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 Post subject: How do I test for silver?
PostPosted: Wed Nov 10, 2010 5:50 pm 
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Location: Moncton, Canada
Hi all,

Someone has offered me an approximately 1 lb piece of what he believes is silver. He says it came from his grandfather's blacksmith shop.

Silver? In a blacksmith shop? Really?

Is there a specific way (perhaps some acid reaction??) that will tell fairly conclusively whether the piece is or is not silver? I'm thinking of filing off the surface, in case it's plated, then brushing on a uniform coating of sulphur & heating, then comparing with a similarly treated piece of known silver. If it should be sterling, apart from green color in flame, is there another qualitative way of testing for copper content?

Cheers
Hans Durstling
Moncton, Canada

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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 10, 2010 6:35 pm 
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hi Hans

Quote:
Wolf the general method is to use the silver test solution by applying a drop to a groove filed in the metal. Then look at the color of the solution and apply the following principles:

Bright Red: Fine Silver
Dark Red: 925 Silver
Brown : 800 Silver
Green : 500 Silver
Yellow: Lead or Tin
Brown : Copper
Dk Brown: Brass
Blue: Nickel

As a side note, make sure the piece is CLEAN.

If you don't have red top or nitric acid handy, we also use the following method and this is from a set of instructions I have posted:

BTW, a smoothly sanded stone is ESSENTIAL for this test.

Rub the unknown white metal on the stone. Apply 18K acid to the streak and note the reaction.

If test mark turns to intense silvery blue color, there is strong silver content.

If test mark turns to a blotchy uneven blue color it is silver plate.

If it dissolves completely it has no silver content.

Even silver coins that are just 10% pure will leave some faint blue streaks or faint blobs. A false silver reading may be obtained if the item being tested is very heavy silver plate or a Sheffield (silver filled) process.

DESTRUCTIVE SILVER TESTS:

Take a file or knife to a smooth flat area of item being tested. Go as deep as possible depending upon the value of the item being tested and the circumstances. Then drop 14K acid on the spot.

If the metal is 90% or higher the spot will turn a whitish milky gray color, it will likely be.925 sterling silver.

The whiter the color, the higher the silver content.

If the spot turns a noticeably darker gray color the silver is approximately 80%.

The darker the color the lower the silver content.

If the silver is below 60% green bubbles will form.

If the bubbles are immediate and very green and profuse the item is not solid silver. Silver below 50% is seldom encountered in jewelry or silverware.

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This was Mcgyvers post on the subject couldn't find it in the forums so had to take it out of the documents section of my puter

hope this helps

wolf

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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 10, 2010 7:59 pm 
It's good sized sample and therefore a good SG determination by the hydrostatic method (weighing in air and in water) should give an accurate result if you have, or can access, suitable scales that can handle the weight.

Seeing that it's a family hand-me-down, its unlikely to be an outright scam (say > 50% by volume a base metal buried within the bar). If it is, the SG check should detect easily if it's a little silver covering a lump of base metal.

More probable from an old blacksmith's forge is that it might be cast from some alloy rather than being pure silver. Here you might want to go directly for an assay by one of several methods. However, given the size of the bar and having ruled a silver covering of a base metal, consider the following:

- Since you don't own the bar, the owner might not take too kindly to you carrrying out (multiple?) tests yourself that cause visible damage to his 'treasure'.
- That said, at yesterday's price, if it is silver bullion, its value is only about USD 540. Were it to assay at (say) 92.5% silver, the price differential is going to be something like 7.5% of that (or about USD 40.
- If (quite possible), its a casting of melted silver coinage, the silver %age is likely to be about 80-83% (80% in the case of Canadian silver currency). This could raise your exposure to a risk of loss to about USD 90.
- How much are you prepared to spend (in time, equipment or by fee) to avoid a possible loss of USD 90? If it was me, I'd explain the position to the owner, offer 80% of the bullion value and have done :D


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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 10, 2010 8:20 pm 
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True but I also enjoy kitchen table chemistry and improvising solutions; in other words re-inventing the wheel for the fun of it. Spec G is doable but would entail building a saddle for the scale; I have nitric (conc), 38o HCl and can get suphuric acid but don't have any specially formulated 14k and 18k acids.

The owner is actually quite cavalier about it, in his eyes it's more of a lump than an heirloom. He may want something made with it, but it seems mainly he's curious.

Cheers
Hans

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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 10, 2010 8:54 pm 
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Hans,
Shor Inc. sells silver-testing acid here: http://www.shorinternational.com/TestGold.php

I don't know how tough it will be to import it to Canada but they should be able to tell you. Similar products are no doubt available there as well, and maybe Shore has a Canadian affiliate.

Brepohl gives the formula for silver testing acid as: 3 g. potassium dichromate; 3 ml. concentrated sulphuric acid; 32 ml. distilled water. EDIT: for those who don't know, ALWAYS ADD ACID TO THE WATER, NOT THE REVERSE, FOR SAFETY REASONS!

The workpiece is scratched with a file and a drop of the acid is placed on the scratch. If silver is present the testing acid will turn the brownish-red acid to a blood red color. It won't tell you how much silver is in the alloy and it won't work if there's less than 25% silver.

You can also use concentrated nitric acid, table salt and a touchstone. Make a streak on the touchstone with the sample and put a drop of nitric on it. When table salt is added a milky color will develop if silver's present.

Hope you're able to acquire a nice lump. Silver prices are skyrocketing!

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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 10, 2010 11:04 pm 
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Thanks for the info Rick; as I said, half the fun for me is improvising kitchen table tests, so I'm not likely to buy a test kit; specially when it's only a single lump, talked about on the phone and not yet seen. I'll try the nitric and table salt combo for sure - if the guy and his lump ever actually do show up. You know how it is with these telephone queries.

Cheers
Hans

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 Post subject: Re: How do I test for silver?
PostPosted: Mon Nov 15, 2010 12:50 am 
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Take a piece of it, weigh it accurately, and dissolve it in Nitric acid.

Then using an eye dropper drop Hydrochloric Acid (or table salt but since you have the acid I would use that)into the Silver Nitrate solution that is thus obtained. If it is silver the silver will precipitate out as grayish white powdery looking precipitate. AgCl, silver chloride.

If you want to get really fancy weigh the piece accurately before you dissolve it.
Then add HCl until there is no further precipitate. Then neutralize the supernatant liquid with baking soda or lye. Then filter the precipitate onto filter paper (a coffee filter preweighed while dry will do just fine. Maybe two thicknesses) rinse with DI water and dry really dry. Weigh the silver chloride and calculate how much silver is there from the formula weight.

If you actually do this I will look up the formula weights for you and help you with the calculations.


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 Post subject: Re: How do I test for silver?
PostPosted: Tue Nov 16, 2010 6:46 pm 
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Thanks G4 - I like the suggestion. It's been years since I did anything quantitative in the wet way (or in any other way for that matter). I'll likely take a kick at it in the next week or so if the guy with the lump of (putative) silver actually does follow through. So far it's been an initial phone enquiry only.

Cheers
Hans

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 Post subject: Re: How do I test for silver?
PostPosted: Wed Nov 17, 2010 8:15 pm 
Hans Durstling wrote:
Thanks G4 - I like the suggestion. It's been years since I did anything quantitative in the wet way (or in any other way for that matter). I'll likely take a kick at it in the next week or so if the guy with the lump of (putative) silver actually does follow through. So far it's been an initial phone enquiry only.

Cheers
Hans


Do let us know what it comes out at. In a betting mode, I'd bet it is (mainly) silver and close to 800/1000 or (much less Likely) 1000/1000.

When the 'developed' nations came off the gold Standard for their currencies after WWI, a lot 'small' people lost a lot of money. Gold coin they had banked, they could not withdraw and were offered paper instead. When they then tried to use the paper to purchase gold coin, they found that they were subject to a massive, covert, devaluation govt scam!

People learned their lesson! UK stopped minting silve coinage in WWII (annd withhdrew substanntially existing coins from circulation, to ship the silver to the US, part for payment of old lend/lease WWI destroyers and part to equip the Manhattan Project. The Dominion of Canada, however, kept minting silver coinage (.800) until 1967. After that, only fools would continue to have circulated their silver coins and should have sorted to the local blacksmith's forge to render them to ingots against a rainy day :-)


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 Post subject: Re: How do I test for silver?
PostPosted: Fri Nov 19, 2010 1:22 am 
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Thanks. That strikes me as a plausible scenario to account for the presence of silver in a blacksmith shop. The chap whose has the stuff has not called back yet, so the story may well end there. But if the lump does materialize, I will certainly do the HNO3 procedure and keep everyone posted as to the outcome.

Cheers all,
Hans Durstling
Moncton, Canada

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