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<p>[QUOTE="AussieCollector, post: 3096096, member: 81093"]Hi all</p><p><br /></p><p>I just wanted to share some learning/experience of specific gravity tests for my coins.</p><p><br /></p><p>This is not intended to be a best practice overview of conducting specific gravity tests. Rather, I am just sharing my journey to date, in the hope that it may be of interest and/or benefit to fellow collectors.</p><p><br /></p><p><b>Context to my coins</b></p><p><br /></p><p>My coin collection (or amassed coins to be more accurate) is somewhat eclectic. I am attempting to build a coin collection that more or less spans from the dawn of coins, to pre-modern/decimal. My passion is most definitely in the age of sail/discovery, closely followed by Byzantium and ancient coins.</p><p><br /></p><p>With that in mind, the structure of my collection is as follows:</p><p><br /></p><p>Ancient – 500BC to 500AD (pretty much Roman and Greek coins)</p><p><br /></p><p>Medieval – 500AD to 1500AD (which solely consists of Byzantium coins at this stage, as other medieval coins are both small and expensive)</p><p><br /></p><p>Age of sail and discovery – 1500 to 1862 (weird that I have such a precise end date - I know - but that’s the generally accepted date of when the age of sail concluded)</p><p><br /></p><p>European settlement of Australia – 1788 to 1910 (finishing in 1910, which was when we started to mint our own coins)</p><p><br /></p><p>Australian pre-decimal coins – 1911 to 1966 (finishing with the conversion to the dollar)</p><p><br /></p><p>I’m going to focus on the first 3 categories, as they’re the most interesting (in my view) and the coins are more difficult to authenticate.</p><p><br /></p><p><b>Equipment</b></p><p><br /></p><p>Pocket scales (to two decimal places)</p><p><br /></p><p>Cup of water</p><p><br /></p><p>Thin floss</p><p><br /></p><p>Jerry-rigged wire to suspend coins (towards the end – see troubleshooting)</p><p><br /></p><p><b>Method</b></p><p><br /></p><p>Simple water suspension method, with weight of coin (dry weight) divided by coin suspended in water (suspended).</p><p><br /></p><p><b>Results</b></p><p><br /></p><p>Alrighty, now for my trial and error.</p><p><br /></p><p><u>8 Reales, Potosi, 1666</u></p><p>Dry weight - 27.06g</p><p>Suspended 2.64g</p><p>SG - 10.25</p><p><br /></p><p>So far so good, SG is very close to what you’d expect. Perhaps a bit under.</p><p><br /></p><p><u>8 Reales Mexico 1821</u></p><p>Dry weight - 27.01</p><p>Suspended - 2.63</p><p>SG - 10.27</p><p><br /></p><p>Seems ok, even better than the cob in terms of expected SG.</p><p><br /></p><p><u>Leeuwendaalder 1641</u></p><p>Dry weight - 26.73</p><p>Suspended - 2.67</p><p>SG - 10.01</p><p><br /></p><p>Given the Leeuwendaalders were only 75% silver, this is about what you’d expect – perhaps a smidgen under, but even then – that’s assuming the remainder of the composition is copper, which it may not be entirely. More on this later.</p><p><br /></p><p>My first real surprise was the Ducat.</p><p><br /></p><p><u>1648 Dutch Ducat</u></p><p>Dry weight - 3.48g</p><p>Suspended - 0.17g</p><p>SG - 20.47</p><p><br /></p><p>See…. here’s the thing…. fun fact, 24 carat gold is 19.4. So this is… more than pure gold?? Now the Ducat is 98.6% gold (unlike many other gold coins of the period, which were closer to 90%) – so you’d expect a high SG. But not THIS high.</p><p><br /></p><p>Another fun fact, if the suspended weight was 0.18, the SG would be 19.3 – which is almost exactly as you’d expect.</p><p><br /></p><p>0.01 – it’s important. More on this under troubleshooting.</p><p><br /></p><p>My second surprise was the Hekte.</p><p><br /></p><p><u>El Hekte – Lesbos, 377 to 326 BC</u></p><p>Dry weight - 2.56g</p><p>Suspended - 0.21g</p><p>SG - 12.19</p><p><br /></p><p>Again, there’s a problem here. My understanding was that Hektes, being electrum, were a 50-50 (ish) gold silver mix, which should put the SG at about 14 to 15. I stressed over this result for almost a week, trying to find information on what the reading should be</p><p><br /></p><p>More on this under troubleshooting.</p><p><br /></p><p><u>Denarius – Marcus Aurelius 140 to 144 AD</u></p><p>Dry weight – 3.52</p><p>Suspended weight – 0.36</p><p>SG – 9.78</p><p><br /></p><p>Not terrible, but not exactly what you’d expect either. More on this one under troubleshooting too.</p><p><br /></p><p><u>Hyperpyron – Andronicus II & III</u></p><p>Dry weight – 3.89</p><p>Suspended weight – 0.31</p><p>SG – 12.55</p><p><br /></p><p>Like the Hekte, this was significantly under what I was expecting – particularly because this was a more modern coin, supposedly consisting of 11 or 12 carats, with the rest being silver and copper (which by my calculations should have come in at 14 or something).</p><p><br /></p><p>More on this below.</p><p><br /></p><p><b>Troubleshooting</b></p><p><br /></p><p><u>Dip and let it settle</u></p><p><br /></p><p>So often the scales will fluctuate for a bit when using floss in particular, and you just need to wait a few of seconds to let it all settle down to get an accurate reading. Sometimes the non-settled weight of a suspended coin can be +/- 0.02 – which is significant on smaller coins.</p><p><br /></p><p>The differences on the SG reading can be massive.</p><p><br /></p><p><u>Ancient coins and SGs</u></p><p><br /></p><p>Before I get into the floss vs wire, the context of ancient coins and SGs is important.</p><p><br /></p><p>As it turns out, it’s not as simple as “this coin is 50% gold, 25% silver, and 25% copper and therefore should be X specific gravity”.</p><p><br /></p><p>Specific gravity as a test is great for single or binary alloys. But not so much for 3 or more, and especially not so much for ancient coins, where there are also unknown metals and materials present.</p><p><br /></p><p>I found some research on Hekte coins here:</p><p><a href="https://www.scribd.com/document/81156859/Electrum-coins-and-their-specific-gravity-Barclay-V-Head" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.scribd.com/document/81156859/Electrum-coins-and-their-specific-gravity-Barclay-V-Head" rel="nofollow">https://www.scribd.com/document/81156859/Electrum-coins-and-their-specific-gravity-Barclay-V-Head</a></p><p>(I found the table at the end to be particularly useful)</p><p><br /></p><p>And electrum and other gold alloy coins here:</p><p><a href="https://pdfs.semanticscholar.org/f3a9/a9d85d3afb43ea83442445306867bf6afaf7.pdf" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://pdfs.semanticscholar.org/f3a9/a9d85d3afb43ea83442445306867bf6afaf7.pdf" rel="nofollow">https://pdfs.semanticscholar.org/f3a9/a9d85d3afb43ea83442445306867bf6afaf7.pdf</a></p><p>(really good discussion in this article on the impact unknown metals and compositions have on SG)</p><p><br /></p><p><u>Floss vs suspended wire</u></p><p><br /></p><p>FLOSS MAKES A DIFFERENCE – and not in a good way.</p><p><br /></p><p>You’d think it wouldn’t, but it most definitely does. The smaller the coin, the bigger the difference it makes. On the larger crown sized coins, the difference becomes almost a non-issue (almost). But on the small coins, it can mean the difference between an acceptable range, and suspected forgery – either modern or contemporary.</p><p><br /></p><p>Using the wire method is by far superior, because you can tare the weight once you know how much water it displaces. With floss, this isn’t possible, because the floss will just float at the top.</p><p><br /></p><p>I haven’t listed all the coins I tested above, but here are some SGs using suspended (and tared) wire:</p><p><br /></p><p>Ducat – measurements came in at 3.48/0.18 = 19.30. It came in exactly as expected using the tared suspended wire technique.</p><p><br /></p><p>Hekte – measurements came in at 2.56/0.20 = 12.80. A significant and important difference, with the assumed gold content jumping from ~30% to ~40%.</p><p><br /></p><p>Denarius – measurements came in at 3.52/0.35 = 10.01. Again, the Denarius shot up from what was a bit low, to exactly where it should have been.</p><p><br /></p><p>Leeuwendaalder – measurements came in at 26.73/2.66 = 10.05. Not a huge difference (as the coin is larger, and therefore the impact of the floss on the SG is smaller), but I still saw a difference and a shift up. And it’s achingly close to exactly what a 75% silver 25% copper mix should be – 10.08.</p><p><br /></p><p>Hpyerpyron – measurements cam in at 3.89/0.29 = 13.41. This is a really significant difference, with the assumed gold content of the coin jumping significantly.</p><p><br /></p><p><b>Learnings</b></p><p><br /></p><p><u>Your method of suspension is important</u></p><p><br /></p><p>Overall, switching from floss suspension to wire suspension results in a shift in exactly the right way on my coins. Coins that were too high, came down, and coins that were too low, went up. It's just more accurate.</p><p><br /></p><p><u>The science of SG for ancient coins</u></p><p><br /></p><p>Due to the nature of SG testing on ancient coins, I have spend undue hours wondering/stressing about the authenticity coins. I thought it would be a more precise science than it actually is.</p><p><br /></p><p><u>Accuracy</u></p><p><br /></p><p>I also need to get scales with 3 or even 4 decimal places. 2 decimal places are plenty for dry weight, but it isn’t for suspended weight.</p><p><br /></p><p>0.01 can make a big difference when calculating the SG of smaller coins. Again, on the Hekte, a lack of clarity of 0.01 potentially results in an artificial low of 12.19, or an artificial high of of 13.63. The margin of error is unacceptably huge!</p><p><br /></p><p>I have somewhat gotten around this by multiple tests and finding the mode, but it’s not ideal.</p><p><br /></p><p><u>Question</u></p><p><br /></p><p>Finally - Question, question, question. Test. Fail. Have another go. Get it wrong. Try again.</p><p><br /></p><p>Hope that was of interest to some, and let me know if you have any comments, musings, corrections, or recommendations.</p><p><br /></p><p>Cheers</p><p><br /></p><p>AussieCollector[/QUOTE]</p><p><br /></p>
[QUOTE="AussieCollector, post: 3096096, member: 81093"]Hi all I just wanted to share some learning/experience of specific gravity tests for my coins. This is not intended to be a best practice overview of conducting specific gravity tests. Rather, I am just sharing my journey to date, in the hope that it may be of interest and/or benefit to fellow collectors. [B]Context to my coins[/B] My coin collection (or amassed coins to be more accurate) is somewhat eclectic. I am attempting to build a coin collection that more or less spans from the dawn of coins, to pre-modern/decimal. My passion is most definitely in the age of sail/discovery, closely followed by Byzantium and ancient coins. With that in mind, the structure of my collection is as follows: Ancient – 500BC to 500AD (pretty much Roman and Greek coins) Medieval – 500AD to 1500AD (which solely consists of Byzantium coins at this stage, as other medieval coins are both small and expensive) Age of sail and discovery – 1500 to 1862 (weird that I have such a precise end date - I know - but that’s the generally accepted date of when the age of sail concluded) European settlement of Australia – 1788 to 1910 (finishing in 1910, which was when we started to mint our own coins) Australian pre-decimal coins – 1911 to 1966 (finishing with the conversion to the dollar) I’m going to focus on the first 3 categories, as they’re the most interesting (in my view) and the coins are more difficult to authenticate. [B]Equipment[/B] Pocket scales (to two decimal places) Cup of water Thin floss Jerry-rigged wire to suspend coins (towards the end – see troubleshooting) [B]Method[/B] Simple water suspension method, with weight of coin (dry weight) divided by coin suspended in water (suspended). [B]Results[/B] Alrighty, now for my trial and error. [U]8 Reales, Potosi, 1666[/U] Dry weight - 27.06g Suspended 2.64g SG - 10.25 So far so good, SG is very close to what you’d expect. Perhaps a bit under. [U]8 Reales Mexico 1821[/U] Dry weight - 27.01 Suspended - 2.63 SG - 10.27 Seems ok, even better than the cob in terms of expected SG. [U]Leeuwendaalder 1641[/U] Dry weight - 26.73 Suspended - 2.67 SG - 10.01 Given the Leeuwendaalders were only 75% silver, this is about what you’d expect – perhaps a smidgen under, but even then – that’s assuming the remainder of the composition is copper, which it may not be entirely. More on this later. My first real surprise was the Ducat. [U]1648 Dutch Ducat[/U] Dry weight - 3.48g Suspended - 0.17g SG - 20.47 See…. here’s the thing…. fun fact, 24 carat gold is 19.4. So this is… more than pure gold?? Now the Ducat is 98.6% gold (unlike many other gold coins of the period, which were closer to 90%) – so you’d expect a high SG. But not THIS high. Another fun fact, if the suspended weight was 0.18, the SG would be 19.3 – which is almost exactly as you’d expect. 0.01 – it’s important. More on this under troubleshooting. My second surprise was the Hekte. [U]El Hekte – Lesbos, 377 to 326 BC[/U] Dry weight - 2.56g Suspended - 0.21g SG - 12.19 Again, there’s a problem here. My understanding was that Hektes, being electrum, were a 50-50 (ish) gold silver mix, which should put the SG at about 14 to 15. I stressed over this result for almost a week, trying to find information on what the reading should be More on this under troubleshooting. [U]Denarius – Marcus Aurelius 140 to 144 AD[/U] Dry weight – 3.52 Suspended weight – 0.36 SG – 9.78 Not terrible, but not exactly what you’d expect either. More on this one under troubleshooting too. [U]Hyperpyron – Andronicus II & III[/U] Dry weight – 3.89 Suspended weight – 0.31 SG – 12.55 Like the Hekte, this was significantly under what I was expecting – particularly because this was a more modern coin, supposedly consisting of 11 or 12 carats, with the rest being silver and copper (which by my calculations should have come in at 14 or something). More on this below. [B]Troubleshooting[/B] [U]Dip and let it settle[/U] So often the scales will fluctuate for a bit when using floss in particular, and you just need to wait a few of seconds to let it all settle down to get an accurate reading. Sometimes the non-settled weight of a suspended coin can be +/- 0.02 – which is significant on smaller coins. The differences on the SG reading can be massive. [U]Ancient coins and SGs[/U] Before I get into the floss vs wire, the context of ancient coins and SGs is important. As it turns out, it’s not as simple as “this coin is 50% gold, 25% silver, and 25% copper and therefore should be X specific gravity”. Specific gravity as a test is great for single or binary alloys. But not so much for 3 or more, and especially not so much for ancient coins, where there are also unknown metals and materials present. I found some research on Hekte coins here: [url]https://www.scribd.com/document/81156859/Electrum-coins-and-their-specific-gravity-Barclay-V-Head[/url] (I found the table at the end to be particularly useful) And electrum and other gold alloy coins here: [url]https://pdfs.semanticscholar.org/f3a9/a9d85d3afb43ea83442445306867bf6afaf7.pdf[/url] (really good discussion in this article on the impact unknown metals and compositions have on SG) [U]Floss vs suspended wire[/U] FLOSS MAKES A DIFFERENCE – and not in a good way. You’d think it wouldn’t, but it most definitely does. The smaller the coin, the bigger the difference it makes. On the larger crown sized coins, the difference becomes almost a non-issue (almost). But on the small coins, it can mean the difference between an acceptable range, and suspected forgery – either modern or contemporary. Using the wire method is by far superior, because you can tare the weight once you know how much water it displaces. With floss, this isn’t possible, because the floss will just float at the top. I haven’t listed all the coins I tested above, but here are some SGs using suspended (and tared) wire: Ducat – measurements came in at 3.48/0.18 = 19.30. It came in exactly as expected using the tared suspended wire technique. Hekte – measurements came in at 2.56/0.20 = 12.80. A significant and important difference, with the assumed gold content jumping from ~30% to ~40%. Denarius – measurements came in at 3.52/0.35 = 10.01. Again, the Denarius shot up from what was a bit low, to exactly where it should have been. Leeuwendaalder – measurements came in at 26.73/2.66 = 10.05. Not a huge difference (as the coin is larger, and therefore the impact of the floss on the SG is smaller), but I still saw a difference and a shift up. And it’s achingly close to exactly what a 75% silver 25% copper mix should be – 10.08. Hpyerpyron – measurements cam in at 3.89/0.29 = 13.41. This is a really significant difference, with the assumed gold content of the coin jumping significantly. [B]Learnings[/B] [U]Your method of suspension is important[/U] Overall, switching from floss suspension to wire suspension results in a shift in exactly the right way on my coins. Coins that were too high, came down, and coins that were too low, went up. It's just more accurate. [U]The science of SG for ancient coins[/U] Due to the nature of SG testing on ancient coins, I have spend undue hours wondering/stressing about the authenticity coins. I thought it would be a more precise science than it actually is. [U]Accuracy[/U] I also need to get scales with 3 or even 4 decimal places. 2 decimal places are plenty for dry weight, but it isn’t for suspended weight. 0.01 can make a big difference when calculating the SG of smaller coins. Again, on the Hekte, a lack of clarity of 0.01 potentially results in an artificial low of 12.19, or an artificial high of of 13.63. The margin of error is unacceptably huge! I have somewhat gotten around this by multiple tests and finding the mode, but it’s not ideal. [U]Question[/U] Finally - Question, question, question. Test. Fail. Have another go. Get it wrong. Try again. Hope that was of interest to some, and let me know if you have any comments, musings, corrections, or recommendations. Cheers AussieCollector[/QUOTE]
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