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<p>[QUOTE=&quot;AnYangMan, post: 5058127, member: 87271&quot;]This thread as turned into a wonderful love-letter to Malachite in all its forms! But why not show some other minerals equally deserving of our attention? A bit of azurite has already made its way into this thread and I must say it is my favourite kind of patina! [USER=78244]@TypeCoin971793[/USER] and [USER=111645]@posnerfan_48[/USER] always tease me with my everlasting quest for blue patinas…</p><p><br /></p><p>Malachite and azurite are both copper carbonate minerals and whichever forms depends on the partial pressure of CO2 in the environment; azurite only forms when extremely high amounts of dissolved Co2 is present, Malachite under more common but still carbonated circumstances. Plus azurite can also morph back into malachite once conditions change and are no longer suitable for azurite formation. That’s why true and almost wholly azurite patinas are so rare and when you do see both malachite and azurite on one coin, an earlier phase of malachite, subsequently followed by a phase of azurite is more common. So, store your blue patinas well! (Not in a glass of water please <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie2" alt=";)" unselectable="on" unselectable="on" />)! My absolute favourite blue-boy:</p><p><br /></p><p><img src="https://i.ebayimg.com/images/g/QekAAOSwW2VfXS7G/s-l1600.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p><img src="https://i.ebayimg.com/images/g/50kAAOSw4slfXS7K/s-l1600.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p>And in the last Steve Album auction, I bought these two:</p><p><br /></p><p><img src="https://www.numisbids.com/sales/hosted/album/038/image02823.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p><img src="https://www.numisbids.com/sales/hosted/album/038/image00970.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p>Plenty of blue, but what gives these their characteristic two-tone, blue-beige/pink patina that I dig (what the Chinese sometimes call ‘Beijing patina’) is a relatively thin film of cerussite impregnated with moderately fine cuprite crystals. Early Chinese coins, especially spades, are quite high in lead content (cerussite is a lead carbonate), generally higher than their contemporary Greek and Roman counterparts, which is why you rarely encounter it thereon. Both of these spades, but especially the second one, also show something else you often see on Chinese spades: cementation copper! Patches of what seem to be perfectly fine bare copper <i>over</i> the layer of corrosion products. This is happens when in a reducing environment all oxygen is incorporated in other corrosion products. Cuprite from one coin can than precipitate on the other in the form of pure Cu (+CO2).</p><p><br /></p><p><img src="https://media.discordapp.net/attachments/716113030244597764/717861259265179769/image01354.png?width=1182&amp;height=677" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p>You can also see both the cerussite/cuprite and the cementation on this recent purchase. The coin was tightly packed with its neighbours, leading to little malachite and azurite formation. This did allow the cuprite-crystals to grow enourmous! You can easily make them out without magnification, especially on the reverse.</p><p><br /></p><p>Or how about a less-easy to find (and spot) lead product? We’ve seen cerussite, but not yet the lead-oxide Minium (the orange-reddish deposits):</p><p><br /></p><p>[ATTACH=full]1202161[/ATTACH]</p><p><br /></p><p>And to close: a fake patina on a fake Mac coin that at first glance, even under magnification, looks quite realistic!</p><p><br /></p><p>[ATTACH=full]1202165[/ATTACH][/QUOTE]</p><p><br /></p>

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