Hi, Mike.
Looks like you have all the correct answers, already.

The rosin core solder is really meant for electrical/electronic
assembly. Electronic components normally are coated with a thin solder
coat during manufacture, so when the user solders, the flux doesn't
have much work to do in cleaning the work.

I think you are wanting to solder brass that does not have a solder
coating. In this case, the flux has a really hard job of cleaning all
the surface of the brass. Oil from your hands, dust in the air, cooking
fumes and who knows what else, have put a very thin layer of
contanimation on your brass. The flux you use will have to dissolve
this contanimation and move it away from the solder, as you apply heat.
Solder will not adhere to the brass where any contanimation is living.

I think you need to find some acid core solder. When this is heated,
the flux decomposes into an acid that eats away the contanimation layer
and lets the solder make contact with the freshly exposed brass
surface. This type of solder used to be available in hardware plumbing
sections. Plumbing now is forced to use lead-free solder, so I don't
know if the flux is still acid or not. The lead-free solder will also
work for your "hard solder" needs.

In all cases, be prepared to wash your project with hot soap and water
and then rinse will. Any acid flux left on the brass will still be
active and will eventually turn the brass to a green color.

Are you using a soldering iron to make the joints for your project? The
hard solder will require a higher temperature than lead/tin solder.
Perhaps 40-50 degrees hotter. Depends on the solder. Your iron may not
be up to the job if it is designed for lead/tin solder.

Good luck on your project. Let us know how it works for you and what
you learn along the way!

Paul in Redmond, OR
mj wrote:
I'm doing some brass model building and the book that I am using as a
guide (by Gerald Wingrove) mentions hard and soft solder. What am I
looking for as far as differences? I suspect the "hard" solder has a
higher melting point (silver solder???) than the soft solder. The stuff
that I got at Radio Shack has this on the label:

Standard Rosin-Core Solder
60/40 (does this mean 60% lead/40% tin?)
.062 dia
8 oz.

I suppose that this is more a "soft" solder. What specs should I look
for in a "hard" solder.

Sorry for all the dumba** questions, but I gotta get this figured out.

Thanks

Mike