of a piece while
My suspicion is that both soldering and laser welding are used
during assembly to keep the heat away from the PVD surface.
Because of the PVD coating, the ring’s construction is highly
technical but not really mysterious.
Those look like one side is cast with a more elaborate pattern and
part of it is a sleeve that passes under the others, then the other
side is slipped over the sleeve and soldered or welded on. That gives
it that smooth inside look.
a few years ago i worked for a manufacturers and when we made a
similar style of sleeve ring. we used a tungsten/diamond lathe to cut
away the metal for the coloured bands, leaving the gold band as part
of the sleeve. slip the coloured bands onto the sleeve and use a kick
through (heavy machinery for flat band rings although i don’t know
its real name), to stretch thering to size and hold the coloured
bands firmly in place. we would then turn the ring on a wooden chuck
and burnish from the inside with a tungsten or polished stone
burnisher to bring a little lip up against the coloured bands to make
sure they couldn’t escape - no soldering was required. For us the
stone setting and finishing of the bands was done prior to