In article , Cydrome Leader
wrote:

I botched up the edge of a stainless steel darkroom sink with a saw.
Whoops. The cut into the edge is cosmetic, but really really ugly. I
called the manufacturer of the sink to see how to best patch the cut which
is a tad over 1/6" wide and about 5/8" long. It passes though a folded
edge of what seems to be 3 layers of 24 guage stainless. I belive it's 304
but am not 100% sure, and forgot to ask.

I was told, yes it can be soldered and to use 50/50 lead/tin solder, any
really active fluxes for stainless and do not use a torch as it will
oxidize the metal.

Harris makes a liquid flux that seems to be fine for stainless. The issue
is it seems people really like silver solder for stainless. Even the old
timer at the local welding store seemed baffled by using 50/50 on
stainless.

Obviously both can and do work. Any ideas on why one might use a silver
solder vs the 50/50 stuff? Harris makes something called Stay-Brite solder
which appears to be something close to or the same as silver solder or
potable water stuff. Is it the same, or can plain lead free plumbing
solder be used on stainless?

There are special fluxes for soft-soldering stainless steel. These
fluxes contain phosphoric acid.

There are also a number of standard soft solder (meaning it melts below
800 F) varieties for work on stainless steel.

Plumbing supply houses usually carry these fluxes and solders.

Do not try to hard-solder stainless steel sinks unless they are made of
a low-carbon stainless steel alloy that will not be ruined if heated to
a red heat.

The term "silver solder" is ambiguous. There are silver-bearing hard
and soft solders. The key is the temperature needed to solder.

Joe Gwinn