Yesterday, I described how I had a suspiciously good price on a silver coin via eBay. Now, there is a chance that I was lucky and got an auction on a real coin where for whatever reason, the price didn't reach expectation... or more likely, I was scammed with a fake coin!

I also had a number of other coins that I had bought via eBay or Marktplaats which I wanted to test a bit further with the specific gravity test. All these coins had passed the magnetic test, the magnetic slide test and also the ping test already, so I wanted another non-destructive test that I could do at home to put my mind at ease.

From left to right in the featured photo above: the coins are 2018 Weiner Philharmonic coin (bought from a reputable dealer, so I trust this one!), a suspect Mongolian Gilded Mouse Coin (from eBay) and the suspect 2019 Wiener Philharmonic coin from the previous post

Just for a quick run down of the other tests (which I've learnt about in the previous months thanks to helpful members of the Hive account@ssg-community!):

Magnetic test: Pure silver is non-magnetic, so it should not stick at all to a strong magnet.
Magnetic slide: Pure silver is diamagnetic, so a small strong magnet should slide down it's tilted surface slower than free fall.
Ping test: There is a certain ring to the silver if you take another coin and tap it (whilst it is allowed to freely vibrate!).

Specific Gravity

The specific gravity test is described really well on this non-Steem webpage. Specific gravity is defined as the ratio between the density of an object and the density of a reference substance that it is immersed in. In practice, it becomes easiest to measure it as the ratio of the weight of the object outside the substance over the weight of the object immersed in the substance. In our case, it is silver (the object) and distilled water (the substance).

The tools

The required tools apart from the coins themselves are:

• sensitive scale (readings to 0.01g)
• something to tie the coin with (I started with fishing line, but I discovered a better trick!)
• a lightweight cup that can hold enough water to immerse the coin
• distilled water

Method

I'm just going to run down the method quickly for a single run of the good 2018 Wiener Philharmonic coin. I was practicing with this good coin so that I would know if I was doing something wrong if the numbers didn't come out right! Take note, I did several runs for each coin and measurements were taken a few times just to be sure... not a completely scientifically secure test, but a decent one. Remember, this is for peace of mind rather than the discovery of a new physics at the LHC....

First, you need to get the "dry" weight of the coin. So, the 2018 coin measured in at 31.14 grams... this was confirmed with a few measurements.

Next you will need the submerged weight of the coin. So, you just fill your cup with enough water to immerse the coin and pop it on the scale. Then you tare the scale (make this the new zero)... and tie up your coin on a string and pop it in.... making sure that you DON'T touch the sides or the bottom of the container, as you want to measure the displaced fluid and not the actual weight of the coin.

Ahem... yes... tying up the coin... On every guide, they just say... tie the coin with a string or a sewing thread. Have you TRIED to tie a coin? Try it, you are in for a world of pain and frustration! Even Googling the question led nowhere... I now know that it doesn't work to drop coins on a string into a modern vending machine and I have gotten familiar with the decorative COIN KNOT!

However, even in the vending machine tricks... they start with. Tie your coin to a string...

... so I started thinking of a lateral way around this!

Every morning, I tie up my youngest daughter's hair with this little elastic bands for toddler and baby hair. This is mostly to keep it out of her eyes, and also to try and keep food out of it (it doesn't work for the second part...). They are super thin and light, and more importantly... they wrap around a coin!

Problem solved! I have "tied" the coin with a piece of sewing thread.... and a light elastic band.

It doesn't take up much volume and it weighs very little (0.04 grams)... so I hope it doesn't distort the results too much.

Ta Da! Lateral thinking for the win!

So, the "wet" immersed weight of the coin!

Results

So, with each coin measured several times (and each measurement done a couple of times). I have these rough and ready results to compare against the "pure silver" result which should be 10.50:

2018 Wiener Philharmonic 1 ounce silver coin
Dry = 31.14 grams
Wet = 2.97 grams
Ratio = 10.44

Gilded Mongolian Mouse 1 ounce silver coin
Dry = 31.13 grams
Wet = 2.98 grams
Ratio = 10.45

2019 Wiener Philharmonic 1 ounce silver coin
Dry = 31.20 grams
Wet = 2.99 grams
Ratio = 10.43

It appears that the two suspect coins are decent enough to have passed this test! They both ended up being very close to the real 2018 silver coin, and so that is good enough for me. I still wonder a bit about the Mouse coin though... I would have thought that the gilding would alter the result a touch more... but maybe not?

I have forgone any error analysis and all of that important stuff... mostly, as this was a rough experiment to verify in my mind the coins. Of course, this could be done much more robustly!... but for now, it appears that these two coins are okay... I have a few more to test...

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