سنجش عيار نقره سكه‌هاي درهم عباسي قرن دوم هجري، متعلق به موزۀ ملي ايران، با استفاده از آزمايش XRF

Silver Finesse of Coinage of 2nd AH, from the collection of National Museum of Iran, Using XRF Method

پژوهش سكه‌ها اطلاعاتي بي‌واسطه و دست اول از فهم گذشته است. فناوري و بستر ميان رشته‌اي مي‌تواند ارزش مضاعفي ايجاد كند كه شايد بدون آن دستيابي به آنها ممكن نباشد. داده‌هاي بدست آمده از آناليز غيرمخرب اطلاعاتي توليد مي كند كه الزاما در متون تاريخي وجود ندارد؛ يا در سكه‌شناسي چون معمولا بستر پيدايي آنها نامشخص است نسبت به مواد فرهنگي بر جا دچار نقصان هستند و نمي‌توان در اين زمينه نظري ارائه داد. براي سنجش خلوص نقرۀ تعدادي از سكه‌هاي قرن دوم هجري خلافت عباسي كه از گنجينۀ موزۀ ملي ايران هستند، از دستگاه XRF قابل حمل استفاده شد. نتايج حاصله كه به روش كمّي- كيفي به دست آمد مورد مطالعۀ آماري قرار گرفت. از بين نتايج حاصل، به غير از نقره كه در سكه‌هاي درهم محور و فرض اصلي مقاله است، به دو فلز مس و سرب در سكه‌ها نيز توجه شد زيرا ضمن ارتباطي تنگاتنگ با نقره، در مسائل مختلفي از جمله عيار نقره و مسائل فني تعيين كننده هستند. ضمن ترسيم جداول و نمودارها، عيار نقره بر اساس درصد وزني به دست آمد كه تفسير آنها گوياي عيار بيشتر سكه‌هاي مركز خلافت، مدينه‌السلام، و تمايزشان از سكه‌هاي ضرابخانه‌هاي ديگر است. ضمن اين كه برخي ناخالصي‌هاي شاخص، مس و سرب، در سكه‌هاي مدينه‌السلام كمتر از گروه سكه‌هاي ديگر است. مي‌توان ناخالصي‌هاي مربوط به مس را موثر در عيار دانست به اين نحو كه احتمالا آگاهانه به تركيب فلزي اضافه مي‌شد و ناخالصي‌هاي مربوط به سرب را به دليل عدم تأثيرگذاري در عيار، اهمال‌كاري فني تلقي كرد.

Introduction Investigating coins reveals firsthand and immediate information to understand “past”. Enjoying technology and providing an interdisciplinary context can extract physical and chemical data, which potentially gain double relevant value inaccessible in the absence of the technology. The data that achieved by such nondestructive analyzing methods result most valuable information which necessarily is absent in historical written sources or numismatics naturally lacks it, because of unknown archaeological provenance, comparing to in situ material culture. XRF portable device used to measure silver finesse of some Abbasid coins of 2nd AH century. The authors statistically studied the results that achieved quantitative-qualitatively. The consequent finesse, as weight percentage, indicates that finesse of capital city of Madinat al-Salam is distinguished and higher than silver finesse of coins from the other mints. Furthermore, the former has lower characteristic metal impurities, copper and lead, comparing to the coins of mints other than capital city. One can suggest copper impurity as intentional addition to manipulate alloy finesse, whereas lead impurity as technical negligence and with no effect on finesse. Materials and Methods Some 41 coins of Madinat al-Salam and other mints picked up of the collection of National Museum of Iran, while 24 minted in Madinat al-Salam, the capital, and the other 17 ones coined in the other mints. A portable XRF instrument used to analyze the coins. The experiment focused on silver, as the base of dirhams, copper and lead. The results placed on charts and statistically analyzed. Results Despite of physical similarities of the coins, rate of copper in the coins of the capital, Madinat al-Salam, is lower than the coins of other mints, while the rate of lead follows the same equality, where it is higher in the out of capital coins. The copper rate has inverse ratio to the silver finesse, whereas the former decreases when the latter increases, and vice versa. However, statistical analysis indicates no relevance between fluctuation of lead and silver finesse, while getting away from capital, Madinat al-Salam causes higher rate of lead. Conclusions The authors suggest an intention in higher purification of the Madinat al-Salam dirhams, in which the authorities attempted to manipulate the rate of copper and present finer dirhams for the capital, however, we do not know why. One can suggest the fluctuation of lead as a technological relevance, which means further distance from the capital leads to more rate of lead that probably rooted in weakness of facilities at outer mints as a relevance to Political sovereignty. It means harder purification of silver, however, there is no meaningful connection between rates of lead and copper. Funding Present paper used postdoctoral Allameh Tabatabaei fund of Iranian National Elite Foundation, which hosted by Dr. Gholamreza Avani. Authors’ Contribution The authors declare no conflict of interests.