Air Bubbles on Gold Sovereigns

[LawrenceChard]

Among of the many interesting features I have seen on gold sovereigns are air bubbles. These undoubtedly exist on other coins, but I can't remember seeing them on other coins, probably because I examine a lot of sovereigns quite closely.

I commented on a recent post that a raised pimple on the obverse of an (1972?) shield sovereign may have been a tiny air bubble.

Here is an example we photographed a few days ago:

Although I see from the filename that it is a half sovereign, not a (full) sovereign. (I did say  I can't remember seeing them on other coins, but I am now worried about my short term memory, and I can't remember having Alzheimer's).

In the main obverse shot, the raised lump is very clear, although it is hard to see on the close up. With any such unusual feature, it is natural to immediately check the other side to see if there is any corresponding feature. In this case, there is not:

This is evidence that the coin was struck with the raised lump, and that it was not caused be any post production damage.

It could have been caused by some indentation on the obverse die, but it does not have the right appearance for that, so the only logical explanation is an air bubble.

Almost all metal casting is prone to porosity caused bu air or gas bubbles in the melt, which remain after solidification. These are likely to be spherical or ovoid at first, but when the cast ingot is subsequently rolled, many times, into a flat sheet or strip, the air bubble get squeezed so they become longer, wider, and flatter. Sometimes the bubble reaches the surface, in which case it is likely to show as a crack or flake in the strip, and subseqently in the blank planchet.

When the planchet is struck to become a coin, the air bubble undergoes further compression and, again, may burst or reach the surface, creating a flake with a sharp, usually ragged edge. If the bubble does not burst, it is likely to form a raised, convex, lump, which consists of a layer of metal overlying the trapped air bubble.

Some may consider this to be a mint error, but I consider it to be an interesting feature, which helps to demonstrate the production process. As coins are mass produced, we should expect the unexpected, and accept that some seemingly random things will happen.

I don't think feartures like this add much value to the coin, nor should they detract from its value. 

I believe most true numismatics should try to have a few coins with unusual features in their collection.

We have photographed quite a number of air bubble and surface flake coins in the past, and I will try to remember to add them to this thread when I re-discover them.

 

Edited April 26, 2022 by LawrenceChard

[dicker]

Many thanks for the photos and the description - very interesting.  

I am guessing that the depression / air bubble would not materially impact the weight of the coin?

Best

Dicker

[LawrenceChard]

1 hour ago, dicker said:

Many thanks for the photos and the description - very interesting.  

I am guessing that the depression / air bubble would not materially impact the weight of the coin?

Best

Dicker

I think that's a good guess, and a good question.

Although we have weighed some of them, I have not noticed any being lightweight, so I suppose I should be more careful to check in future. I doubt that all individual sovereigns get weighed after striking.

It would not bother me to own any lightweight ones, especially if it was because of an interesting feature.

 

[sovereignsteve]

5 minutes ago, LawrenceChard said:

I doubt that all individual sovereigns get weighed after striking.

I thought they certainly used to do so in the days when they were currency. Didn't they have fancy, automatic weighing scales? I believe a great number were rejected and melted down for re-minting.

[LawrenceChard]

5 minutes ago, sovereignsteve said:

I thought they certainly used to do so in the days when they were currency. Didn't they have fancy, automatic weighing scales? I believe a great number were rejected and melted down for re-minting.

Last night I was reading page 19 of The Royal Mint by Ansell, but it's hard going, small print, no chapters, with rather small diagrams, uneven print, etc.

But yes, there was a description of some kind of automated weighing machine.

[LawrenceChard]

Here's another sovereign minting "feature":

The mark shown is a dent, but it is an irregular shape, and importantly, there is no corresponding bulge or damage on the reverse:

I believe this is evidence that some debris, possibly some metal swarf, got onto the obverse die before striking.

 

[paulmerton]

What's equally exciting is that this alludes to the likely existence of air bubbles inside some coins.

Who knew they had some genuine 19th/20th century air in their collections?!

[Pete]

Might find all sorts of stuff in coins from our Royal Mint knowing their QC these days. 😅

[StackemHigh]

20 hours ago, Pete said:

Might find all sorts of stuff in coins from our Royal Mint knowing their QC these days. 😅

Might even find an old pair of speedos from @LawrenceChards last visit to the rm!

[LawrenceChard]

7 minutes ago, StackemHigh said:

Might even find an old pair of speedos from @LawrenceChards last visit to the rm!

My Speedos seem to be famous. Do you think I should put them in a celebrity auction for charity?

[Stuntman]

34 minutes ago, LawrenceChard said:

My Speedos seem to be famous. Do you think I should put them in a celebrity auction for charity?

Why not auction them as a Non Fungible Token instead, so the 'lucky' winner doesn't have to 'enjoy' the Speedos' err... original patina?

[LawrenceChard]

15 minutes ago, Stuntman said:

Why not auction them as a Non Fungible Token instead, so the 'lucky' winner doesn't have to 'enjoy' the Speedos' err... original patina?

I used to think N.F.T. meant No F****ing Trousers. 

This would mean I would have No F****ing Trunks! 

😎

[greendragon]

its the fungible bit that always worried me!

you can have strange experiences with fungi

[LawrenceChard]

19 hours ago, greendragon said:

you can have strange experiences with fungi

That's very similar to one of my old chat up lines "You can have some great experiences with a fungi like me!"

😎

Edited September 26, 2021 by LawrenceChard

[greendragon]

12 hours ago, LawrenceChard said:

That's very similar to one of my old chat up lines "You can have some great experiences with a fungi like me!

😎

followed no doubt by " i grow on you" 

[paulmerton]

2 minutes ago, greendragon said:

followed no doubt by " i grow on you" 

There's not mushroom left in the forum database for all these jokes.

[LawrenceChard]

15 hours ago, LawrenceChard said:

That's very similar to one of my old chat up lines "You can have some great experiences with a fungi like me!"

😎

 

2 hours ago, greendragon said:

followed no doubt by " i grow on you" 

 

2 hours ago, paulmerton said:

There's not mushroom left in the forum database for all these jokes.

To the tune of "Magic Mushrooms" by Perry Como, lyrics and music by Psylo (Si) Binn. 😎

[paulmerton]

On 23/09/2021 at 20:20, LawrenceChard said:

These undoubtedly exist on other coins, but I can't remember seeing them on other coins, probably because I examine a lot of sovereigns quite closely

Here you go then, one from the cheaper end of the spectrum...

Actually, it still has a lot in common with the modern Sovereigns - it's almost the same colour and is worth at least 300x the face value!

[LawrenceChard]

1 hour ago, paulmerton said:

Here you go then, one from the cheaper end of the spectrum...

Actually, it still has a lot in common with the modern Sovereigns - it's almost the same colour and is worth at least 300x the face value!

That is good spotting, pun not intentional, and a good photo. How about showing the obverse, which I would expect to be normal, but it would also show the date.

Stuff like this is interesting!

😎

[paulmerton]

18 minutes ago, LawrenceChard said:

That is good spotting, pun not intentional, and a good photo. How about showing the obverse, which I would expect to be normal, but it would also show the date.

Stuff like this is interesting!

😎

Prepare to be surprised, for the obverse also has an air bubble!

[paulmerton]

I wonder if it's just the plating that has bubbled. Hard to tell.

Incidentally, googling for "air bubbles on pennies" turned up some very unexpected results! 🍆

[LawrenceChard]

30 minutes ago, paulmerton said:

Prepare to be surprised, for the obverse also has an air bubble!

Double bubble!

(Sounds like something from Shakespeare!)

Being 1994. it should also be a copper plated steel one.

As it looks minty, it is possibly from a mint set.

 

[LawrenceChard]

16 minutes ago, paulmerton said:

I wonder if it's just the plating that has bubbled. Hard to tell.

Incidentally, googling for "air bubbles on pennies" turned up some very unexpected results! 🍆

I was going to say that it was more likely to be air bubbles in the ingot casting, getting squeezed in the rolling process, then expanding when stamped in the coining press. 

This is the process which I attribute to air bubbles on gold sovereigns, but your comment about "unexpected results" prompted me to take a look.

It seems like many of them are because people mis-spell pennies as penis, vice versa, or some other combination of spelling errors. Now this thread will almost certainly spin off a tangent!

However, there were also some numismatic search results.

The first https://coins.thefuntimesguide.com/coins-with-bubbles-in-them/, was a slight revelation, because until now, I had not given any thought to air bubble forming between planchet and plating, but it seems like this is quite common.

There are a number of things in the above page which cause me to doubt the expertise or logic of its author, although I believe that much of its content is probably correct.

First, it is strongly US-centric, as though the only coins which exist are American ones. I find this syndrome to be quite common in Americans, and not just related to coins.

He states "Unfortunately, most bubbled coins that are found in pocket change are just exhibiting a form of damage.", and...

...  "The most likely way that a bubble forms on a coin after it’s been struck is through exposure to intense heat.

In fact, virtually all bubbles you see on clad coins simply resulted from heat damage."

While this may be correct, he then goes on to treat his readers as morons:

"Let me repeat that…"

Unless this is intended to demonstrate how clever and superior he is.

Here in the UK, we have never used "clad" coins, which are produced using 3 (usually) sheets of metal laminated together. It is almost certain that the fact they are laminated means it is more likely for air pockets to get trapped between the layers. If the lamination is done after rolling the ingots into sheets, then the air pockets or bubbles were retain their original size and shape until the blanks were struck converting them into coins. At this stage, they could form raised bubbles in a similar manner to solid (monolithic) coins, although because of the difference in processing, I would expect them to be different in some ways.

Joshua, the Coin Editor at TheFunTimesGuide, later explains that most "bubbled" coins are clad onea "almost certainly heat-damaged — exposed to fire, most likely." This may be accurate, but he then captions a poor quality photo "This coin has ripples that were caused by exposure to intense heat:" There is a difference between ripples and bubbles.

He than engages in some more repetition:

"I wanted to emphasize that point — because so many people have shown me photos of their dimes and quarters with bubbles and, with great hope, believe they have a rare or valuable error coin.

Sadly, these coins are almost always caused by the coin being left in a fire, thrown into a fire pit, intentionally singed with a blowtorch, or another similar situation."

Followed by: "Of course, millions of coins are exposed to fire each year, in many cases through accidental purposes. So it’s easy to understand why there are so many coins with raised bumps floating around out there in circulation." 

His use of the word "millions" sounds like exaggeration and inaccuracy. While he may be correct, saying "many", or " a large number"... would be more credible.

A touch more repetition:

"What was that?… You think it’s gas bubbles on your coin?

Perhaps. It’s possible that the bubble on your clad coin was caused by some chemical reaction between clad layers, ..."

And when he ways "but these generally originate back to post-mint heat damage.", it sounds rather like "back to the future".

This: "If your coin was made from a solid alloy, such as a pre-1982 Lincoln cent or Jefferson nickel, then it’s much more likely that the bubbling originates from something in the minting process and is, therefore, a real error coin." makes it sound like he does not know what.

"Then there are the numerous (and I mean numerous!) plating blisters on copper-plated zinc cents made since 1982." This is the first time he has mentioned plating as opposed to cladding. And he really does like repetition.

The UK has made most of its "copper" coins from copper-plated steel since 1992, so we could expect to see similar flaws on these, although zinc may be more susceptible than steel. It does remain likely that any such additional process will make anomalies occur more frequently.

"These plating errors occur when the outer layer of copper fails to properly bond to the coin’s zinc core. Air inside these pockets (or voids) can expand, appearing as bubbles."

He seems to use "layer", "plating", and "cladding", rather interchangeably. "Plating" almost certanily implies electo-plating, and it is difficult to imagine or understand how "the outer layer of copper fails to properly bond to the coin’s zinc core" It is extremely unlikely that plating could or would include an air bubble or void (whatever he means by void). If there was no electrical contact between the substrate and the electrolyte, then the affected area would not become plated.

I will excuse him for calling American cents pennies, as he appears to be American"

"Sometimes, a small amount of gas will occur inside a solid-alloy planchet. When the coin is struck, the incredible heat generated from the striking will cause the gas to explode inside the coin. This will cause a small raised dome on the coin."

I think when he uses the word "incredible", he actually means "large amount of". I believe, in fact know, that the process of striking produces considerable heat, so for me, this is perfectly credible. It is also likely that he is confusing "heat" with "temperature". I am also sure that the gas does not "explode". It may expand or become compressed, but this is not the same as an explosion.

Striking of coins does involve great force and pressure, because of the kinetic energy, some of which gets converted to heat energy, and some of which is transferred to the metal of the planchet causing it to flow into lower pressure areas, such as the incuse parts of the die. Any gas which is pressurised will also tend to flow into lower pressure areas. This flow is likely to continue for a short time after the strking pressure is removed. This is the most likely cause of air bubbles.

 

There was another site / page http://www.michael-coins.co.uk/GBAir Bubble 1p.htm which attempted an explanation:

""Air bubble" in coin

A. Bubbles in a coating applied over a casting are caused by trapped porosity. 

Heat causes air or moisture trapped in porous pockets in the substrate to rupture through the coating as the air escapes. 

Bubbles in coating over a steel part also are most likely caused by trapped air or moisture."

This explanation sounds very confused. The same page also says "A couple of tiny ex-carbon spots on cheek and on bubble". It is unclear what he means by "ex-carbon spots".

 

As your penny appears to be "minty", it is unlikely that the bubbles were caused by any post-production fire or high temperature, otherwise it would bave become discoloured.

 

 

 

 

[paulmerton]

19 minutes ago, LawrenceChard said:

I was going to say that it was more likely to be air bubbles in the ingot casting, getting squeezed in the rolling process, then expanding when stamped in the coining press. 

This is the process which I attribute to air bubbles on gold sovereigns, but your comment about "unexpected results" prompted me to take a look.

It seems like many of them are because people mis-spell pennies as penis, vice versa, or some other combination of spelling errors. Now this thread will almost certainly spin off a tangent!

However, there were also some numismatic search results.

The first https://coins.thefuntimesguide.com/coins-with-bubbles-in-them/, was a slight revelation, because until now, I had not given any thought to air bubble forming between planchet and plating, but it seems like this is quite common.

There are a number of things in the above page which cause me to doubt the expertise or logic of its author, although I believe that much of its content is probably correct.

First, it is strongly US-centric, as though the only coins which exist are American ones. I find this syndrome to be quite common in Americans, and not just related to coins.

He states "Unfortunately, most bubbled coins that are found in pocket change are just exhibiting a form of damage.", and...

...  "The most likely way that a bubble forms on a coin after it’s been struck is through exposure to intense heat.

In fact, virtually all bubbles you see on clad coins simply resulted from heat damage."

While this may be correct, he then goes on to treat his readers as morons:

"Let me repeat that…"

Unless this is intended to demonstrate how clever and superior he is.

Here in the UK, we have never used "clad" coins, which are produced using 3 (usually) sheets of metal laminated together. It is almost certain that the fact they are laminated means it is more likely for air pockets to get trapped between the layers. If the lamination is done after rolling the ingots into sheets, then the air pockets or bubbles were retain their original size and shape until the blanks were struck converting them into coins. At this stage, they could form raised bubbles in a similar manner to solid (monolithic) coins, although because of the difference in processing, I would expect them to be different in some ways.

Joshua, the Coin Editor at TheFunTimesGuide, later explains that most "bubbled" coins are clad onea "almost certainly heat-damaged — exposed to fire, most likely." This may be accurate, but he then captions a poor quality photo "This coin has ripples that were caused by exposure to intense heat:" There is a difference between ripples and bubbles.

He than engages in some more repetition:

"I wanted to emphasize that point — because so many people have shown me photos of their dimes and quarters with bubbles and, with great hope, believe they have a rare or valuable error coin.

Sadly, these coins are almost always caused by the coin being left in a fire, thrown into a fire pit, intentionally singed with a blowtorch, or another similar situation."

Followed by: "Of course, millions of coins are exposed to fire each year, in many cases through accidental purposes. So it’s easy to understand why there are so many coins with raised bumps floating around out there in circulation." 

His use of the word "millions" sounds like exaggeration and inaccuracy. While he may be correct, saying "many", or " a large number"... would be more credible.

A touch more repetition:

"What was that?… You think it’s gas bubbles on your coin?

Perhaps. It’s possible that the bubble on your clad coin was caused by some chemical reaction between clad layers, ..."

And when he ways "but these generally originate back to post-mint heat damage.", it sounds rather like "back to the future".

This: "If your coin was made from a solid alloy, such as a pre-1982 Lincoln cent or Jefferson nickel, then it’s much more likely that the bubbling originates from something in the minting process and is, therefore, a real error coin." makes it sound like he does not know what.

"Then there are the numerous (and I mean numerous!) plating blisters on copper-plated zinc cents made since 1982." This is the first time he has mentioned plating as opposed to cladding. And he really does like repetition.

The UK has made most of its "copper" coins from copper-plated steel since 1992, so we could expect to see similar flaws on these, although zinc may be more susceptible than steel. It does remain likely that any such additional process will make anomalies occur more frequently.

"These plating errors occur when the outer layer of copper fails to properly bond to the coin’s zinc core. Air inside these pockets (or voids) can expand, appearing as bubbles."

He seems to use "layer", "plating", and "cladding", rather interchangeably. "Plating" almost certanily implies electo-plating, and it is difficult to imagine or understand how "the outer layer of copper fails to properly bond to the coin’s zinc core" It is extremely unlikely that plating could or would include an air bubble or void (whatever he means by void). If there was no electrical contact between the substrate and the electrolyte, then the affected area would not become plated.

I will excuse him for calling American cents pennies, as he appears to be American"

"Sometimes, a small amount of gas will occur inside a solid-alloy planchet. When the coin is struck, the incredible heat generated from the striking will cause the gas to explode inside the coin. This will cause a small raised dome on the coin."

I think when he uses the word "incredible", he actually means "large amount of". I believe, in fact know, that the process of striking produces considerable heat, so for me, this is perfectly credible. It is also likely that he is confusing "heat" with "temperature". I am also sure that the gas does not "explode". It may expand or become compressed, but this is not the same as an explosion.

Striking of coins does involve great force and pressure, because of the kinetic energy, some of which gets converted to heat energy, and some of which is transferred to the metal of the planchet causing it to flow into lower pressure areas, such as the incuse parts of the die. Any gas which is pressurised will also tend to flow into lower pressure areas. This flow is likely to continue for a short time after the strking pressure is removed. This is the most likely cause of air bubbles.

 

There was another site / page http://www.michael-coins.co.uk/GBAir Bubble 1p.htm which attempted an explanation:

""Air bubble" in coin

A. Bubbles in a coating applied over a casting are caused by trapped porosity. 

Heat causes air or moisture trapped in porous pockets in the substrate to rupture through the coating as the air escapes. 

Bubbles in coating over a steel part also are most likely caused by trapped air or moisture."

This explanation sounds very confused. The same page also says "A couple of tiny ex-carbon spots on cheek and on bubble". It is unclear what he means by "ex-carbon spots".

 

As your penny appears to be "minty", it is unlikely that the bubbles were caused by any post-production fire or high temperature, otherwise it would bave become discoloured.

 

 

 

 

I'm glad you enjoyed dissecting that page . I had also ended up reading it once I had navigated my way past all the members.

I had always assumed plated and clad were synonymous up until now, so thanks very much for that insight.

So to conclude, you reckon these are legitimate air bubbles inside the steel component? That seems a lot more exciting than a bubble under some cladding. Pressing the big bubble with my thumbnail hasn't caused it to cave in, so that also ties in with the bubble being in the steel, as a layer of electroplated copper must surely be super thin and fragile.

[LawrenceChard]

44 minutes ago, paulmerton said:

I'm glad you enjoyed dissecting that page . I had also ended up reading it once I had navigated my way past all the members.

I had always assumed plated and clad were synonymous up until now, so thanks very much for that insight.

So to conclude, you reckon these are legitimate air bubbles inside the steel component? That seems a lot more exciting than a bubble under some cladding. Pressing the big bubble with my thumbnail hasn't caused it to cave in, so that also ties in with the bubble being in the steel, as a layer of electroplated copper must surely be super thin and fragile.

Enjoyed? Yes, I suppose I did.

I estimate there were between 3 million and 7 million pages involving primary male sexual organs in combination with air or bubbles, so either you're a fast reader, or this has been a long-standing investigation. 😎

A few other words get used incorrectly meaning plating, such as layered, or coated.

There is also "gold-filled" which sounds llike something filled with gold, but means the opposite, usually rolled gold, where the gold is "filled" with base metal.

The thumbnail or press test you tried is a good one in my opinion, and I agree, a bubble under a very thin plating would probably burst or distort much more easily.

It might be worth asking the Royal Mint, via its "chat" feature, if they can provide an opinion.