can anyone tell me about this sgain dubh

[Grizzly]

As far as I know any method of cleaning silver always removes a tiny bit, here's a link on how to clean it. - http://m.wikihow.com/Clean-Silver

The rampant lion is a Glasgow Mark, it's also indicative of being sterling silver, i.e 925 parts out of a 1000 is pure silver.

Henry Tatton was an Edinburgh silversmith, it just means the piece may have been assayed in Glasgow.

Hope this helps.