Nic A Date Question

I'm not a chemist. Maybe biokemist6 will chime in.

Great information!

Let me start by saying I am a professional metallurgist and I acid etch hundreds of different alloys to examine their structure on a daily basis.

Here is a very nice powerpoint showing the microstructure of precious metals.

http://www.georgevandervoort.com/im...usMetals.pdf

Look at the picture on slide #17. The interior has a uniform, equaixed grain structure indicating an annealed, recrystallized structure. This is similar to the structure of a planchet before being struck by a die. On the surface where the sample was sheared, you can see a change in structure and flow lines from where the material was deformed and this has a certain depth before the sample returns to the "normal" equaixed structure. Similar changes in structure result when a die strikes a coin. When you acid etch a coin, you are revealing the microstructure because the acid preferentially attacks higher energy areas such as grain boundaries and that changes the way light reflects off the surface. Macroscopically, the date is revealed due to a visible change in structure. Even after a date has been worn away, there is still a change in the structure caused by the low points being more cold worked and plastically deformed by the die compared to the high points.

So you're right by saying "even when the actual metal at the high-points has been worn away, the crystalline structure of the metal surface at the two points remains different", but not exactly right by saying "different rates of dissolution cause a perceivable difference in height between the two areas." It's simply a matter of being able to perceive the different crystalline structures on a macroscopic scale.

Also, you can acid etch silver, gold, copper, nickel and any other metal or alloy. You just have to find the appropriate etchant for each alloy. I believe nic a date uses ferric chloride. According to the powerpoint, a solution of 10% sodium cyanide and 10% ammonium persulfate was used to etch fine silver and a solution of ammonium hydroxide and hydrogen peroxide was used to etch sterling silver. I doubt you will be able to find a product to etch silver outside of a chemical lab.

Always happy to be corrected by a master.


I wonder what the optimal etchant for coin silver (.900 fine) is, then. I recall one thread where a new member posted that they recalled long ago some chemical that used to be marketed as "Silver Date-Back" that claimed to restore dates on badly worn silver coins, but that it was no longer available. I was assuming it was either some kind of scam or an urban legend, but if what you say is true then it could well have existed, but was pulled from the shelves due to the hazardous nature of the components. Especially if it contained cyanide.