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<p>[QUOTE=&quot;Howard Black, post: 3562155, member: 97119&quot;]One last muse on toning:</p><p><br /></p><p>The exact same phenomenon that causes the iridescent colors on a coin was used by <a href="https://en.wikipedia.org/wiki/Gabriel_Lippmann#Colour_photography" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Gabriel_Lippmann#Colour_photography" rel="nofollow">Gabriel Lippmann</a> in 1886 to create a full-color image on a <i>monochrome</i> plate -- he was a physicist who understood light interference effects, and did the impossible -- and it earned him a Nobel Prize.</p><p><br /></p><p>Here (below) is a sample of what he created. Remember, <b><i>all</i></b> of those colors are produced by the same principle involved in rainbow toning of coins. They&#039;re not inks, pigments, or dyes. Just the interaction between the wavelengths of the different colors and a layer of reflective mercury behind the emulsion.</p><p><br /></p><p>If you read the article linked to his name, you&#039;ll see that he was a polymath, with significant inventions in many fields.</p><p><br /></p><p>I would not be surprised if he was a numismatist too. For that matter, I would not be surprised if it was the toning he&#039;d observed on coins that provided the spark of inspiration that culminated in that Nobel Prize.</p><p><br /></p><p><img src="https://upload.wikimedia.org/wikipedia/commons/8/87/Lippmann_photo_flowers.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" />[/QUOTE]</p><p><br /></p>

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