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What I need is a substance which could have been mixed by an alchemist and is as gold-like as possible. How about gold itself? Bear with me, here: While there are a lot of things that look ki...
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<blockquote><p>What I need is a substance which could have been mixed by an alchemist and is as gold-like as possible.</p></blockquote><p><strong>How about gold itself?</strong> Bear with me, here:</p><p>While there are a lot of things that look <em>kinda</em> like gold, nothing quite looks as good as the real thing (as pointed out in Cort Ammon's most excellent answer). So, why not use the real thing and have your alchemist accidentally stumble across <a href="https://en.wikipedia.org/wiki/Gold_plating">gold plating</a>, which of course is simply the process whereby relatively very small amounts of gold are deposited onto the surface of an object made of a different substance, ideally with a similar density.</p><p>How could he do this with typical medieval kit (i.e., without readily available electricity)? According to <a href="http://link.springer.com/article/10.1007%2FBF03354479">this paper</a> in JOM, researchers were able to replicate the results of pre-Columbian smiths in Northern Peru using an electrochemical reaction by dissolving gold into an aqueous solution of NaCl + KNO3 + KAl(SO4)2 · 12H2O, achieving gold plating onto copper. The chemicals would have been readily available minerals to a medieval (al)chemist, consisting of ordinary salt, <a href="https://en.wikipedia.org/wiki/Potassium_nitrate">saltpeter</a>, and <a href="https://en.wikipedia.org/wiki/Potassium_alum">potassium alum</a>. In fact, they are all naturally-occurring.</p><p>Alchemists I've seen in fiction tend to use hilariously complex apparatus, have spent many years <a href="https://en.wikipedia.org/wiki/Mercury_poisoning">sniffing mercury vapours</a>, and have weathered many, many failed attempts in search of that elusive ? ⟶ Au formula. It wouldn't be hard to imagine an alchemist cracking open a dusty tome that suggests they need small amounts of the target element as a catalyst to start the reaction. Trembling in anticipation, they add in a pinch of gold dust into the above solution, and soon their entire hunk of metal appears to be pure gold!</p><p>Of course the gold plating would be discovered it as soon as anyone scratched it hard enough, but I think that's the intent, right? Something that is initially very convincing, but doesn't survive scrutiny.</p><p>You specified "it's not gold", and while this would have a very small amount of gold in it, it's still 99.9% "not gold", which I hope satisfies the spirit of your criteria.</p>
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- <p>What I need is a substance which could have been mixed by an alchemist and is as gold-like as possible.</p>
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- <p><strong>How about gold itself?</strong> Bear with me, here:</p>
- <p>While there are a lot of things that look <em>kinda</em> like gold, nothing quite looks as good as the real thing (as pointed out in Cort Ammon's most excellent answer). So, why not use the real thing and have your alchemist accidentally stumble across <a href="https://en.wikipedia.org/wiki/Gold_plating">gold plating</a>, which of course is simply the process whereby relatively very small amounts of gold are deposited onto the surface of an object made of a different substance, ideally with a similar density.</p>
- <p>How could he do this with typical medieval kit (i.e., without readily available electricity)? According to <a href="http://link.springer.com/article/10.1007%2FBF03354479">this paper</a> in JOM, researchers were able to replicate the results of pre-Columbian smiths in Northern Peru using an electrochemical reaction by dissolving gold into an aqueous solution of $\text{NaCl} + \text{KNO}_3 + \text{KAl}(\text{SO}_4)_2 · 12\text{H}_2\text{O}$, achieving gold plating onto copper. The chemicals would have been readily available minerals to a medieval (al)chemist, consisting of ordinary salt, <a href="https://en.wikipedia.org/wiki/Potassium_nitrate">saltpeter</a>, and <a href="https://en.wikipedia.org/wiki/Potassium_alum">potassium alum</a>. In fact, they are all naturally-occurring.</p>
- <p>Alchemists I've seen in fiction tend to use hilariously complex apparatus, have spent many years <a href="https://en.wikipedia.org/wiki/Mercury_poisoning">sniffing mercury vapours</a>, and have weathered many, many failed attempts in search of that elusive $? \to$ Au formula. It wouldn't be hard to imagine an alchemist cracking open a dusty tome that suggests they need small amounts of the target element as a catalyst to start the reaction. Trembling in anticipation, they add in a pinch of gold dust into the above solution, and soon their entire hunk of metal appears to be pure gold!</p>
- <p>Of course the gold plating would be discovered it as soon as anyone scratched it hard enough, but I think that's the intent, right? Something that is initially very convincing, but doesn't survive scrutiny.</p>
- <p>You specified "it's not gold", and while this would have a very small amount of gold in it, it's still 99.9% "not gold", which I hope satisfies the spirit of your criteria.</p>