keep solder from spreading

What's a good way to keep solder from flowing or wetting copper or brass parts being soldered- sort of like an anti-flux. I recall seeing something posted here about it, but can't locate it.

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http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=3866785&k=solder%20mask
or, you can use ordinary paper masking tape, but you'll have to clean off the burnt mess afterwards.

Cydrome Leader wrote in rec.crafts.metalworking on Sun, 13 Mar 2011 21:48:15 +0000 (UTC):
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It's called solder mask. You can get it in tape form from granger.

Cydrome Leader wrote:
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I haven't tried this yet, but I hear tell that after cleaning the heck out of pipe and fitting, one fluxes both and assembles them, just like always.
Here's the kicker. *With a pure acetylene flame* you coat the exterior of the joint with carbon black, turn the oxygen back on and heat as per usual.
Apply solder to the seam and the carbon black will prevent wetting to undesirable areas.
Clean up and the joint will have that pro look.
--Winston

I've heard of "White Out" correction fluid being used for that. Haven't tried it though.
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Charles Lessig wrote:
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Hmmm, I dunno about that.
"Titanium dioxide dust, when inhaled, has recently been classified by the International Agency for Research on Cancer (IARC) as an IARC Group 2B carcinogen possibly carcinogenic to humans."
http://en.wikipedia.org/wiki/Titanium_dioxide
--Winston

wrote:
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ALL DUST, organic and inorganic, is deadly to human lung tissue. But we knew that. What's the beef? Is some gov't agency trying to prove itself useful, current, and viable? Again?
-- You create your opportunities by asking for them. -- Patty Hansen

Larry Jaques wrote:
(...)
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Perhaps 'deadly' is too strong a word? I've cleaned up some *extremely* dusty places without protection and suffered coughing, wheezing and other entertaining sound effects and I'm still kicking.
If I had it to do over, I would have donned a respirator but I'm older and more cowardly now.
Lesson learned. Catastrophe luckily avoided.
--Winston

But one will slowly have trouble with breathing.
COPD as they say - and black lung on non-smokers.
Furnace and foundry work is harsh. Mowing and breathing in sand dust. Living in some areas of the world and breathing the air with blowing dust / sand...
Martin
On 3/13/2011 8:44 PM, Winston wrote:
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wrote:
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No, it kills tissue every time, though it may not kill you. It also irritates the lungs enough to screw up your immune responses and can result in cancer. Mother Nature sez "Thou shalt not inhale particulates, dumbass."
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Ditto here, even when I mow my lawn, spray, or blow. I survived brake dust as a mechanic in me yout.
-- You create your opportunities by asking for them. -- Patty Hansen

Right - if you can't absorb and melt it away it is bad.
Currently a turkey is trying to ban LED lighting because he believes there is arsenic in the LED.
Millions of times as much in a peach pit. But never mind a non-thinker on a mission to screw up the US.
Martin
On 3/13/2011 7:54 PM, Larry Jaques wrote:
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Cydrome Leader wrote:
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I heard that scribbling a lot of soft graphite pencil on the surface works. I tried it once, and it did appear to have that effect, but I haven't tried it extensively.
Chris

For many years men dressed solder irons and once true, use the rubber on their shoe (inside of the heal) to coat all the tip except the wetting location.
I've also used rubber erasers that I heat up with a heat gun and then wipe over areas.
Modern workers don't need to worry - the joint is small. But they make resists that you can paint on. Just like solder resist used on printed circuit boards.
I'd think on some items it might be best to use High temperature (glass) tape. Woven glass. or Fiber glass with glue on the back.
I think you can buy resist at local Radio Shack stores.
Martin
On 3/13/2011 4:48 PM, Cydrome Leader wrote:
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I'll try this graphite trick. I should have been more clear that the soldering here is basically small pipe-like components, being done with a mapp torch and acid flux, not a soldering iron.

Google "braze stop off". "Stop off" is the key term. We used to mix up several kinds for vacuum brazing applications. basically a paste made from stuff like aluminum oxide dust and a vehicle, sometimes alcohol. Could be water, I suppose.
Pete Stanaitis -----------------
Cydrome Leader wrote:
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IIRC yellow ochre is the default. Of course, just being filthy works, too; but most people find that out when they fail to clean and solder won't go where they want it to, rather than through intentional exploitation of filth.

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Its knowledge, and craft. The knowledge bit is is straightforward
prepare the area to be soldered only flux it up use a HOT iron. No pissy electronics ones - at least 100watts, with a big tip, conical shaped. get in and out fast. Dont try to tart it up, you will stuff it.
The Craft is:- Have a practice run first, unless your an idiot. , you will be OK. No debate, no issues, no preffered brands, its not rocket science, just an old craft skill.
Andrew VK3BFA.

On 3/13/2011 5:48 PM, Cydrome Leader wrote:
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I have used regular "white out" correction fluid for this lots of times. works great. The water based stuff is makes less obnoxious fumes but seems to be hard to find in the store sometimes. The solvent based stuff works just as well, but I use with good ventilation so I don't inhale the fumes when I heat it.

Al wrote:
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Try "white out for copies," maybe? I'd have thought Vaseline, but depending on your heat source, that might make nasty fumes.
Or, just don't slop molten solder all over everything. ;-)
Cheers! Rich

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There is such a thing as "anti-flux", you can search on it. However, when I silver braze, I use an old dodge I read about, which is to use a soapstone(talc) marker and rub around the work area with it. It works. Probably anything that spoils the clean metal surface and resists the action of the flux would work. Talc quailfies since it's resistant to heat and doesn't react with much of anything.
Stan