Corrosion vs. Porosity

[LINCOLNMAN]

As I move into colonials I encounter many details NG copper coins, due to corrosion. However, I see a number of coins with straight grades with seller descriptions that include "minor porosity" or "patches of porosity". Further, I see a number of early coppers that are straight graded that look no better (based on photos) than some of the details coins.

Is this one of those nebulous areas of "market acceptability"? Or, is there an objective test? Or, is it the case that in some instances it appears that the porous surfaces may have been there when struck, owing to an inferior planchet, and the coin is given the benefit of the doubt, being an early copper? 

Lastly, do the EAC folks see things differently corrosion-wise than the TPGs?

[Conder101]

When it comes to the later date coppers (roughly post 1832) and they talk about porosity I would agree that we at EAC are trying to soft pedal corrosion.  For colonials and pre-1796 cents the copper came from any scrap that was available and you could have planchets that were poor quality to begin with.  For those struck between 1796 and 1832 most of the planchets came from England in the bilges of the ship and made the long voyage often submerged in salt water for months, so the surface could be somewhat corroded and porous when the coins were struck.  I will agree though on lower grade coins often times people will try to pass off post mint corrosion as "porosity".

[WoodenJefferson]

Good question, can you tell the difference from say a dug coin that is porous and one struck on a porous plan?

[numisport]

Some modern coppers show porosity in strike weakness and is notable on a few 1950 proof Lincolns where you could find this on Lincoln's shoulder. Most proofs are fully struck but mine was a cameo and an early strike. None the less it was obvious porosity and not planchet marks or corrosion that didn't strike out.

[BillJones]

I usually view "porosity" what's left after the corrosion was gone. As for the "porous" vs. "porous planchet" argument, I think that the "porous planchet" argument is the excuse to push off a porous coin as a "no problem" coin more often than not. I believe that you have to have a fairly high grade coin (at least EF-45 or AU-50 or better) to make the "porous planchet" argument credible. If the coin was struck on a porous planchet the dies would have smoothed out some the porosity when the coin the struck. The porous part should look like it's part the design. To have that you need to have quite a bit of the original mint surface remaining.  I know that's a very subtle distinction, but if you have graded coins for a long time it's possible to make it.

Another aspect of this is die rust. You need to be able tell the difference between a marks made by a rusty die and post mint damage. Once more a high grade coin is necessary to make that distinction.

Here are a couple of examples.

Here is a Mint State Fugio Cent. I am quite sure than any of the roughness you see on this piece, especially on the reverse was on the planchet when the coin was struck.

Sorry, I can't get the picture function to work to do the second coin.

[Insider]

Corrosion is a bad word.  So is buffing (AKA "cleaned").  TPGS's tend to downplay both on the label.  Each happens in degrees.  Sticking with corrosion, it can be active or "set" called "patina."  Corrosion eats into the surface.  When it is removed, the coin is porous.  Nice even porosity is often over-looked.  Uneven deep, scattered, unattractive holes are not.  

[kidrootbeer]

Here's a Great One:

Found a 1797 C-1 1/2C overseas, a gorgeous Brown Fine double struck on a TAL, with TAL edge lettering on the Half Cent edge. Got all that? Sold it to a customer who insisted on having it PCGSed. Long story short, twice it was rejected as "Environmental Damage" even though it was as glossy and brown as a piece of caramel candy.  I called them up, asked them if they knew what the hell they were looking at, and their response to me as that no matter how nice and glossy and brown it looked, the undertype coin was porous so that's that, and it could/would never be graded Problem-Free

[LINCOLNMAN]

On 6/27/2017 at 6:28 PM, allmine said:

1797 C-1 1/2C overseas, a gorgeous Brown Fine double struck on a TAL,

QDB cites two of these in his Colonial book, did you keep it?

[kidrootbeer]

No, I had a customer who became increasingly unhappy that it couldn't be straight-grade holdered. I had it on eBay; so if it's in his book that's where he got the pic from?

[Insider]

On ‎6‎/‎24‎/‎2017 at 5:08 PM, numisport said:

Some modern coppers show porosity in strike weakness and is notable on a few 1950 proof Lincolns where you could find this on Lincoln's shoulder. Most proofs are fully struck but mine was a cameo and an early strike. None the less it was obvious porosity and not planchet marks or corrosion that didn't strike out.

This is not porosity.  The "dings" you are describing that are found on many coins are original planchet surface imperfections.  One numismatist named them "OPSI" marks in the 1970's.  Take a look at any planchet.  These marks are sometimes visible on well struck coins, especially Peace dollars, Franklins, Jefferson nickels and Ikes.

[LINCOLNMAN]

Just looked it up, no pics, mentions two 1795 1/2 cents, not 1797. 

[Conder101]

That's odd because 1797 C-1 half cents are well known overstruck on TAL tokens.  There is one in the Missouri cabinet. and four in the Davy collection, both sold by the Goldbergs.  The Missouri cabinet and one of the Davy coins  were single struck, three of the Davy coins were double struck over the TAL.

[BillJones]

On 6/27/2017 at 7:28 PM, allmine said:

Here's a Great One:

Found a 1797 C-1 1/2C overseas, a gorgeous Brown Fine double struck on a TAL, with TAL edge lettering on the Half Cent edge. Got all that? Sold it to a customer who insisted on having it PCGSed. Long story short, twice it was rejected as "Environmental Damage" even though it was as glossy and brown as a piece of caramel candy.  I called them up, asked them if they knew what the hell they were looking at, and their response to me as that no matter how nice and glossy and brown it looked, the undertype coin was porous so that's that, and it could/would never be graded Problem-Free

I learned many years ago that the graders at PCGS knew nothing about early copper at that time me. I lost all respect for their abilities after they gave body bags to a number of my pieces. The real kick in the shins came after I had sold a couple of pieces, and PCGS graded them, with straight grades for someone else. "Some pigs are more equal than other pigs" with PCGS grading. I will not submit coins to them for grading. They took my money and gave me nothing in return too many times for no reason. 

[kidrootbeer]

1 hour ago, BillJones said:

I learned many years ago that the graders at PCGS knew nothing about early copper at that time me. I lost all respect for their abilities after they gave body bags to a number of my pieces. The real kick in the shins came after I had sold a couple of pieces, and PCGS graded them, with straight grades for someone else. "Some pigs are more equal than other pigs" with PCGS grading. I will not submit coins to them for grading. They took my money and gave me nothing in return too many times for no reason. 

I find 'em as Useful I d i o t s, in that for the same reasons that you decry them, you can find plastic *bargains*

[LINCOLNMAN]

11 hours ago, Conder101 said:

That's odd because 1797 C-1 half cents are well known overstruck on TAL tokens.  There is one in the Missouri cabinet. and four in the Davy collection, both sold by the Goldbergs.  The Missouri cabinet and one of the Davy coins  were single struck, three of the Davy coins were double struck over the TAL.

Sorry if I mislead, QDB mentions 1797 as well as 1795, In the case of the 1795 he is more specific, naming two coins as well as their owners. He also says he knew of no 1796 examples. 

[numisport]

17 hours ago, Insider said:

This is not porosity.  The "dings" you are describing that are found on many coins are original planchet surface imperfections.  One numismatist named them "OPSI" marks in the 1970's.  Take a look at any planchet.  These marks are sometimes visible on well struck coins, especially Peace dollars, Franklins, Jefferson nickels and Ikes.

I owned a Pf 66 Cameo Lincoln that had round shaped 'pot marks' on the shoulder that didn't strike out. I assumed porosity but I don't have images of that coin. The coin I now own is a near perfect Pf 67 Cameo with no weakness in strike.

[BillJones]

<I find 'em as Useful I d i o t s, in that for the same reasons that you decry them, you can find plastic *bargains*>

I am too old to waste the time and money learning how to play the PCGS grading game. When it comes to early copper, I have can't figure out what they want. I see pieces in their holders with big problems, far bigger than any of the issues that my coins had. Yet I got shaft. Like I said, at PCGS you have to be an insider to get what you deserve or in some cases more than you deserve.

If I need to have a coin graded, I'll send it in via a dealer I trust. I've found that's the way to get fair treatment.

[kidrootbeer]

well, be that as it may, but the score for graded LgC so far is: 1 PCGS MS62RB became a MS65RB, 1 PCGS MS63BN became a MS67BN, 1 PCGS MS63BN became a MS65BN and the 1853 PCGS MS63RB should MS66 (it was one of the Billerica Large Cents), and that's just this year
Pre-1810 Half Cents: 1 NGC AU55 became an MS61
Never mind the Silver coins...

Some see grading Egress; I see Opportunities

[coinman1794]

On 6/24/2017 at 9:32 AM, LINCOLNMAN said:

As I move into colonials I encounter many details NG copper coins, due to corrosion. However, I see a number of coins with straight grades with seller descriptions that include "minor porosity" or "patches of porosity". Further, I see a number of early coppers that are straight graded that look no better (based on photos) than some of the details coins.

Is this one of those nebulous areas of "market acceptability"? Or, is there an objective test? Or, is it the case that in some instances it appears that the porous surfaces may have been there when struck, owing to an inferior planchet, and the coin is given the benefit of the doubt, being an early copper? 

Lastly, do the EAC folks see things differently corrosion-wise than the TPGs?

I think you answered your own question; this is "one of those nebulous areas of 'market acceptability.'"

Corrosion is a chemical reaction and porosity is a description of surface texture. They are often used interchangeably, for better or worse.