A bit rough but someone has loved it!

[mas4t0]

3 hours ago, vajo said:

Mark aqua regia changes only the state of matter. You can turn gold from tetrachlorgold back to gold. You can not destroy gold and silver. 

 

 

Aqua Regia does not only change the state of matter, the Gold is oxidised and has undergone a chemical reaction. The Gold can easily be reduced to return to pure Gold, but this is more than a change of state. A state change refers classically to solid, liquid, gas, and plasma. This is not a state change (i.e. melting the Gold to turn solid Gold into a liquid), but is a chemical reaction involving Oxidation of Gold; just as rust is formed through the Oxidation of Iron.

 

In a chemical reaction none of the matter is used up (that would be a nuclear reaction). If we consider complete combustion of Methane:

• Methane + Oxygen → Carbon Dioxide + Water

But this does not tell the whole story and could give rise to misunderstandings regarding conservation of mass (i.e. an assumption that mass is not conserved when in fact it is). The Stoichiometric equation which is properly balanced accounts for conservation of mass by including the ratios of the respective reactants and products:

• CH4 + 2O2 → CO2 + 2H2O

Since:

• 1 mole methane = 12 +4 =16g
• 2 mole oxygen = 2×32 = 64g
• 1 mole CO2 = 12 + 32 =44 g
• 2 mole water=2 × 18 =36g

From the balanced reaction:

• 1 mole(or 1 molecule or 16 g) of CH4  reacts with
• 2 moles (or 2 molecules or 64 g) of oxygen to give
• 1 mole (or 1 molecule or 44 g) of CO2 and
• 2 moles (or 2 molecules or 36 g) of water.

For the gaseous system at STP (Standard temperature and pressure):

• 22.4l methane reacts with
• 44.8l of oxygen to give
• 22.4l of CO2  and
• 44.8l of water.

 

No mass is gained or lost. No nucleus can be "destroyed" other than by radioactive decay, fission, fusion or potentially annihilation; this is true of every element and is in no way specific to Gold and Silver.

 

Conservation of mass is a fundamental premise of all Chemistry and is in no way unique to Gold and Silver; I don't understand where this misconception is coming from.

[mas4t0]

6 hours ago, vajo said:

 

For silver, when you have 1oz of silver and it gets patinated what is the weight of that 1oz silver? When you remove the patination what is the weight of that 1oz silver now?

 

 

Your scales would not be accurate and precise enough to measure the loss of mass, but if you remove the patina you have removed material and as such the mass would now likely be in the range of 0.99999999999999999999 oz as opposed to the original 1 oz. Prior to removal of the patina (assuming you have exactly 1 oz of Silver), the total mass may be in the region is 1.0000000000001 oz on account of the extra Sulphur you've you've collected on the surface.

 

Silver has an atomic mass of 107.8682 u.

Avogadro's Constant tells us that there are 6.02214076 × 10^23 atoms per mole.

 

1 oz is ~28g.

1 mole of Silver would weigh ~108g

 

1 oz of Silver is ~0.26 moles (28g/108g)

So your 1oz of Silver contains ~1.56 x 10^23 atoms (0.26 * 6.02214076 × 10^23).

Thats: ~156000000000000000000000 atoms.

 

I'd guess that after removing the patina, you might be down to 155999999999999999999000 atoms.

 

That would be a loss of 1000 atoms. You'd never pick it up on a scale, and the atoms would still exist (you wouldn't have annihilated them), but you would have forever removed them from the object you'd removed the patina from.

 

I don't know what's contentious here. This is elementary Physics and Chemistry which have been very well understood for a long time.

 

If you want a practical example of this, consider Silver plating:

• The plating is typically 10 to 25 microns thick.
• The lattice constant of Silver is 0.409 nm (think of this as the length of one side of the cube occupied by a single atom of Silver).
• So a 10 micron plating of Silver would be ~24,500 atoms thick (10e3 / 0.409) and a 25 micron plating would be ~60,000 (25e3 / 0.409) atoms thick.

 

These platings wear through quite readily and there's tens of thousands of atoms. The mass of the object would change but the losses would be so slight that you wouldn't detect them with a scale; you would however see the loss of material as the copper beneath was exposed. I've never taken a piece of silver plated material, left it to patinate, removed the patina and then repeated the process until the plating is gone, but I assure you that the plating would be lost this way over a long enough span of time.

[vajo]

Mark you can remove the patina bringing the electrons back into the silver.

Salt warm water and aluminiumfoil. 

The patina is not the silver. Its like dirt on a window.

[mas4t0]

1 hour ago, vajo said:

Mark you can remove the patina bringing the electrons back into the silver.

Salt warm water and aluminiumfoil. 

The patina is not the silver. Its like dirt on a window.

 

The tarnish is Silver Sulphide (Ag2S), it is reacted Silver on the surface and not a layer of dirt.

 

I presume the reaction you're describing is:

3 Ag2S + 2 Al → 6 Ag + Al2S3

 

It's an electrochemical reaction, making use of Aluminium's greater affinity for Sulphur than Silver's. By "bringing the electrons back into the silver" you are reducing the Ag2S to Ag.

 

Although the ion exchange would presumably be taking place at the surface of both metals, Silver Sulphate is very slightly soluble in aqueous solution (i.e. where water is the solvent) so there would be some losses into the solution. The solubility is listed as 6.21e−15 g/L (25 °C), so the losses would be extremely small, but they would not be zero.

[ROKUJURO]

Chris,

 

as far as I know, an element gains weight when it reacts with another one. Iron with a given net weight will be a bit heavier when rust forms on the surface. Removing the rust (and I don't mean with an angle grinder!) will reduce the basic weight of the iron.

 

I would be very surprised to learn that silver reacts differently.

[Rivkin]

5 hours ago, mas4t0 said:

The atomic nucleus of a stable element will not (ever) decay. Gold and Silver are no different from any other stable element in this regard.

Additionally, Gold can be Oxidised and fully dissolved in Aqua Regia; Gold can be Oxidised.

Oxidation is, technically speaking, loss of electrons. An atom (or atom group) loses electrons when it is oxidised - conversely, an atom or atom group that gains such electrons is reduced.

Gold “does not oxidise” according to our experience because it ranks very high in the so-called electrochemical series (Standard electrode potential), a list of how easy it is to oxidise chemical species.

As Gold is above oxygen (the commonest oxidiser), no oxidation occurs to it.

However, the reaction with Aqua Regia does involve Oxidation of Gold to form Chloroauric acid (HAuCl₄) in solution via the following reaction:

 

....

Probably said by a chemist. 

Stable nuclei can and do decay. The difference is that after a typical "decay" what remains will have higher energy compared to the original; unstable elements have lower energy after the decay. So compared to a collection of particles a stable element is a global equilibrium, unstable is local. In both cases there is an energy barrier that prevents the decay, but in the stable case the mechanisms for overcoming this barrier must involve absorbtion of energy... which with a negligibly small probability can occur even in the "ordinary" life.

 

Oxidation is technically loss of electrons if the bond is ionic. The gold oxides one has to practically worry about however are covalent (shared electrons). Actual shakudo will include a healthy portion of covalent AuO, its violent oxidation method creating nanoparticles small enough to exhibit such combinations.

However if gold is not powdered into nanoparticles, you don't have to think hard about the oxidation since most "conventional" oxides are either metastable or are stable in a very limited window of parameters. They can form, but operational conditions of a typical electronic component are sufficient for them to quickly dissolve back into gold, which will "stick" back to gold's surface. Compared to gold's plasticity this is a second order contributor to "why gold's surface always changes". Because its a second order and leaves no permanent change, its typically not widely discussed.

[mas4t0]

2 hours ago, Rivkin said:

....

Probably said by a chemist. 

Stable element can and do decay. The difference is that after a typical "decay" what remains will have higher energy compared to the original; unstable elements have lower energy after the decay. So compared to a collection of particles a stable element is a global equilibrium, unstable is local. In both cases there is an energy barrier that prevents the decay, but in the stable case the mechanisms for overcoming this barrier must involve absorbtion of energy... which with a negligibly small probability can occur even in the "ordinary" life.

 

Oxidation is technically loss of electrons if the bond is ionic. The gold oxides one has to practically worry about however are covalent (shared electrons). Actual shakudo will include a healthy portion of covalent AuO, its violent oxidation method creating nanoparticles small enough to exhibit such combinations.

However if gold is not powdered into nanoparticles, you don't have to think hard about the oxidation since most "conventional" oxides are either metastable or are stable in a very limited window of parameters. They can form, but operational conditions of a typical electronic component are sufficient for them to quickly dissolve back into gold, which will "stick" back to gold's surface. Compared to gold's plasticity this is a second order contributor to "why gold's surface always changes". Because its a second order and leaves no permanent change, its typically not widely discussed.

 

My mistake; what I meant to say is:

 

"The atomic nucleus of a stable isotope will not (ever) decay spontaneously."

 

This is by definition.

 

Some "stable" isotopes (i.e. no radioactivity has been observed for them) are predicted to have extremely long half-lives; over 1 quintillion (1,000,000,000,000,000,000) years. However, if any radioactivity is observed (i.e. if it can be detected experimentally at any point) those isotopes will be re-classified as radioactive.

 

I think you're describing Cosmic Ray Spallation, but (on earth) it only occurs in the uppermost few meters of earth's atmosphere.

 

Cosmic rays cause spallation when a ray particle (e.g. a proton) impacts with matter, including other cosmic rays. The result of the collision is the expulsion of particles (protons, neutrons, and alpha particles) from the object hit.

 

Quote

 

Neutrons in the atmosphere result from cosmic-ray spallation interactions with nitrogen and oxygen nuclei. A typical reaction is a 1 GeV proton fragmenting a nitrogen necleus into lighter charged particles and simultaneoously emitting a couple of neutrons.

 

 

These neutrons can then interact with other nuclei, as in the formation of (radioactive) Carbon-14 which is continually formed by the interaction of neutrons with (stable) Nitrogen-14. Note though that the radioactivity comes about from the transformation of the stable nuclide to a radioactive nuclide, which will then decay in accordance with its half-life.

 

The strong force binds the nucleus together, while the weak force is responsible for radioactive decay and an important participant in nuclear fission and fusion.

 

Regarding covalent Vs ionic bonding...

 

If the compound were truly covalent (with identical electronegativities) all the oxidation states would be zero, as in the case of diamond where the bonding is between only carbon atoms.

 

By convention all shared electrons are assigned to the more electronegative nuclei (for the sake of oxidation state), but this is clearly not the case in practice (especially where the electronegativity is very similar).

[vajo]

Ok guys. After 2 Beer, 2 Ouzo and one Prosseco reading your scientific explanation i hope that I'm right that silver patina did not reduce the amount of Ag by giving up electrons?

 

 

[ROKUJURO]

Chris,

perhaps try with more Ouzo?

[vajo]

4 minutes ago, ROKUJURO said:

Chris,

perhaps try with more Ouzo?

Done!  Now teach me to dance!

Dance? Come on boy..

Alexis Sorbas. 

[cdrcm12]

All,

 

Thanks for all the comments and discussion added to this thread, I didn't expect to gain so much information on metallurgy or chemistry but that's the benefits of having experts on the Board.

 

I've added some further shots showing what could be gaps (layering) within the nakago, consistent on both sides in the same area exposed by fitting adjustments?

 

The pictures also show that the corrosion (sorry I'm using this term) within the sukashi elements looks to be the same as on the surface. I do believe this is now due to rusting over time but still can't quite explain the seppa dai unless the seppa have been very tight against each side of the tsuba from the tsuka/habaki, giving some form of protection?

 

 

 

[Spartancrest]

Colin, not directed at you.  

I just got my Doctorate in Metallurgy from this thread - I should have stayed "lost in space"  [and my head still hurts]

[roger dundas]

I thought the safest place for me Dale over the past 48 or so hours was in bed, under the blankets  away from all of the knowledge flying about. Brain seizure material for my poor old mind.

Roger 2

[Shugyosha]

All I got was:

 

[ROKUJURO]

In fact, this is all very basic chemistry and not rocket science. No one needs to learn it by heart right now to be able to enjoy Japanese art, but it helps immensely to explain the processes of what we see and feel as corrosion - or rust, if we talk about iron.

[roger dundas]

There was just so much information Jean and where I am in life I have to be fed just a teaspoonful at a time or my brain overheats and I choke.

Not really, I am just being ridiculous but there was a lot going on and most of you will add some of it to your existing knowledge and mix it in. I am finding harder to do of late

Roger 2.

[Ford Hallam]

Colin,

 

those latest images are really far more revealing. I can see what you mean with respect to there perhaps being some indication of structure in the iron. If you'd like to send it to me, I'm in Dartmouth, I'll remove all of the rust/corrosion product safely, photograph at high magnification and resolution the resulting surface and then re-apply a suitable patina. I'll do this for free and post the images here so we can all see and learn more, and you'll get a much better tsuba back to boot. If you'd like to take up my offer message me for my studio address etc.

 

And having read with interest the superbly detailed chemical and metallurgical discussions this thread has engendered I must add one last bit of info myself.

 

As I think we've now established, and contrary to Bavarian school of metallurgy dogma , silver does indeed covert to a corrosion product, namely silver sulphide.

What I'd like to add is some real world experience that is directly relevant to tosogu and may be of interest to fellow students of the art.

 

As a restorer I must have worked on at least a couple of dozen of bronze vases that featured fine silver wire inlay. Typically the wire was around 0.5 mm in diameter and once inlaid it had been polished flat. These were mostly Meiji period pieces so around the time I worked on them perhaps 90 to 100 years old at most. Without exception the silver wire was black, unless someone had previously buggered around with them in which case the bronze patina was knackered too. Sometimes the black 'scale' (silver sulphide) had grown so thick that it'd started to flake off. This flaking happens because the silver sulphide is very brittle compared to the underlying silver. Changes in temperature and the resulting differing degrees of expansion and contraction of the silver and sulphide layer causes a break where they interface. The newly revealed fresh silver appears a dull white at this point and is quite rough in appearance, almost stony. It's quite a fiddly and time consuming process to restore a degree of polish to this corroded silver.

 

With the silver sulphide removed what was once a smoothly polished surface now has a very clear groove in it that you can actually catch your finger nail in. Consider that the wire was 0.5 to begin with ( an average based on those pieces I've restored and had to re-inlay) , some thickness is lost in the inlay and polishing process so we can estimate perhaps a depth of around 0.35 remaining. this is in fact what I've measured myself when dealing with tiny fragments that have fallen out. What is remarkable is that the action of the hydrogen sulphide in the air in converting the pure silver (it's almost always fine/pure silver in Japanese inlay work) into silver sulphide has easily consumed half or more of the original silver in 100 years. Sometimes actually all of it.

 

This is also why we find that gold nunome-zogan tends to survive more frequently than silver numome-zogan. Even on the same piece of work the silver will inevitably be more fugitive compared to the gold. This is a very real problem I've had to deal with countless times. Higo tsuba collectors will know this well too I suspect, tea inspired wabi-sabi aside those Jingo tsuba rarely have much silver left. Some applies to Hizen and Jakushi works.

 

For reference the foil used in this type of Edo period nunome-zogan is generally around 0.02mm thick, that's about as thick as a sheet of standard 100 gsm printer paper or 20 microns thick.

In the Jewellery industry the accepted standards for gold plating is 0.5 microns  (or more)  for standard plating and 2.5 microns for heavy (sometimes termed Vermeil, from the French term for mercury gilded bronze) plating.  And 20 microns of fine/pure silver (jun gin) sometimes doesn't last 100 years on a tsuba whereas gold that thin can survive in wet acidic soil for thousands of years virtually untouched. Well, the gold survives, naturally, but any additional copper or silver in the alloy is inevitably attacked and is lost to the gold artefact. This leaching out of the non-gold elements is what causes that characteristic frosted rich fine gold appearance of ancient archeological gold. 

 

 

[b.hennick]

Thanks, Ford! I have been enjoying this thread. I appreciate what got have added to it. Mark you brought me back to the old days when I  had to teach chemistry rather than my usual biology. If I was still teaching, I would certainly share your posts with my class. Well done gentlemen!👍👍

[cdrcm12]

Hi Ford,

That's a very generous offer and I can't refuse, PM sent.

 

It will be of real interest to the NMB members to see the transformation.

 

 

 

[GRC]

like Barry, I'm also a science teacher (although not retired yet).

I just wanted to comment on a few little statements to maybe help a bit, and avoid having some members (without science backgrounds) build up some accidental misconceptions   

 

Ford just corrected this one, perhaps inadvertently. silver sufide vs silver sulphate:

The black silver "tarnish" that you see building up on old silver is Ag2S, is called silver sulfide, not "silver sulfate" Ag2(SO4) (silver sulphate for the UK spellers out their). These are two different substances with different physical and chemical properties. For example: silver sulfide is black, whereas silver sulfate is white.

23 hours ago, mas4t0 said:

Silver Sulphate is very slightly soluble in aqueous solution (i.e. where water is the solvent) so there would be some losses into the solution.

 

Silver sulfide forms a covalently bonded "network solid" with only slight ionic properties, and is considered to be insoluble in most solvents, including water. (https://en.wikipedia.org/wiki/Silver_sulfide) 

ie. It doesn't dissolve much at all, in just about any type of substance that would dissolve other things, so the loss in water would be pretty much imperceptible.

 

Just some semantic wording on this one, but I believe the ideas are fundamentally sound when taken together as a whole:

21 hours ago, ROKUJURO said:

an element gains weight when it reacts with another one. Iron with a given net weight will be a bit heavier when rust forms on the surface. Removing the rust (and I don't mean with an angle grinder!) will reduce the basic weight of the iron.

The main thing to clarify is the use of the word "element".

The word "element" gets muddied by the fact that it can be used to refer to a single atom (like 1 atom of silver) or a grouping of atoms of 1 type (like a block of 100% pure silver).

 

It might be more clear to rewrite it like this (although much wordier... so it's always a pain in the butt to explain science clearly in a chat or forum-post format):

 

A metal object will gain weight when the surface atoms react with other elements/compounds in such a way to produce some type of "corrosion product", but only if that "corrosion product" stays on the surface of the metal object.

The reason for this weight gain is that atoms from an external source in the environment are reacting with the surface atoms of the metal object in such a way as to combine with them to form "compounds". ie New atoms are being added to the metal object, therefore the object will gain the additional weight of the new atoms. That's the whole "conservation of mass" concept that was stated earlier by Mark H.

 

Now on to the use of "element" in the context of weight changes:

A block of "elemental" pure silver, will gain mass when it tarnishes, because sulfur atoms are being added to its surface as the black tarnish forms.

 

But, technically an "element" as a "single atom" doesn't necessarily gain weight in a reaction...

If an element ("single atom") does change weight in a chemical reaction, the atom itself will have only gained, lost or shared electrons, which are so small in size and mass that they are not measurable on a practical level.

 

In the case of silver tarnish, a single atom of silver will be constantly gaining and losing the two electrons that are now being shared in the covalent bond between it and an the adjacent sulfur atom in the silver sulfide network. One silver and one sulfur are now sharing one electron each with each other, and these two electrons will be travelling (teleporting) back and forth between the adjacent silver and sulfur atoms. And again, this gain and loss of electrons would be imperceptible on any practical level of measurement.

 

Now back to Colin's tsuba and iron corrosion products:

In some cases the corrosion products (like the iron oxides in Colin's tsuba) have different physical properties that the original metal object, making them structurally more brittle, which can allow them to "break away" from the metal object over time. In the case of Colin's tsuba, the pitting we see is caused by the loss of this more flaky, brittle, iron oxide material ("rust").

So this tsuba has definitely lost some weight that could easily be measured (if we had the original mass).

 

But if there is simply some reddish dusting on the surface of a steel tsuba, and none of it has flaked off yet, then the steel tsuba will have also gained weight, similar to the way the silver tarnish added weight to a block of silver. However, In this case, oxygen atoms will have been added to its surface as it "rusted" to form the iron oxides. 

 

Tying the idea of change in properties back to silver tarnish:

The fact silver sulfide that it forms a "network solid" helps explain Ford's observations that it can actually flake off in chunks on really old silver.

I've never seen that, but unlike Ford, I've never had a piece of silver that was so old that it had built up enough of this solid silver sulfide. 

Cool "fun facts" for the classroom, thanks Ford. 

 

Effects of rust or tarnish removal on weight:

So given all of the above information, any time you polish away the rust from steel or tarnish from silver, you will be physically removing some of the original iron or silver atoms that had been incorporated into the rust or tarnish that you are removing.

 

Ok i'm done now... sorry for being so long winded 

I hope it helps.

[GRC]

2 hours ago, Ford Hallam said:

This is also why we find that gold nunome-zogan tends to survive more frequently than silver numome-zogan. Even on the same piece of work the silver will inevitably be more fugitive compared to the gold.

Just to give a visual to go along with the "fugitive" nature of silver vs gold nunome, the silver does have a tendency to "travel out" from where it started on the tsuba (not my tsuba btw):

 

[Ford Hallam]

Hi Glen

 

I can't claim any credit for correcting the Silver sulphate typo, I didn't see it at all I was only focussed on the black stuff 

 

Your explanation that silver sulphide forms a "network solid' is actually further helpful in going someway to explaining how this conversion actually migrates away from the source silver as on the tsuba you show. I wonder if this is a sort of flowing structure? It does actually come away from the iron ground very easily so It doesn't seem to be significantly bonded at that point of contact. The silver sulphide on the actual silver, on the other hand, is quite strongly bonded. I tend not to use any sort of abrasive methods it removing it, because of the delicacy of the work mostly, so I use a chemical solution to break down the sulphide that is very gentle in its action. I won't mention what it is for fear of unleashing DIY restoration armageddon.

[GRC]

That's an interesting difference to point out Ford...

 

The formation of a network would definitely "rearrange and reorganize" the existing silver atoms into this new network with the sulfur.

So why does it stick better to silver than to iron? 

 

Here's my hypothesis:

 

I could see the silver nunome sliding around more on an iron surface because it was merely "applied" to the iron surface to begin with, so it was never really "integrated" into the iron in any atomic sense. The atoms in the steel below would all be "metallically bonded" to each other so it might be harder for a newly forming network of silver sulfide to "push" its way down into the steel, so it would preferentially "skate" over surface as it grows.

Take the "path of least resistance" so to speak.

 

Conversely, the tarnish buildup on a chunk of silver would actually be "pulling" silver atoms that were actually "metallically bonded" with (and among) the other silver atoms of the block, so maybe the network forms in such a way that it is more "integrated" and woven into the silver block itself. Maybe even forming "peaks" and "troughs" going in and out of the silver block, kind of "locking it in" to a certain degree, rather than the "loose sheet" that seems to form on iron.

 

This is just some deductive reasoning on my part... so I'm not sure if these statements are actually true      

But, it could help explain why the tarnished silver nunome on iron comes off so easily, but the silver tarnish is harder to remove from a silver base.

[ChrisW]

You're a real treasure Ford! For us uninitiated, we're fortunate to learn from you and those with knowledge in this field.

[roger dundas]

Those last half a dozen posts were excellent for me, forever the 'layman'.

Just as a matter of interest, would an application of Renaissance wax have any benefit as to reducing further silver oxidation or is it's use here something not quite kosher ?

 

Ford as you say Chris But Glen too has been forwarding many great observations. Then there is Dale way up there also and Jean (Rokujuro) even with his troubles still posting. Mark too with his technical observations.

And Rivkin whose observations and judgements are looked forward to.

Just brilliant information.

Roger j

[Rivkin]

13 hours ago, GRC said:

Here's my hypothesis:

 

I could see the silver nunome sliding around more on an iron surface because it was merely "applied" to the iron surface to begin with, so it was never really "integrated" into the iron in any atomic sense. The atoms in the steel below would all be "metallically bonded" to each other so it might be harder for a newly forming network of silver sulfide to "push" its way down into the steel, so it would preferentially "skate" over surface as it grows.

Take the "path of least resistance" so to speak.

 

Conversely, the tarnish buildup on a chunk of silver would actually be "pulling" silver atoms that were actually "metallically bonded" with (and among) the other silver atoms of the block, so maybe the network forms in such a way that it is more "integrated" and woven into the silver block itself. Maybe even forming "peaks" and "troughs" going in and out of the silver block, kind of "locking it in" to a certain degree, rather than the "loose sheet" that seems to form on iron.

 

This is just some deductive reasoning on my part... so I'm not sure if these statements are actually true      

But, it could help explain why the tarnished silver nunome on iron comes off so easily, but the silver tarnish is harder to remove from a silver base.

 

Personally I would not take an observation "silver spreads more than gold" in koftgari as absolute.

For some traditional makers Gold has a bad reputation for squishing if its hammered just a bit too aggressively, compared to brass with which one has much better control and sharper image. I would not bet against brass being the actual material in cases when something really stays in place and is sharp. Gold does tend to have more rounded boundaries but obviously more "goldy" look.

Gold on the other hand does not bond well by itself to iron surface - it falls off rather than travels.

At the same time I've seen lower grade silver in particular often "traveling" a lot over the surface and being more uniformly "muted" in color due to oxidation.

Gold is more sensitive to mechanical wear, silver is more sensitive to oxidation and copper content. For some, brass in good hands is a very good material.

[mas4t0]

Thank you Glen for catching that typo, I apologise if I caused anyone any confusion. I'll stick with chemical formula from now on!

 

Regarding solubility of Ag2S, I was answering (what I understood as) a very specific question: whether silver would be lost from a mass of silver if an electrolysis reaction were used to reduce Ag2S to Ag in the absence of any mechanical separation.

 

This reaction is often claimed to not lose any silver in the process; I disagree. The core of my argument was that if nothing else, some infinitesimally small amount would be dissolved into the solution.

 

Do you disagree with this?

 

I realise the solubility is very, very low. At 6.21e−15 g/l you'd get around 1 metric ton of Ag2S dissolved in the Atlantic Ocean. I maybe wasn't clear, I simply meant to state that it's not entirely insoluble.

 

My guess in the above posts was ~1000 atoms in 1 litre of water.

 

The mass of Ag2S which would dissolve in 1 litre of water = 6.21e−15g

The molar mass of Ag2S = ~248g

The number of moles of Ag2S which would dissolve in 1 litre of water is:

6.21e−15g/ 248g = 2.5e-17

 

2.5e-17 * 6.02e23 = 15,050,000 molecules of Ag2S dissolved in 1 litre of water, which means (unless I've made an error) 30,100,000 atoms of silver in that 1 litre.

 

Meaning my guess before could be as much as 30,000x too low.

 

While the solubility is low enough to classify Ag2S as insoluble, it is not truly 100% insoluble (in the binary sense). This is also of course assuming pure water.

 

On 7/16/2022 at 4:49 PM, GRC said:

A metal object will gain weight when the surface atoms react with other elements/compounds in such a way to produce some type of "corrosion product", but only if that "corrosion product" stays on the surface of the metal object.

 

The reason for this weight gain is that atoms from an external source in the environment are reacting with the surface atoms of the metal object in such a way as to combine with them to form "compounds". ie New atoms are being added to the metal object, therefore the object will gain the additional weight of the new atoms.

 

It would probably be more clear to write this in terms of Mass (the quantity of matter in a physical body) rather than Weight (the force acting on the object due to gravity).

 

Conceptually, "mass" (measured in kilograms) refers to an intrinsic property of an object, whereas "weight" (measured in newtons) measures an object's resistance to deviating from its current course of free fall, which can be influenced by the nearby gravitational field.

 

I would say something like:

 

"The mass (i.e. the quantity of matter) of a physical body (i.e. a collection of matter within a defined contiguous boundary in three-dimensional space) will increase if additional matter is bound to it and decrease if matter is removed from it."

 

Or maybe even more simply:

 

"If a physical body has a net gain of matter, the mass (i.e. the quantity of matter) will increase and vice versa."

 

The key concepts are matter and mass and from there, there's not really much more you say; the above is like saying, "If I get more stuff, I'll have more stuff."

 

It doesn't seem worthwhile to say because the definitions themselves are doing the heavy lifting, but that's all we're really saying in the general sense and it works for all scales from the very small (e.g. sub-atomic particles) to the very large (e.g. galaxies).

 

On a macro scale, if you amputate and eat a chicken's leg (bones and all), you will have gained mass and the chicken will have lost an equal amount of mass. If the chicken eats your leg, you will have lost mass and the chicken will have gained an equal amount of mass. This is of course all zero sum overall.

[mas4t0]

The spreading of Ag2S is clearly due to the lower density.

 

The density of Ag2S is 7.23 g/cm³

The density of Silver is 10.49 g/cm³

 

So Ag2S will occupy ~50% more volume (per gram) than the unreacted Silver (and as discussed ad nauseam, there's more mass in the reacted Ag2S on account of the added Sulphur).

 

Presumably the expansion would occur evenly in all (unobstructed) directions, similar to thermal expansion.

 

I can't really envisage it spreading sideways without an accompanying growth in height, as it's not a fluid (which would tend to flow and be "flattened" under its own weight due to gravity). I'd expect more of a "mushrooming". 🍄

 

Is there something else going on here that I'm missing?

 

Has anyone seen this in practice; does the Ag2S grow vertically (i.e. at a normal to the surface) in addition to spreading sideways (i.e parallel to the surface)?

[DirkO]

I'll offer up this extreme close-up of inlay that has travelled and expanded a bit. It has been reworked to clearly show the silver expansion. Also I don't know where I read it, but this bleeding of silver is supposedly actually a desired feature amongst collectors.

 

[mas4t0]

9 minutes ago, DirkO said:

I'll offer up this extreme close-up of inlay that has travelled and expanded a bit. It has been reworked to clearly show the silver expansion.

 

 

Thank you Dirk.