Chemical problem

[amena]

Hi all.
I would like to submit you this problem.
Some times it happens that when I place a drop of reagent (dichromate based) on the surface of the object to be tested, I get no reaction, as if the object were made ​​of metal.
However, if again I place a drop of reagent in the same spot, I get the red reaction, as if the object were made of sterling silver.
I tried to explain this fact thinking that the object is made of a low silver content alloy. Perhaps the first drop melts the base metal, so the second one reacts at a higher silver content.
I do not know if this is the correct explanation of this phenomenon, and I would like to know the opinion of someone who knows more than me about chemistry.
Thanks in advance
Amena

[amena]

Since no one has replied, I reluctantly approached the density test on one of those pieces that showed the phenomenon that I mentioned above.
I hope everyone will refrain from telling me it's an easy test.
I'm not very skilled at measuring the weight and I have made ​​several weighings getting slightly different results. The corresponding silver content is between 20 and 30 percent, unless errors.
This could confirm my explanation.

[dognose]

Hi Amena,

I would have agreed with you're first findings, but not that the acid was burning away the base metal, but burning away the deposit of polish, grime, etc. that builds up on such items after many years of handling. As the acid eats through this matter, it loses its power and gives no positive reaction, but has left the area clean and exposed the original surface of the silver, and thus when fresh acid is applied it now gives off the red reaction.

I stumped as to why someone would make such an item with just 20-30% per silver. I'm unaware of how low the silver content of an item can go before it loses the colouring of silver, but assume to get the colour of your item that it must be mixed with another white metal. If that is the fact, then why use silver at all?

Trev.

[amena]

Actually the cigarette case appears dark and dull when compared to a sterling silver one.
However, even if you scratch the surface with sandpaper, the first drop does not give the red reaction .
It is certain that there is some silver, otherwise the red reaction would not take place.
I was also amazed that something so engraved was made of so low silver alloy, but maybe labor was very cheap in some countries . I believe that the object is Persian or from some neighboring country.
I enclose a photo of the back


Best wishes
Amena

[JLDoggett]

I agree, stylistically it looks to be Persian or from that general area. It is odd to be so low in silver content. Below 40% pure, silver starts looking brassy unless the alloy is heavy in nickle and this would affect your chemical reactions colour. If you have you washed (not polished) the item it should react with the first try. It is hard to believe that that much work would have been done on a very base metal.

[amena]

I ran the density tests on a tribal bracelet that showed about the same phenomenon that I described above.
This time I think I've got a more accurate result, because the object is smaller and smooth
Weight in air 90.02; weight in water 80.6: Density 9,556
This corresponds to about 40% of silver in the alloy.
Amena