Classical Numismatics Discussion
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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Coin Photography, Conservation and Storage  |  Topic: Special technical evidence 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Special technical evidence  (Read 1498 times)
slokind
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« on: January 09, 2007, 12:57:19 pm »

Since this hasn't to do with conservation or fakery or storage, or with any special tecnniques in photography (it is just a detail from an acquisition photo), I would like to see a strictly limited thread in Classical Numismatics for this kind of thing (such as we have, e.g., for Mythology), but I do not have the right to initiate one.
So.
Here is a detail from a wonderful new acquisition, which I'll wait to discuss elsewhere in terms of die linkage.  This is for what it shows.  We see not only the original 'centering dimple' but (a) across the cheek, an ancient scratch that the patina fills, (b recent chips in the 'Danubian' patina, and (c) a very recent gouge showing the Moesian brass looking just like the true orichalcum that I suspect that it is--at a date when it is hardly seen looking this pure at the Rome mint.
Even in an image limited to a 5MP one-piece camera, the thickness and the layers of this kind of patina can be studied, and this is a very well preserved patina of a lovely color (on the reverse, most of it is gone, but not so recently).  Also, it reminds us how much sharpness in the die and strike this lovely kind of patina can obscure.
Pat L.
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bruce61813
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« Reply #1 on: January 10, 2007, 11:28:29 am »

Thank you Pat, to everyone, the objective of Pat's post is to illustrate technical details. Please avoid general comment, but post specific detailed illustrations. This is intended to become a learning tool for all of us.

Bruce
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moonmoth
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« Reply #2 on: January 12, 2007, 01:54:30 am »

I have a page of colourful patinas that might be of interest.

http://www.forumancientcoins.com/moonmoth/patina_coins.html
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slokind
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« Reply #3 on: January 12, 2007, 03:09:05 pm »

By zooming your picture of the whole coin, one sees that the Deultum for Diadumenian with Asklepios and Hygieia shows still more: someone has tried to "liberate" more detail by damaging the patina.  This thick patina can be frustrating, but with strong light one can usually read the legends through it, provided the surface hasn't also been waxed or varnished or 'smoothed' by pressure (causing more complicated light difraction).  I liked the one I used because it has no modern human damage, exceptionally nowadays.
But what I'd really like to know is why coins found along the Danube and on the north coast near by of Asia Minor (read Bithynia), the patina is so like (as you say) a ceramic glaze that it also can develope, naturally, the same kind of craquelure as, for example, lead-glazed pottery.  And you have it on two from different mints.  Freezing, seasonally?  It has to come from differing coefficients of expansion and contraction? 
Which mint, though, did your Constantinopolis Commemorative come from?  These are, one reads, basically just copper rather than brass or bronze (other than zinc-alloyed) coins.  Pat L.
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moonmoth
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« Reply #4 on: January 13, 2007, 06:41:40 am »

I suspect that someone who knows the mint styles might be able to give the mint for the Constantinopolis coin.  In the hand, the crackle effect on that one seems to be on the surface, and it shows clearly with normal illumination.

The patina on the Diadumenian coin is thicker and glassier, which may be why the effect seems to be deeper on that one.  A flash photo penetrates and brings out the crackling; the photo taken with a lamp as a light source shows the surface, which appears plainer, and quite dark unless the light is bright.

It does annoy me when people scrape away at a perfectly good surface!  My other coin with the same reverse die has been horribly gouged by an idiot (luckily, not over the whole surface).  That one has a very different patina, much more delicate, with a light and sandy appearance.  In fact there are sand grains embedded on the surface.

For the benefit of the thread I will show a couple of photos here of those two patinas on Deultum coins with the same reverse die.  The first is a flash closeup of the thick green patina.  The second is the sandy one, illuminated with a lamp. You can see the sand grains in Asklepios' moustache.
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"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."
slokind
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« Reply #5 on: January 14, 2007, 02:53:53 pm »

This article is much more than its modest title might promise.  Make sure you scroll through all of it.  Pat L.
http://www.forumancientcoins.com/moonmoth/crystal_coins.html
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