You need old engineers. Moden engineers avoid the stuff.
Depends on your "lead". It's a metal that's more commonly encountered
as alloys than as pure. Even slight impurity levels make a big
difference to its properties, particularly melting point and hardness.
The melting point of pure lead is about 325°, but common lead alloys
may drop as low as 180°C. Lead is also soft, but a few percent of
anything can make it 4 times as hard (Brinell numbers)
There's also the issue of "eutectic" behaviour. Lead alloys don't
simply melt at one temperature - they have a "pasty" range where a
solid and melt with different compositions can co-exist. At one
composition (63/37 Sn/Pb) this range is zero and the alloy melts
cleanly at single temperature (the lowest melting point for this alloy
system). Outside this temperature, the "pasty" range can be as much
as 100°C - essential for some soldering techniques, such as "wiped"
joints. For lead alloys, the lower limit of this range stays at a
fairly constant temperature and the upper limit increases to the
values for the pure metals.
Roofing lead is handled as thin sheet, so needs to be ductile. It's
one of the few grades that's reasonably pure, but even this will have
0.3% antimony in it..
Linotype metal (old newspaper type) had 12% antimony and 4% tin in it,
to make it particularly hard and also to control shrinkage on cooling,
so that it could be moulded to shape easily.
Solder is effectively free of antimony (it's bad news in solders) but
contains lots of tin. Famously this depends on purpose, from 20% tin
for plumber's lead-working solders through to 50% tin for
coppersmithing, 60% tin in electrical solders and modern lead-free
solders that are practically all tin.
"Scrap lead" generally resembles wheel weights and other rubbish.
It'll have about 3% antimony and a couple of percent of almost
anything else; arsenic, bismuth, copper, tin. Scrap lead from
batteries can have all sorts of rubbish in it (calcium, antimon,
arsenic, selenium), some of which is most unpleasant (I'm told
submarine batteries really shouldn't be handled hot except by the
Yes, but there aren't that many of them. It's worse if you _over_
heat it. Generally the dross on the top is the stuff to watch out for
- dust from lead oxide, even when cold, is more of a hazard than metal
By far, the best thing is the electrically-heated bottom-pour pot used
for bullet casting. This lets you draw clean melt off the bottom, away
from the dross on top.
If you're top pouring, then almost any steel or iron vessel will work.
Chinese supermarkets sell big ladles that work well (even for bronze).
As a kid I used to re-cast my scrap lead in a ladle meld of steel
scaff pipe stick-welded to a flat plate. You'll be wanting some
tallow or rosin as a flux and a hardwood stick to scrape the dross
clean away before pouring. Tallow is still available from electrical
suppliers, but it's sold as a threading lubricant for conduit, not as
a soldering flux.
Gosh Andy, I wish I'd said that ;o))
All I can add is the obvious - to do it out of doors or at the very least to
avoid inhaling the vapour that will inevitably rise from the pot.
Oh, and I learned at the weekend that "old" lead (dunno how old, but
probably pre war) is more ductile because it still has a trace of titanium
and zinc which made all the difference, apparently. These days, the titanium
is removed to make the oxides for white paint.
The usual impurities missing from "old" lead (pre-1943) are the nuclear
isotopes. If you're making a lead castle as a screen for a counting
chamber, then re-melting old lead is much better than freshly-smelted
lead as it has a lower background count.
This is the same effect that led to the German fleet in Scapa Flow
being "quarried" for their steel armour plate. It's WW1 steel, so it's
radiologically clean, and because they were scuttled in shallow water
they're relatively easy to access and aren't war graves.
I'm puzzled by Ti and Zn impurities making it ductile. I'd strongly
expect _any_ impurity to make it less ductile (as a general principle
for all alloys). Loss of ductility doesn't come about by mixing in a
metal "that's brittle", it's because it's a mixture rather than a pure
metal and that will always play havoc with tidy crystal lattices.
Ti is a fairly common impurity in metals, as it's a very common
element. For pigment use though, it's the Ti oxide that's used. This is
quite easily mined in the oxide form and there's no shortage of it. The
high cost of Ti has always been due to the cost of smelting it -
difficult and expensive, using the Kroll process. If there was any way
to extract Ti from lead as a metal, then this would surely go as the
valuable metallic Ti, not for conversion to the oxide pigment.
Zn is also a funny thing to find as an impurity. As anyone brazing or
pickling brass can tell you, Zn boils (or usually sublimes) so readily
that it's easily removed from an alloy just by heating it. Now this
would be a little hot for mere lead, but even so Zn tends to disappear
from where you want it, more readily than it shows up where you don't.
Lead sourcing has certainly changed from 100 years ago. Back then it
was mined as primary lead, these days it's significantly supplied by
recycling. I wouldn't be at all surprised that old lead is ductile, but
I'd guess at that being because all modern lead is now likely to
contain appreciable antimony from recycled hard lead, rather than a
shortage of Ti or Zn.