Help with coin

[Goldfinchs1]

I posted this on the coin forum too, but i thought it may be appropriate here too since the coin came from a shipwreck. Was diving some blackwater today and found a coin! First out of this area. The coin was found right beside some ships pattern pottery and beside a piece of "ironstone pottery" which I've discovered is from England and was primarily used in the early 1800s. I can tell that there is some kind of inscription on the coin but it's too dirty to tell. I know I shouldn't scrub it but would like some advice on cleaning. I don't even know what kind of metal it is, so I don't know what type of cleaning to attempt. My guess is silver. Please advise.
Thanks!

 

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[divewrecks]

Conserving marine archaeological silver coinage....

http://cool.conservation-us.org/byform/mailing-lists/cdl/2009/0117.html

Silver conservation....

http://nautarch.tamu.edu/crl/conservationmanual/File13.htm

Stan