Metal Detecting

I've been asked to make a repost of a post I made a while back because it gets referred to often but it's hard to find which explains the density testing method for determining metal composition.

So here it is again.

Zero your scales and weigh the object you want to test, make a note of the weight. This ring weighed 3.91 grams.
Place a cup of water on a set of digital scales that are accurate to two or more decimal places. I'm using a Scobby Doo cup as it's the lightest one I have that clear so you can see whats going on, but something like a plastic cup from a coffee vending machine is lighter. Heavier glass cups will tip your scales over the . Reset to Zero, on my scales this is the Tare button.
Tie the object to piece of cotton of something similar, I’m actually using a bit of string that came off the netting that comes round oranges as it's very light and non absorbent. Suspended the object in the water, just below the surface so as little as possible of the string is added to the equation. Wait for the scales to settle and take the reading. In this case with the ring, it was 0.25 grams.
Simple Math

(Weight of the object) divided by (weight of water displaced)

In this case :- 3.91 / 0.25 = 15.64

Metal Density
Gold 19.3
Silver 10.5
Platinum 21.4
Palladium 12.0
Copper 9.0
9ct 10.9 to 12.7
14ct 12.9 to 14.6
18ct Yellow 15.2 to 15.9
18ct White 14.7 to 16.9
22ct 17.7 to 17.8
Sterling Silver 10.2 to 10.3
950 Platinum 20.1

18ct Gold, lovely ! This is a very reliable and easy method, no chemical testing which involes making a small mark/scratch.

Hope this is of use. Happy Hunting.

Thanks top bit of info

Here's the original thread, which also includes a slightly different method:
viewtopic.php?t=12854

Must say I think that is a great idea, will try that

Thanks for posting that, I will give it a try. All I need now is a scale. B-)

Very cool, all I need to find is some flaming gold.

Thanks for sharing that Barnet.....Very interesting & something I'll be using quite often(hopefully)!

Cheers

A

How the chuff does that work!!


Thanks, Im going to bookmark this!

That's a amazing test cheers

Neil and Julie,if I'm wrong but you can tell me lol but I think it started when an old scientist sat in a bath n wondered why the water rises,he then filled a measuring cylinder n added different object to the same amount of water and then come up with a mass equasion which would of evolved into this density equation lol I think that's right any how lol

"How does that work!?"

To work out the density of an object, you need to know two things about it: - the mass (Kg, grams, for example) and the volume (cm-cubed, cc, metres-cubed, etc). Then a simple division of mass by volume gives you density.
Example: Take a 10mm x 10mm x 10mm lump of lead. Volume is 1 cm-cubed (1 cc). On the scales, it will weigh 11 grams (typically). So density = 11 divide by 1 = 11 grams per cm-cubed.

Finding the weight of an object is easy, use some scales.

To find the volume - the method here uses bouyancy. When the ring is just submerged, it displaces (pushes out the way) a volume of water exactly equal to the rings' volume. There is less weight on the string , (say 3.7 grams instead of 4 grams)and an equal amount more weight on the scales (say 50.3 grams instead of 50 grams).
The convenient bit is this - water has a density of 1.00. So if the ring displaces 1 cm-cubed of water, it displaces 1 gram of water, which will be indicated on the scales as a 1 gram increase.

So.... as an example, if you have 50 grams of water in your cup, and you suspend the ring in it, you will have a weight of 50.3 grams (say). This means 0.3 cm-cubed of water has been displaced, by 0.3 cm-cubed of gold. And that's your rings' volume, = 0.3 cm cubed.

As scales aren't perfect, the other method I mentioned (in the link to the original post) may be a little more accurate. By weighing the ring with the cup of water in place, you are taking all three measurements at almost the same point in the scales' range, eg. 50 grams, 50.3 grams and 54 grams.
The original method takes the three measurements at 4 grams, 50 grams and 50.3 grams. The scales may behave slightly different at 4 grams to that at 50 grams.

In theory, you could obtain more accuracy by allowing for density changes of the water. Tap water has a slightly different density to that of pure water, and the density of water varies with temperature. However, if you look at how much difference these two factors make, it is really small, not worth bothering with whatsoever.

thanks for this information I will test it out with my jewellery later and hopefully find an object worth testing.

Hi,
this is a nugget of info ,we should have a page /cupboard were we can put this into,for library of reference?

Some clever poople on this forum

well done.

nugget11 wrote:Hi,
this is a nugget of info ,we should have a page /cupboard were we can put this into,for library of reference?

Hi, what we have done is in each sub forum anything that is for reference we have made the topic "Sticky" that means it always stays at the top, the topic is referenced with a light bulb symbol rather than a circle, have a look here

http://www.metaldetectingforum.co.uk/vi ... .php?f=120" onclick="window.open(this.href);return false;

Dave