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<p>[QUOTE="Roerbakmix, post: 4141593, member: 100731"]So, last week I bought this silver medieval penny, which was identified by the seller as "an English penny with a king". It was [USER=87271]@AnYangMan[/USER] who identified this coin as a silver penny of</p><p>Diederik van der Ahr, Bishop of Utrecht (the Netherlands) in 1197–1212. </p><p><br /></p><p>The coin had some issues, but the price was right (€32, including postage), and as I was looking for medieval coinage of the Netherlands (which is where I live), I decided to buy it regardless. Also, as some of you may know, I enjoy restoring silver coins. </p><p><br /></p><p>So, the coin:</p><p>[ATTACH=full]1071012[/ATTACH]</p><p>This is a difficult combination of a nice patina (silver sulfide; Ag2S), with some copper oxides (the dark green parts) and beneath that, iron oxide. Also, there are some spots with metal-like horn silver. Care should be taken not to remove the patina. </p><p>[ATTACH=full]1071013[/ATTACH]</p><p>Red arrows: horn silver >> dissolves in sodiumthiosulphate</p><p>Green arrows: copper oxides >> dissolves in synthetic citric acid</p><p>Dark-red arrows: iron oxides >>dissolves in synthetic citric acid</p><p>Overall grey appearance: silver sulfide >> does <b>not</b> dissolve in sodium thiosulphate or citric acid. </p><p><br /></p><p>I proceeded as following:</p><p>1) first, the coin was shortly (60 sec) submerged in a hot solution of sodium thiosulphate in distilled water. This dissolved the spots of horn silver</p><p>2) the coin was submerged in a hot solution of distilled water and citric acid</p><p>3) then, with a bamboo skewer, I scraped over the deposits, without applying too much pressure. This step serves to create small cracks in the deposits, which speeds up the chemical process</p><p>4) step 2 and 3 where repeated multiple times. </p><p>5) the silver beneath the deposits was shinier than the rest of the coin. Sodium thiosulphate was used to darken these spots. </p><p><br /></p><p>So, this was the final result after ~60 mins:</p><p>[ATTACH=full]1071016[/ATTACH]</p><p>COUNT OF HOLLAND, Diederik van der Ahr. Denomination: AR penny, minted: Utrecht, the Netherlands; 1197-1212</p><p>Obv: TЄODЄ - RICVS, facing bust of Dirk van Aare in episcopal regalia; crozier to left. </p><p>Rev: cross pattée; in opposite quarters, pellet-in-annulet and trident with annulet ends </p><p>Weight: 0.58g; Ø:14mm. Catalogue: Van der Chijs VI, 2 ,de Mey 159, de Wit Collection 878. Provenance: Ex. private collection; acq.: 02-2020</p><p>An interesting and scarce type. </p><p><br /></p><p>Hope you enjoyed <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie1" alt=":)" unselectable="on" unselectable="on" />[/QUOTE]</p><p><br /></p>
[QUOTE="Roerbakmix, post: 4141593, member: 100731"]So, last week I bought this silver medieval penny, which was identified by the seller as "an English penny with a king". It was [USER=87271]@AnYangMan[/USER] who identified this coin as a silver penny of Diederik van der Ahr, Bishop of Utrecht (the Netherlands) in 1197–1212. The coin had some issues, but the price was right (€32, including postage), and as I was looking for medieval coinage of the Netherlands (which is where I live), I decided to buy it regardless. Also, as some of you may know, I enjoy restoring silver coins. So, the coin: [ATTACH=full]1071012[/ATTACH] This is a difficult combination of a nice patina (silver sulfide; Ag2S), with some copper oxides (the dark green parts) and beneath that, iron oxide. Also, there are some spots with metal-like horn silver. Care should be taken not to remove the patina. [ATTACH=full]1071013[/ATTACH] Red arrows: horn silver >> dissolves in sodiumthiosulphate Green arrows: copper oxides >> dissolves in synthetic citric acid Dark-red arrows: iron oxides >>dissolves in synthetic citric acid Overall grey appearance: silver sulfide >> does [B]not[/B] dissolve in sodium thiosulphate or citric acid. I proceeded as following: 1) first, the coin was shortly (60 sec) submerged in a hot solution of sodium thiosulphate in distilled water. This dissolved the spots of horn silver 2) the coin was submerged in a hot solution of distilled water and citric acid 3) then, with a bamboo skewer, I scraped over the deposits, without applying too much pressure. This step serves to create small cracks in the deposits, which speeds up the chemical process 4) step 2 and 3 where repeated multiple times. 5) the silver beneath the deposits was shinier than the rest of the coin. Sodium thiosulphate was used to darken these spots. So, this was the final result after ~60 mins: [ATTACH=full]1071016[/ATTACH] COUNT OF HOLLAND, Diederik van der Ahr. Denomination: AR penny, minted: Utrecht, the Netherlands; 1197-1212 Obv: TЄODЄ - RICVS, facing bust of Dirk van Aare in episcopal regalia; crozier to left. Rev: cross pattée; in opposite quarters, pellet-in-annulet and trident with annulet ends Weight: 0.58g; Ø:14mm. Catalogue: Van der Chijs VI, 2 ,de Mey 159, de Wit Collection 878. Provenance: Ex. private collection; acq.: 02-2020 An interesting and scarce type. Hope you enjoyed :)[/QUOTE]
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