Since no one else has jumped in yet, I will offer what I know.
There are two (at least) major problems here.
If you overheat gold filled, the gold will melt/diffuse/alloy (not
sure technically which) into the brass and then you have just
It you solder brass (with or without gold) to silver, especially
assuming it is single-clad gold filled, it is very easy to overheat
that combo. As I understand it, brass=copper+zinc. Silver
solder=silver+copper+zinc. So it is very easy to turn your
sterling+brass into a puddle of solder. I’m here to say, I’ve done it
on a number of occasions, because I don’t generally use brass so I
tend to forget. The brass will “collapse” into this puddle, usually
tipping rakishly in the process.
So, can it be done? yes. Are you likely to screw it up until you
figure it out? I’d say so.
I’ve been much happier using gold/silver bimetal to applique
lower-cost gold onto pieces. Lower-cost than solid sheet, that is. I
get 22 karat/sterling bimetal from Reactive Metals, though I believe
Hauser & Miller also has it. It costs a good deal more than sterling,
but you are soldering sterling to sterling; there is no issue with
hallmarking, as your piece is all gold and silver; and the 22k
contrasts beautifully with sterling, whereas 14k is pale and
anemic-looking. It hardly shows up at all. And it is harder to screw
up 22k than 14k because it has a much higher melting point.