"Granular Surfaces" versus "Porosity"

[Britannicus]

What is the difference between a coin described as having "granular surfaces" versus a coin described as having "porosity?" It seems to me that porosity would give a "granular" appearance to a coin's surface. At least that is what I have observed.

Are these just two different ways of describing the same condition? Is it a matter of whether the cataloguer chooses to describe the cause or the effect, such that porosity is the cause, and granularity is the effect?

[Joe Sermarini]

Porosity describes a surface with many tiny holes, microscopic pitting, like skin pores. 

Granularity describes a surface with crystalline grainy roughness.

Some cataloguers may use them interchangeably but they should not.

[Britannicus]

Joe, I understand that you are clearly describing two distinct conditions, and it makes sense to me.

Would a surface with a crystalline texture, which might be described as granular, be brittle and crumble easily?

Also, I wonder if there are magnified images somewhere that would show a side-by-side comparison of granularity versus porosity.

[John Anthony]

This is a coin that I would describe as having a granular surface. If I'm wrong, please correct me. The coin isn't "crumbly" in the least - it just has rough surfaces.

[Joe Sermarini]

Would a surface with a crystalline texture, which might be described as granular, be brittle and crumble easily?

Bronze is never actually crystallized only crystalline and granular in surface appearance. A bronze coin will not be brittle and crumble easily.

A silver coin that is granular can be brittle and can be fragile, but "crumble easily" is not likely.

[Joe Sermarini]

This is a coin that I would describe as having a granular surface. If I'm wrong, please correct me. The coin isn't "crumbly" in the least - it just has rough surfaces.

I would describe that coin as porous. It appears to be covered with tiny pits. I do not see it as granular at all.

[Molinari]

These are helpful, and I'm trying to make numiswiki entries for both, based on Joe's description, but it doesn't seem to be working!  I edit the "new" page, which it says I can create by clicking the "create a new page" option.  When I entered the text for "Granularity" and saved it, the word was not blue in this thread.  How come?

Nick

[Joe Sermarini]

The links are not created instantly, but are generated by a program that runs once a day (or I can run anytime and I just did).

[John Anthony]

For the sake of comparison, can you post a coin you would consider granular?

[Taras]

I'd say this is an example of granular surface...

[Callimachus]

Here is a bronze coin of Julian with minor porosity, especially on the obverse.
(Click on the picture to make it larger.)

[John Anthony]

Much appreciated, thank you.

[Joe Sermarini]

Grainy...

[Joe Sermarini]

Porous...

[Joe Sermarini]

A coin can be both grainy and porous. Sometimes, it is difficult to determine which term is most appropriate. Although I do think they are different conditions, I don't think getting it wrong is a big deal.

[joejitsumd]

What is the difference in appearance between porous and cast bubbles?

[Joe Sermarini]

For porous, look at the photos above. For casting bubbles, look at examples in the signs of casting examples on the fake coin reports.

[dougsmit]

I also apply the term 'granular' to coins with finely speckled/scattered patina or deposits above the original surface as on the Magnentius below while reserving 'porous' for coins eroded finely below the original surface as on the Trajan below.  In both cases the fault is fine rather than coarse when we would change to words like encrusted and corroded or just the catch-all 'rough' demonstrated below by the Caligula.   These days we see the terms used for more and more severe surface irregularities.  Coins like the reverse of this  Titus with corrosion removed surgically are not just rough.  They are what they are.  We each will differ where we draw the like between collectible and to be avoided but we should avoid using weak words to hide the ugly truth.

[Britannicus]

"Pitted" would appropriately describe the Caligula and Vespasian.

[Joe Sermarini]

I agree. Perhaps "smoothed pitting" for the Vespasian, but even that is not entirely satisfying. Perhaps someone else can do better (keeping in mind the reasonably limited number of words a dealer would want to use). 

[SC]

If I was selling them I would say "extensively pitted" for the Caligula and "natural pitting with some smoothing on the reverse" for the Vespasian.  Wordy for the latter but I would want to contrast that fact that its condition is part natural effect and part man-made. 

Shawn