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Fluxes for silver

Would you use two different fluxes for fine silver versus sterling

I’ve been using “Gesswein Hard Soldering Flux” on fine silver, but
haven’t had a lot of luck. Sometimes the solder flows perfectly.
Twice the solder has stayed solid, just getting reddish-brown with
heating, sticking to the silver but not melting. Sometimes the flux
forms a white, crystalling coating on the silver.

I’ve just E-mailed Gesswein asking what is in this flux. It’s a
yellow liquid, if that tells you anything.


Gesswein just called to say that their yellow "Hard Soldering Flux"
has borax, ammonia phosphate, boric acid, and yellow dye. They also
suggested using one of their “preflux” products in conjunction with
the yellow flux, to extend the range working temperatures.