Whizzing

"Nick Knight" wrote in message
...

I'm wondering if it might be like butter. You know, if you have a stick,
or
tub of margerine in the fridge and pull it out, it's rock-hard. Let it
warm
up, even a little, and it gets softer. There's a point where it's not
melted, but it's pretty moldable. Of course, it's easy to melt, but it
needn't be liquid to spread it over a piece of bread.

Turning the top layer of the silver to true liquid would be pretty
destructive. Getting it plyable, I would think, would be the goal. I
don't
know at what temperature that would occur.

Nick

Here is where imperfect analogies can easily mislead. The comparison
appears, on the surface, to be an attractive one, but Sterling freezes at
about 750C. Your butter analogy presupposes temperatures above freezing,
yes?

Sterling may be annealed, by heating to around 550-600C and soaking at that
temperature. ("Soaking" is a misleading term - it means keeping it at that
elevated temperature for a while - until all transformations are complete.
Nothing to do with water.)

Any softening of silver would therefore require heating to this temp - and
this would only *reduce* its hardness, not actually convert it to a
"mouldable" state. Its still relatively hard in the annealed state - at
least according to our human senses.

Between about 750C-950C Sterling is in a "mushy" state - a solution of alpha
(a Cu-Ag solution) plus liquid silver. Around 950C the remaining alpha
dissolves in the silver and the whole lot melts. In this so-called "mushy"
stage, it could be argued that the metal is "mouldable", except that the
introduction of any foreign object (forming tool - wire brush - whatever)
would immediately freeze out more alpha - and all bets are off.

Of course, the above paragraph presupposes that there is a source of heat
sufficiently intense to raise the silver that much in temperature. A wire
brush certainly cannot do that. In no way, shape or form.

Silver cannot be made pliable in the way you suggest. Heating to just under
750C would allow something somewhat analogous to forging, but the silver
would still be solid - not pliable or mushy. You can't just "push it
around". Also, you would be perilously close to melting portions of it at
that temp. Silversmiths don't do it that way. Its too "iffy". I've never
tried forging (hammering very hot metal - not "counterfeiting"!) silver (why
would I?) but I've tried some alloys of bronze and brass and they have split
and "crushed" (splintered) rather than neatly compressing. I suspect silver
responds similarly. One thing is for sure. It *doesn't* respond like
butter.

--
Jeff R.
(of course, Nick won't see this - but who cares?)

"Anka" wrote in message
ups.com...

Yes, I'm agreeing with Jeff. Experto credo.

~Anka


Thanks Ank, but no. Definitely not an expert.

Substitute the word "metallurgy" for "biology" in the following:
http://www.mendosus.com/whizzing/prof-steve-jones.mp3
and you start to get an idea of my conception of my "expertise" (if I may be
so immodest as to make comparisons with the brilliant Steve Jones).

Its a 139kb, 35 second clip.

--
Jeff R.

On Oct 2, 1:59 am, "Jeff R." wrote:
"Nick Knight" wrote in message

...



I'm wondering if it might be like butter. You know, if you have a stick,
or
tub of margerine in the fridge and pull it out, it's rock-hard. Let it
warm
up, even a little, and it gets softer. There's a point where it's not
melted, but it's pretty moldable. Of course, it's easy to melt, but it
needn't be liquid to spread it over a piece of bread.

Turning the top layer of the silver to true liquid would be pretty
destructive. Getting it plyable, I would think, would be the goal. I
don't
know at what temperature that would occur.

Nick

Here is where imperfect analogies can easily mislead. The comparison
appears, on the surface, to be an attractive one, but Sterling freezes at
about 750C. Your butter analogy presupposes temperatures above freezing,
yes?

Sterling may be annealed, by heating to around 550-600C and soaking at that
temperature. ("Soaking" is a misleading term - it means keeping it at that
elevated temperature for a while - until all transformations are complete.
Nothing to do with water.)

Any softening of silver would therefore require heating to this temp - and
this would only *reduce* its hardness, not actually convert it to a
"mouldable" state. Its still relatively hard in the annealed state - at
least according to our human senses.

Between about 750C-950C Sterling is in a "mushy" state - a solution of alpha
(a Cu-Ag solution) plus liquid silver. Around 950C the remaining alpha
dissolves in the silver and the whole lot melts. In this so-called "mushy"
stage, it could be argued that the metal is "mouldable", except that the
introduction of any foreign object (forming tool - wire brush - whatever)
would immediately freeze out more alpha - and all bets are off.

Of course, the above paragraph presupposes that there is a source of heat
sufficiently intense to raise the silver that much in temperature. A wire
brush certainly cannot do that. In no way, shape or form.

Silver cannot be made pliable in the way you suggest. Heating to just under
750C would allow something somewhat analogous to forging, but the silver
would still be solid - not pliable or mushy. You can't just "push it
around". Also, you would be perilously close to melting portions of it at
that temp. Silversmiths don't do it that way. Its too "iffy". I've never
tried forging (hammering very hot metal - not "counterfeiting"!) silver (why
would I?) but I've tried some alloys of bronze and brass and they have split
and "crushed" (splintered) rather than neatly compressing. I suspect silver
responds similarly. One thing is for sure. It *doesn't* respond like
butter.

--
Jeff R.
(of course, Nick won't see this - but who cares?)

So does the following excerpt about a match being used to melt
hairlines have any chance of being correct

"In yet another form of surface alteration, the surfaces of Proof
coins are heated to actually melt the hairlines or other defects. This
method may involve anything from a match held under the surface for a
few seconds to a high temperature torch selectively applied to a
specific area. Coins altered in this manner sometimes have a wavy look
or different "depth" to the mirrored surface. These clues are
especially noticeable on Proof gold coins, since the surfaces are so
delicate. Also, many Proof gold coins have "orange-peel" surfaces that
are flattened by this method. If the mirrored fields vary across the
surface of a coin, heat treatment of the fields is often the cause"

http://www.pcgs.com/articles/article...d=313&type= 1

"Jorg Lueke" wrote in message
ps.com...

So does the following excerpt about a match being used to melt
hairlines have any chance of being correct

"In yet another form of surface alteration, the surfaces of Proof
coins are heated to actually melt the hairlines or other defects. This
method may involve anything from a match held under the surface for a
few seconds to a high temperature torch selectively applied to a
specific area. Coins altered in this manner sometimes have a wavy look
or different "depth" to the mirrored surface. These clues are
especially noticeable on Proof gold coins, since the surfaces are so
delicate. Also, many Proof gold coins have "orange-peel" surfaces that
are flattened by this method. If the mirrored fields vary across the
surface of a coin, heat treatment of the fields is often the cause"

http://www.pcgs.com/articles/article...d=313&type= 1


18K gold melts at around 1050C.
The hottest part of a match flame is around 800C. (More typically 700C)

Such things would be possible with a pipette-style blowtorch, using Oxy/Acet
or Oxy/Propane, but, by golly, you'd need a steady hand.

All a match could do is fill the hairline with soot.

For silver? Similar story (melts around 950C), but *theoretically* a very
thin ridge surrounding a hairline *could* be elevated in temp to a stage
where a small % of the metal would be molten (*not* all of it), but I
somehow doubt it, considering the duration of a match flame and the
heatsinking ability of the coin.

OK. With a candle?
Unlikely again, due to heatsinking and buildup of soot.

A hairline is a scratch - a depression in the surface. It may or may not
have an associated (tiny - microscopic) ridge built up on either side. It
is fanciful in the extreme to expect that a match would (could) be
sufficiently selective to melt these ridges sufficiently to allow them to
flow back into the scratch.

If this is a representative example of the expertise of PCGS, then I think
we all gave Alan Hagar and Accugrade an unfair time, some years ago.

Fanciful and "simple" explanations for these phenomena are very alluring and
seductive, but they don't stand up to any sort of critical analysis.

I'd go for the pipette. They can direct intense heat to a tiny area.

--
Jeff R.

On Oct 2, 2:39 am, "Jeff R." wrote:
"Jorg Lueke" wrote in message

ps.com...





So does the following excerpt about a match being used to melt
hairlines have any chance of being correct

"In yet another form of surface alteration, the surfaces of Proof
coins are heated to actually melt the hairlines or other defects. This
method may involve anything from a match held under the surface for a
few seconds to a high temperature torch selectively applied to a
specific area. Coins altered in this manner sometimes have a wavy look
or different "depth" to the mirrored surface. These clues are
especially noticeable on Proof gold coins, since the surfaces are so
delicate. Also, many Proof gold coins have "orange-peel" surfaces that
are flattened by this method. If the mirrored fields vary across the
surface of a coin, heat treatment of the fields is often the cause"

http://www.pcgs.com/articles/article...341&universeid...

18K gold melts at around 1050C.
The hottest part of a match flame is around 800C. (More typically 700C)

Such things would be possible with a pipette-style blowtorch, using Oxy/Acet
or Oxy/Propane, but, by golly, you'd need a steady hand.

All a match could do is fill the hairline with soot.

For silver? Similar story (melts around 950C), but *theoretically* a very
thin ridge surrounding a hairline *could* be elevated in temp to a stage
where a small % of the metal would be molten (*not* all of it), but I
somehow doubt it, considering the duration of a match flame and the
heatsinking ability of the coin.

OK. With a candle?
Unlikely again, due to heatsinking and buildup of soot.

A hairline is a scratch - a depression in the surface. It may or may not
have an associated (tiny - microscopic) ridge built up on either side. It
is fanciful in the extreme to expect that a match would (could) be
sufficiently selective to melt these ridges sufficiently to allow them to
flow back into the scratch.

If this is a representative example of the expertise of PCGS, then I think
we all gave Alan Hagar and Accugrade an unfair time, some years ago.

Fanciful and "simple" explanations for these phenomena are very alluring and
seductive, but they don't stand up to any sort of critical analysis.

I'd go for the pipette. They can direct intense heat to a tiny area.

--
Jeff R.

Thanks Jeff. Numismatics like most areas is filled with half right
explanations. Sometimes you can even go back a century or so and
trace a "fact" back to it's erroneous source. I'm sure much of the
information replicated almost verbatim about whizzing comes from a few
if not one original source. I did see an interesting quote about
silver metling due to whizzing, allegedly from the ANA grading guide,
though I haven't found it, I look forward to the citation. It might
be fun to trace such a "fact" back to its source. Unless, of course,
the citation was faulty.

"Jorg Lueke" wrote in message
ups.com...

Thanks Jeff. Numismatics like most areas is filled with half right
explanations. Sometimes you can even go back a century or so and
trace a "fact" back to it's erroneous source. I'm sure much of the
information replicated almost verbatim about whizzing comes from a few
if not one original source. I did see an interesting quote about
silver metling due to whizzing, allegedly from the ANA grading guide,
though I haven't found it, I look forward to the citation. It might
be fun to trace such a "fact" back to its source. Unless, of course,
the citation was faulty.


I'll say.
Take as (another) example the "glass is a supercooled liquid which continues
to flow all its life - hence the cathedral windows which are thicker at the
bottom than at the top" furphy. I bet there's lots of folk who still
believe that urban legend.

Hey!
I wonder if Snopes.com would be interested in whizzing legends?
Somehow, I doubt it. :-(

--
Jeff R.

On Tue, 2 Oct 2007 11:39:45 +1000, "Jeff R."
wrote:

If this is a representative example of the expertise of PCGS, then I think
we all gave Alan Hagar and Accugrade an unfair time, some years ago.

The principal text writer of the articles being discussed is John
Dannreuther. Dannreuther is the founder of PCGS, and a graduate of
the University of Mississippi with a degree in chemistry. His bio
says that he went into the coin business after graduation, so there's
no indication that he actually worked as a chemist.


--


Tony Cooper
Orlando, FL

On Oct 1, 8:09?pm, Jorg Lueke wrote:

So does the following excerpt about a match being used to melt
hairlines have any chance of being correct

"In yet another form of surface alteration, the surfaces of Proof
coins are heated to actually melt the hairlines or other defects. This
method may involve anything from a match held under the surface for a
few seconds to a high temperature torch selectively applied to a
specific area. Coins altered in this manner sometimes have a wavy look
or different "depth" to the mirrored surface. These clues are
especially noticeable on Proof gold coins, since the surfaces are so
delicate. Also, many Proof gold coins have "orange-peel" surfaces that
are flattened by this method. If the mirrored fields vary across the
surface of a coin, heat treatment of the fields is often the cause"

http://www.pcgs.com/articles/article...341&universeid

I spent quite a bit of time Googling to find the flame temperature of
a match without much success. I did find one source that claimed 2000
degrees C which would certainly exceed the melting point of coin
silver. Jeff mentions a much lower temperature...significantly below
it's melting point.

However, regardless of the flame temperature the surface of the coin
would have to be raised to it's melting point. I have extreme doubts
that this would be possible in the "few seconds" claimed in the text
you quoted from PCGS (or even before the match burned out).

Sterling silver anneals at a temperature much lower than it's melting
point and will glow red when it's heated to this temperature.. Do you
think a match could even cause a coin to reach this lower temperature
resulting in the coin glowing red after a few seconds?

Of course, as Jeff mentioned, with a match there would also be soot
deposited on a coin. I imagine the removal of this soot from a proof
coin might be almost as big a problem as the initial scratch.

I learned a few years ago after reading NGC's page on PVC not to rely
on grading services for accurate scientific information.

On Mon, 1 Oct 2007 21:06:36 +1000, "Jeff R." wrote:

Jeff...thanks for filling in the blanks for James. This was my mental vision as
to what was happening but couldn't come up with a way to express it at a late
night hour for me.
Sintering...interesting. Back in the '70s I used sintered stainless steel in
various porosities to introduce a highly volatile gas into a high pressure
polymerization media. The purpose was to disperse the gas in very fine bubbles,
thus increasing its surface area.

Don


"Mr. Jaggers" lugburzman[at]yahoo[dot]com wrote in message
...

Whether metal is moved or removed seems to be the kernel of this entire
discussion. With less than 100% certainty I would say that scratching the
surface of a coin with a pen knife would be akin to making a furrow in
dirt. There would be a ridge on either side of the scratch where the metal
formerly in the scratch would be deposited, and perhaps a few particles of
metal actually detached from the body of the coin and clinging to the tool
or falling to the floor.

I go along with this, James (as demonstrated by my sketch
http://www.mendosus.com/whizzing/gif/ridges-1.gif
but I wouldn't discount too much the amount removed.

... Indeed, one can often see this in a glass. But then if somebody held
a rotating wire brush against a coin, and material were actually being
Removed, I would expect a cloud of metal dust to be constantly in view and,
this procedure being pursued for a long enough time, ultimately the entire
mass of the coin would be converted to this dust, or whatever one cared to
call it.

It's a lot more subtle than that. After I had been whizzing the '43 florin
of my tests for a while, I noticed a silvery sheen on my thumb. I then saw
specks of silvery dust on my workmat.
http://www.mendosus.com/whizzing/jpg/filings.jpg
There was no cloud of metal dust, nor any pile of filings on the floor.


...I don't know if that would be the same as holding a coin against a
rotating grinder wheel, in which case the body of the coin would actually
be much more rapidly converted to tiny particles that would accumulate on
the floor in the vicinity of the grinder.

Dear god, no. No comparison. The grinding wheel is unyielding and solid.
The wire brush is flexible and yields to pressure.

.... With the same less than 100% certainty, I might suggest that the
rotating brush spends very carefully choreographed, but very minimal, time
in contact with the coin surface during whizzing, and that more metal is
moved around than is actually removed.

Can't agree with that. The wire brush has no simple mechanism where it can
"move" metal except for abrasion.

(I was going to save this next bit until someone-or-other had yielded, but
heck...)

One possible (*and* feasible) explanation for the build-up of metal could be
the sintering process. This is, in effect, the shaping of powdered metal
which is heated and compressed to form a new shape. This process is
well-documented. (Bloody brilliant, too!)

In the case of whizzing-induced-sintering I suggest that fine metal
particles are abraded off the surface of the coin, then flung tangentially
at high speed across the surface of the coin, until they strike the edge of
a device (or are flung off onto the workbench). This may well be a trip of
only a mm or two. They are very briefly hot enough to agglomerate in a
rapidly-growing "ridge" of metal powder.

Note: The temperature would nowhere near approach the melting point of
silver. Maybe a couple of hundred degrees C, probably less, but way under
the solidus.

This effect is well-known to metal machinists, who see such agglomerations
build up on (actually, adjacent to) the cutting edge of a high-speed-steel
cutting tool. For us, its a nuisance which must be removed before it
actually impinges on the workpiece and ruins the cut finish. The lumps are
surprising hard and tough, considering that they are built up of fine
powdered metal filings, flung together at high speed. I usually grind (or
oilstone) [is that a verb?] them off, 'cause they're too hard to pick off
with a scriber. Mind you, I'm talking stainless steel here, not Sterling
silver.

The agglomerations of powdered silver dust tend to stick together simply
because they *are* so small and because they are flung with so much energy.
Electrostatics are almost certainly involved, too, but I am not sufficiently
well versed in that to argue that aspect.

The whizzer would then apply a final polish (much more gentle), the effect
of which would be to further compact and consolidate the "sintered" build-up
(*and* shine it up).

When a sintered item is manufactured, the powdered metal is compressed into
a very accurate die (or "mould", if you like) and is then surprisingly hard
on its own - just through the process of compression. Granted, binders
(finer particles) and fluxes (to minimise oxidation during firing) would be
added when this process is done deliberately and commercially. The unfired
sintered piece *is* brittle but remarkably tough considering its structure.
The piece I have seen being sintered (a gear from an automatic transmission)
took a lot of effort to snap in two. It most certainly did not just snap or
crumble. It was surprisingly strong. When fired in the kiln it was, as
expected, almost as strong as solid metal. (Yet porous enough to be soaked
in oil to produce self-lubricating characteristics. How cool is that?)

My hypothetical sintered ridge on a coin device would certainly be brittle
and would never gain the benefit of firing (or would it...?). Nevertheless,
its subsequent polishing would assist its strength, and it would be
supported underneath and on its side, thus providing no easy access for
testing its brittleness. It would not have to be particularly strong to
withstand the rigours of handling a valuable coin should suffer.

Anyways, in a nutshell that's one theory of ridge build-up through whizzing.
No melting, no liquefaction, no softening, no solvents - just abrasion and
agglomeration.

Brickbats, anyone?


... Which, then, occurs more rapidly, the moving of metal, or the removing
of metal? What's the scoop on all this? This geezer would like to know.

Answered? Moving by removing and replacing.
This geezer is comfortable with the mechanics of that theory.

James

"Don Boudreau" wrote in message
...
On Mon, 1 Oct 2007 21:06:36 +1000, "Jeff R." wrote:

Jeff...thanks for filling in the blanks for James. This was my mental
vision as
to what was happening but couldn't come up with a way to express it at a
late
night hour for me.
Sintering...interesting. Back in the '70s I used sintered stainless steel
in
various porosities to introduce a highly volatile gas into a high pressure
polymerization media. The purpose was to disperse the gas in very fine
bubbles,
thus increasing its surface area.

Don


Its a magnificent technology, isn't it!

An apparently solid metal screen, sintered so as to regulate the pore size,
being used for microscopic high pressure filtering...

Heck.

....and I just *love* the way that slugs of alloying metal can be just placed
on top of the item before firing, regulating the actual final alloy of the
part *and* controlling porosity.

The brilliance of the engineers and scientists who invent these techniques
never fails to amaze me. (Not to forget water-jet cutting, laser cutting,
almost *anything* with CNC in its name...)

--
Jeff R.