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  #21  
Old 04-04-2017, 07:52 PM
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ToddB64 ToddB64 is offline
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Default Testing Jewelry Value Before Selling.

Hi !

I'm looking for serious replies to help me understand something on this one please.

Besides needing help as mentioned in my post at the bottom, my intent is to offer information I have found on the Internet that might be helpful to anyone interested in doing advanced tests to determine the value of their Jewelry before selling. This goes beyond tests such as using neodymium magnets, acids and simple tests just meant to get a general idea of what a material might be.

However, before addressing my post at the bottom, I need to present an explanation regarding the difference between Density and Specific Gravity of materials. The URL where these points were found is listed at the end of this paragraph in case you want to read the entire document. However, for the sake of brevity, I'll just reiterate some of the main points that should be helpful before we go further. http://www.tekra.com/sites/default/f...%20Gravity.pdf

Main points from the above tekra.com URL:

Density and Specific Gravity are both ways of describing the weight (mass) of a certain quantity of material. They are useful in determining yield and comparing different materials.

SO WHAT'S THE DIFFERENCE ? NOT MUCH. The main difference is that density has units and specific gravity does not. Why not ? Specific gravity is determined by dividing the density of a material by the density of an equal volume of water using the same units. The units therefore cancel each other out. This means you don't have to worry about conversions when comparing materials that have densities using different units.The specific gravity value of any given material is going to be the same in the US, Germany or China ! (Also, materials with a specific gravity of less than 1 will float on water.)

Fortunately, there is a loophole in the "no units" rule for specific gravity. It just so happens that the density of water in grams per cubic centimeter (g/cc) is very close to 1 (0.9976). This means that the specific gravity of a material is virtually the same as it's density in g/cc. Material density g/cc ¸ 1 g/cc = material density = specific gravity.

So, with the above out of the way, we can go forward to my post below, understanding that using the results of a Specific Gravity test in water actually gives us the Density of the item tested and then comparing that test result to the closest density reading found in the Density column of a Periodic Table, is a valid method to determine the type of element tested, or the Karate of a gold ring.
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MY POST FOLLOWS:

https://www.youtube.com/watch?v=vYkfIAk8AMI ←[U]How to Test Gold Using Specific Gravity YouTube by Chad

I saved the above YouTube in the Favorites list on my computer and have watched it several times. In the second part of the video Chad has a bowl of water sitting on his digital scale and presses the Tare button to zero out the weight reading. Next, he suspends his gold ring tied to a string down in the water, making sure the ring doesn't touch the sides or bottom of the plastic bowl and then records the weight as only 0.3grams after taking a dry weight reading for the ring of 3.5grams. This part of the video has me baffled. I'll try to explain in the next paragraph.

To begin, the whole objective of the test being done in the YouTube is to find the Specific Gravity (Density) of the Gold ring. Now, as I look at my Periodic Table at home, at the top of the Density column it is titled (g/cm -3), which means weight (grams being a unit of weight) divided by volume (cubic centimeters).

First, the ring was weighed dry before submerging in water and it's weight of 3.5grams recorded. Second, the bowl of water was set on the scale and it's weight zeroed out using the Tare button. Third, the ring tied on a string is submerged into the water, again not touching the bottom or sides of the bowl, and another weight reading of 0.3grams is recorded. Fourth, the weight of the ring dry 3.5g is divided by the weight of the ring submerged in water 0.3g and the quotient of 11.666 is the Density.

What baffles me is how the digital scale can give a dry weight reading for the gold ring of 3.5g and then a much lower weight of only 0.3g for the same gold ring when suspended in water. How does that work ? Please try to explain in easy-to-understand language if possible. I'm not that good at abstract thinking.

Thanks for your help !

ToddB64

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Last edited by ToddB64; 04-06-2017 at 11:35 PM.
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  #22  
Old 04-04-2017, 09:20 PM
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Ice Scratcher Ice Scratcher is offline
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What was holding the string?

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  #23  
Old 04-04-2017, 11:03 PM
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ToddB64 ToddB64 is offline
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Default Testing Jewelry Value Before Selling.

Originally Posted by Ice Scratcher View post
What was holding the string?

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Ice Scratcher,

I guess you didn't click-on the hyperlinked address for the YouTube video.
(That's the link to the left and right below MY POST FOLLOWS.)

Anyhow, the video host "Chad" had the upper end of the string rolled around a dowel rod, or maybe it was a fishing rod....dunno. You can see it in the video and the rod was obviously supported at each end in some way so that it was horizontal above the water bowl and the rod could be rotated by his fingers to raise and lower the 10K gold ring in or out of the bowl of distilled water.

ToddB64

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