Strange marks appear from nowhere:

Hello everyone,
I have been buying and selling Silver, in a very small way for some time.
I have come across this half sized Silver hip flask that has me stumped.
It was really dirty when I bought it off ebay so I gave it a good clean using a radial wheel in a dremel, very lowest grade, all was well.
When I went to clean it further, getting rid of scratches etc on my lathe, problems started.
As soon as it started to get hot these marks started to appear.
I have seen this only once before, on another flask funny enough, it turned out the other flask was Silver plate but this one is hallmarked, very badly faded but hallmarks.
I am hoping someone could tell me what these marks are, they spread when hot and they will not come off.
Thanks so much.
flask-2.jpg
flask-1.jpg

Looks like an English silver hallmark, almost certainly a London assay mark from either the 1896-1925 or 1926-1945 cycle. From the shape of the punch the maker may possibly be Goldsmiths & Silversmiths Co Ltd.

Hi,
Thanks for the reply.
I must not have worded my question correctly.
I am not asking about the hallmarks I am asking about the marks on the body of the flask, in the picture, what they are, if it is indeed Sterling Silver the marks should not be there?
Thanks.

That mark may be where a monogram or engraving has been erased and/or filled in.

Billym,

You shouldn’t have used a Dremel to polish this piece because it revealed the firestain – hermansilver.com/glossary.htm#Firestain. The only way to remove it is by copper depleting the flask’s surface or polishing out the firestain on entire flask.

I can’t say this in strong enough terms: NEVER use a Dremel to polish silver unless you’ve been trained to do so. When in doubt, contact a silver restorer.