Sunday, April 27, 2014

Checking die matches with Gimp

Recently I tried to compare the dies between an XF specimen and a damaged one. I mistakenly thought both dies matched, but actually only the obverses seem to match.

Let me explain how I use Gimp software to compare dies in the difficult cases.

First we need two coin images that are exactly the same size and rotation.

I use Gimp on the Mac. After opening the image I use the Measure Tool to check the number of pixels and the angle between two things. For example I will use the tips of the anchor.

If the angles I wrong I use the Rotate Tool to get the coin into a close orientation. Instead of eyeballing it I type in the difference in angles into the Rotate Tool's dialog box.

Then I use Image->Scale Image… to get the two images exactly equal in size. I haven't found an easy way to do this with Gimp; I use Gimp's percentage scaling and cross-multiplication. For example if one image has 330 pixels between two points, and other has 300 pixels I will do 330*100/300 to get the percentage.

Then I use Image->Canvas Size to increase one image. Next I select the other image, and Copy, and select the image with the large canvas, and Edit->Paste as New Layer. The New Layer part is very important. I get an image like this:

Then I go to the Layer, Channels, Paths, Undo window, and change the Mode from Normal to one of the merging ones, like "Grain merge."

If you aren't in the Rectangle Tool at this point enter it by clicking R on the keyboard. Then using the arrow keys walk the layer around until it is positioned precisely.

Then Save As. Choose a filename ending in .gif. Tell it to save the layers as animation with 1000ms between transitions.
Oops. Not a match. I had looked at undamaged places which were very close.
A match. Note especially all the snakes line up.

Hopefully you can see the obverses match and the reverses don't.

It is somewhat tricky with the obverses, because of the damage and the camera angle.

Photoshop software also has this ability, although I don't know the precise commands to work with layers in Photoshop.

Friday, April 25, 2014

Let's not forget to comment on the ancient Egyptian coins for the proposed MOU

Last week Peter Tompa suggested we should comment on a proposed emergency restrictions on the import of ancient Egyptian coins being considered by the US State Department.

I don't have much to say about Egyptian coins. I have three in my collection. I don't see a sudden surge of them in dealer inventories; but I haven't really looked.

These US-only MOUs are annoying. An example of my frustration: the picture below shows two ancient coins struck for the Greek city-state of Apollonia Pontika circa 400 BC. Around 630 AD the area was conquered by Bulgarians. The US signed a Memorandum creating import restrictions on material of Bulgarian origin in January, 2014.

What's unusual about the coins below is that the first is broken and has bits flaking off. It was sold openly on eBay Germany by a well-known long-time ancient coin dealer as a 'fourree', or silver-plated ancient counterfeit, in 2012. Yet the second coin seems to be struck properly in solid silver. It was also offered openly in an online German auction, but in March 2014, and without the paperwork to get the coin into the United States. So I declined to bid.

It certainly would have been interesting to bring those two coins together. It shouldn't be possible for the same dies to create both a fourree and a silver coin… Perhaps the first is not a fourree, but merely crystallized? Luckily I own the former, and now I'm incredibly curious to figure out what it really is. Yet what I really want is to have a chance to rejoin it with it's brother; a chance I almost had, but missed. The US stopped letting collectors import coins from Apollonia Pontika two months before this coin was offered. I will continue looking for an example with more documentation, but it can be difficult to find matches at all, let alone well-documented ones.

Egyptian coins from the Greek, Roman, and early Islamic periods are collected in the United States, yet also in Europe and in Arabia. If the US were joining a coin export ban popularly supported in Egypt and being implemented in other collecting countries it would be reasonable to support implementing it here. Having the US Customs go it alone without multinational support seems likely to have no effect on world collector markets nor on Egyptian archeology.

Read Peter's piece and if you agree follow his instructions.

UPDATE: added image in response to comment 1

Wednesday, April 09, 2014

WESPNEX coin show in Westchester County, NY

Last week there was a coin show in Westchester County, NY. The Westchester Stamp Coin and Paper Money show.

Over 30 coin dealers attend. US coins, foreign coins, even ancient coins. It's in White Plains, not far from the Metro-North train station. Easy access from the NYC area. They hold it three or four times a year.

There is nothing about this show on the Internet. No web site, no Facebook page, no listing on

It's not a bad show, if you can find it.