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<p>[QUOTE=&quot;robinjojo, post: 24494811, member: 110226&quot;]The metal that was used in Rome in imperial times was orichalcum, what we call brass, which is composed of a combination of copper and zinc.&nbsp; Bronze, on the other hand, is an alloy of copper and tin. </p><p><br /></p><p>Now I am not sure what proportions of copper and tin was used, but the yellow color is very distinct from the red of bronze.&nbsp; I think this is a factor on how quickly an orichalcum coin tones, versus one that is bronze.&nbsp; I think this is also a factor on how long a coin, once cleaned tones again.&nbsp; There are agents, notably liver of sulfur, that can accelerate the process, but even the use of this chemical has limits. </p><p><br /></p><p>I have brass objects that have not really changed much in color over the years.&nbsp; On the other hand I have bronze coins that change (darken) rather quickly.&nbsp; I attribute this difference to the amount of copper in the alloy.&nbsp; My Byzantine bronze coins must have a high copper content, since they tend to tone more quickly compared to Roman imperial orichalcum coins. </p><p><br /></p><p>This is coin that I bought recently.&nbsp; It was excessively cleaned in my view, with bright shiny surfaces in areas, along with heavy deposits over much of the coin, especially on the obverse.&nbsp; Unfortunately I don&#039;t have &quot;before&quot; photos; I was quite intent on attending to the coin.</p><p><br /></p><p>Some areas were heavily encrusted with heavy black deposits.&nbsp; There are also those rock hard green deposits.&nbsp; My objective was to mitigate the deposits, but not eliminate them entirely.&nbsp; I also needed to adjust the color so that it is darker and more in agreement with the deposits. </p><p><br /></p><p>Using chemicals on coins is a fraught undertaking and I don&#039;t recommend using them without knowing their effects. One can never be absolutely certain about the condition of the underlying metal, which could be corroded.&nbsp; There is an element of luck and in this case the surfaces are intact.</p><p><br /></p><p>The deposits were treated first with the coin immersed in distilled water to loosen up any soft deposits.&nbsp; This yielded very minimal results.&nbsp; The next step was to apply naval jelly only on the areas of heavy deposits, not the entire coin.&nbsp; This was done with cotton swabs and wooden toothpicks.&nbsp; Many applications were done in succession, taking care not to allow the acid to stay on the surface for more than roughly 30 seconds, followed by rinsing with distilled water, drying, and examination.&nbsp; Once the deposits were at &quot;acceptable&quot; levels (totally subjective), the coin was treated with diluted (with very hot distilled water) liver of sulfur. I forgot the ratio, but it was around 5-6 drops to roughly two tablespoons of distilled water.&nbsp; Again, cotton swabs were used on applying, followed by distilled water rinses.&nbsp; The coin did darken, not as much as it would if it were bronze, but the cleaned surfaces are quite apparent, nothing can be done about that. </p><p><br /></p><p>Note that the deposits are still there, along with some green spots.&nbsp; Generally I don&#039;t like treating ancient coins this way.&nbsp; I&#039;m from the school of live and let live, but sometimes a coin can be helped with measured and knowledgeable treatment.&nbsp;&nbsp; </p><p><br /></p><p><b>Vespasian, AE dupondius, Rome, 74 AD, COS VI.</b></p><p><b>RIC 567 </b></p><p><b>12.63 grams</b></p><p><b><br /></b></p><p><b>[ATTACH=full]1552369[/ATTACH] </b>[/QUOTE]</p><p><br /></p>

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