Worm Holes

I don't care what Steven Hawking says, worm holes exist and right in my
latest ring.

I think I have learned the hard way what Peter warned me about in private so
I thought it would be useful to share my experience with the beginners that
may be lurking here.

I am making a ring for my wife and after casting, forging to shape, filing
and sanding, I was pretty happy with how it looked except for a very tiny
speck that refused to sand away on the bottom.

So, I made a bezel and soldered it to the ring and this went well and I felt
like I had conquered Everest at least.

After pickling, tumbling and more sanding, the tiny speck turned into a pit
which in a few hours became a hole and another pit right next to it. More
sanding elsewhere and more pits appeared that could not possibly have been
pores opened up by sanding as I was at 400 grit and the ring was pounded to
blazes to forge it to finger size.

So, whence the holes?

I had a bunch of scrap silver from earlier experiments with different
solders, solft, hard and everything in between. I melted this down with
some old sterling sprues to get the weight up to what I needed and poured
away.

The first clue that something was strange was that the top of the buttons
were a dull grey color instead of either dirty copper or silver.

I poured this several times with more and more sterling but always got the
same wierd color but the part finished like silver.

It didn't pour very nicely either but that is another story.

Anyway, I suspect that Peter's warning about getting lead into silver being
a potential disaster, is a warning worth heading. It is also just possible
that I inadvertantly included one of my zinc patterns into the mix. Zinc
being a generic term for my hodge podge of casting metal for patterns.

I made several more ring castings today but started with fresh fine silver.
Hopefully, my wife will still have a ring in the morning... it really is
very pretty if you can ignore the worm holes.

js


--
PHOTO OF THE WEEK: http://schmidling.netfirms.com/pow.htm
Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com

Sounds like porosity.



Your metal melting temps are too high, either casting or soldering, where
ever the holes are. If they are small enough you can burnish them away, or
you can finish your piece with a rough finish, but once porosity, always
porosity. Sometimes you can open the hole with a ball burr and solder over
it, re-finishing to your liking...



Chuck

Gallery Jewelers



"Jack Schmidling" wrote in message
...
I don't care what Steven Hawking says, worm holes exist and right in my
latest ring.

I think I have learned the hard way what Peter warned me about in private
so
I thought it would be useful to share my experience with the beginners
that
may be lurking here.

I am making a ring for my wife and after casting, forging to shape, filing
and sanding, I was pretty happy with how it looked except for a very tiny
speck that refused to sand away on the bottom.

So, I made a bezel and soldered it to the ring and this went well and I
felt
like I had conquered Everest at least.

After pickling, tumbling and more sanding, the tiny speck turned into a
pit
which in a few hours became a hole and another pit right next to it. More
sanding elsewhere and more pits appeared that could not possibly have been
pores opened up by sanding as I was at 400 grit and the ring was pounded
to
blazes to forge it to finger size.

So, whence the holes?

I had a bunch of scrap silver from earlier experiments with different
solders, solft, hard and everything in between. I melted this down with
some old sterling sprues to get the weight up to what I needed and poured
away.

The first clue that something was strange was that the top of the buttons
were a dull grey color instead of either dirty copper or silver.

I poured this several times with more and more sterling but always got the
same wierd color but the part finished like silver.

It didn't pour very nicely either but that is another story.

Anyway, I suspect that Peter's warning about getting lead into silver
being
a potential disaster, is a warning worth heading. It is also just
possible
that I inadvertantly included one of my zinc patterns into the mix. Zinc
being a generic term for my hodge podge of casting metal for patterns.

I made several more ring castings today but started with fresh fine
silver.
Hopefully, my wife will still have a ring in the morning... it really is
very pretty if you can ignore the worm holes.

js


--
PHOTO OF THE WEEK: http://schmidling.netfirms.com/pow.htm
Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com

On Tue, 07 Sep 2004 18:05:37 -0700, in àõ "Gallery"
wrote:

Sounds like porosity.


Of course it's porosity. the question is why there is porosity. Overheating
sterling, on it's own, won't always give you porosity in sand casting (which is
what Jack was doing) if the metal is protected from gas absorption by a flux
covering during melting. Under that condition, one would have to get it very hot
indeed before anything much happened to the melt, since sterling is just silver
and copper, with nothing much else that would burn off or be damaged by higher
temps. It is more likely to do so with lost wax casting due to potential
reactions between the investment (which, being gypsum based, contains sulphur
compounds) and the molten metal which can generate gases in the mold cavity that
lead to porosity. This isn't generally a factor in sand casting. Overheating
also can give porosity when the molten metal dissolves more gas from the flame,
or atmosphere, while molten, which then must come back out of solution when the
metal solidifies. This indeed could be the problem., and is especially common
with fine silver, which is known for it's ability to dissolve prodigous amounts
of oxygen when molten, which spits back out again as the metal solidifies. But
in Jack's case, he mentioned that his metal may well have contained significant
amounts of scrap containing solders, both silver solders and perhaps remants of
soft solders. That would mean the silver had amounts of things like zinc or tin,
or worse, lead, and other low melting metals also alloyed in it. These metals
can volatilize or oxidize when the silver is melted, as the molten sterling can
exceed the boiling points of some of those metals, and the result is very
noticable gas porosity. Other potential causes are uneven pouring trapping air
bubbles, or metal too cool, also trapping pockets of air when the metal fails to
fully fill the cavity before solidifying. Or, a common cause is shrinkage
porosity, when the outer surface of the casting solidifies forming a skin, and
the sprue solidifies enough to stop the availability of additional molten metal,
before the interior of the casting is fully solid. Then that interior section,
as it solidifies, shrinks (as do most metals when the cool), but cannot pull
additional metal from the sprue to make up for the shrinkage, and it literally
pulls itself apart, forming voids and interior tears and gaps. These can
sometimes appear as bubbles as well as very fine pinpoint porosity in a layer
just under what initially appeared to be a good sound casting. And then there's
the whole topic of sprues, both size and placement. More an issue with lost wax
casting, but also with sand casting... Sprues generally need a cross sectional
area equal to or slightly greater than the cross sectional area of the model
where they attach, and should be attached at the heaviest points of the casting.

cheers

Peter