Tuesday, March 07, 2017

Video on creating 'coins' with CNC machine

I stumbled across this 9 minute video which shows the process of creating a medallion with realistic bust using a CNC machine.

The medallion produced looks quite good! It looks better than most of the 'coins' featured in do-it-yourself coin making videos. Yet most of the steps made me cringe because I was certain he was doing it the wrong way.

Once he has a 3D model on the computer, he feeds a block of metal to a CNC machine rated only for wood. I was sure something would go wrong but he got it perfect.

To produce the round shape he just takes his metal block and starts hitting it with a belt sander! I was certain he was doomed but it looked very nice when complete.

To give the appearance of patina he uses spray paint. I was amazed that this worked at all! He got a nice effect in the end.

The final medallion suffered a bit of a 'staircase effect' on the face due to the limited depth control. I would have liked to see if he could have removed that with a bit of polishing. Even with the depth artifacts he managed to produce a pretty nice medallion using techniques I would not have expected to be effective.

Saturday, February 25, 2017

Print on demand catalog of the coins of Troas

I recently purchased a Print on Demand copy of Warwick Wroths 1894 catalog of the British Museum collection Catalogue of the Greek Coins of Troas, Aeolis, and Lesbos.

Google scanned three copies of this book: from the University of Michigan, from the New York Public Library, and from Harvard

The Harvard copy doesn’t seem to show up in an ordinary Google Book search. I found it using this link: http://fig.lib.harvard.edu/fig/?bib=002349380.

Public domain books that have been scanned by Google can be printed on demand. To order online, just bring up the book in Google Books, click “Get this book in print” and “On Demand Books” and several vendors appear. I wanted to see an Espresso Book Machine in action. There is one at the McNally Jackson bookstore in Manhattan. So I went down there, armed with the title.

The machines aren’t self serve. I gave the operator my title, and he brought up the University of Michigan Copy. I had hoped to see it printed but the machine apparently takes a while to download the book. It downloaded overnight and the operator printed it the next morning. I was surprised to find I had received Harvard’s copy.

The problem with getting a different copy than expected is that Google’s 2008-9 analysis did a poor job of distinguishing photo plates from line art. For numismatic books this is a problem. If the Google book preview shows a coin “posterized” the print on demand copies print it as a black blob. Luckily Harvard's copy is better than the U of M's.

Here are three copies of plate 8. On Harvard and the NYPL’s copy, coins #1, #2, #18, #19 and the reverse of #22 are shown greyscale. On the U of M’s copy, none of the coins are shown greyscale. They all appear as “posterized” four color art.

The “posterized” coins appear as black blobs when the Book Machine prints them. I am not certain this is the fault of the book machine. It is unfortunate that there is no way to supply feedback to Google books that a page or part of a page is greyscale artwork.

There is also no way to specify that the printed size of the page is meaningful. This is not a huge problem for the BMC volumes, which originally appeared the similar in size to what the Espresso Book Machine prints.

I paid $17 plus tax for this volume. For comparison, the hardcover decent plate Italian edition by Forni from the 1960s can be found used for $50, with other copies selling for more. The original version can sometimes be found at auction for $150+.

Many years ago I wanted to get folks with original BMC volumes to scan the plates. I had hoped to assemble a plates-only PDF. I managed to scan a few volumes myself but was not able to get the needed volumes and the project fell through. Perhaps with the British Museum putting their collection online the need for this has passed?

Thursday, January 19, 2017

ISEGRIM search form

ISEGRIM is a database of 60,000 Greek coins of Asia Minor developed by Otfried v. Vacano at the University in Düsseldorf. There are no pictures. Unlike other search sites, instead of filling out forms the user was to write "queries" using a special syntax similar to Lucene. Although powerful, it has been difficult for computer novices to use.

I created a proof-of-concept for searching ISEGRIM using forms. My experimental site is at http://isegrim.mybluemix.net. If you already know ISEGRIM this site still gives one advantage because it alters search responses to the BMC Greek catalogs to be hyperlinks. So if you are in the United States you can just click to go to the BMC description (then search for the plate, if any).

I sent an email to the ISEGRIM contact address but got no response. It is possible they will ask me to take it down. Or maybe they will let me contribute it to their site.

This is a proof of concept. Let me know if it helps.

Wednesday, December 28, 2016

Odd surface on presumably fake coin

I show here two coins from the same die pair. The high grade example is a Bulgarian replica of a Neapolis stater. The damaged example was sold as genuine on eBay this spring.

This replica shows up being offered from time to time as genuine. This new example surprised me because the damage is so strange. Here is a close-up:

Several things are going on. Pieces are broken off! There is strange cracking that follows the shape of the gorgoneion. There is a lot of wear both normal and strange looking.

Has anyone else seen a coin with this coin of surface?

Friday, December 23, 2016

3D model of Kushan coin

The Institute of Archaeology of the University of Warsaw has provided a remarkable 3d scan of a Kushan bronze coin. The model was done by Otto Bagi and Sergi Mañas Jolis. Apparently photogrammetry was used to to infer the 3D coordinates.

I am inquiring what kind of equipment and software is needed to produce such models.

The team also has a nice model of an Alexander tetradrachm and a cupped Byzantine coin. All the models can be rotated and zoomed with your mouse or trackpad.

Wednesday, November 16, 2016

Is this 'panther' Cerberus?


Numismatic Naumann, auction 46, lot 182

Medusa is not the only creature in Greek mythology with snakes for hair. The monstrous dog Cerberus, who fought Herakles, had a mane of snakes.

Coin depictions of Cerberus (electrum hekte, Italian bronze, Roman aureus) show the monster with two or three heads but no snakes. Vases often show snakes.

There is an animal with snakes in its mane on a very rare Greek coin. This diobol (weight 1.08g, 11mm diameter) seems to depict an animal with a mane of snakes on the reverse. The animal has whiskers and triangular ears. The coin is rare; I have only been able to locate two other examples.

CNG e-334, lot 157
CNG 73, lot 419, no snakes

I suspect that this coin reverse depicts the head of Cerberus. In addition to the snakes, the ears resemble the ears of Cerberus on vase paintings. Some dogs have whiskers, and some Greek and Roman art shows Cerberus with a at least one lion head. Thus, none of the features rules out Cerebus. In addition, Cerberus is not always depicted with multiple heads.

The reverse is thus not a generic panther or lion as suggested by the catalogers of the coin example, but a rare depiction of Cerebus with a mane of snakes.