مروري بر شناسايي رزين هاي دي ترپنوييد در ورني آثار هنري به روش طيف‌سنجي مادون قرمز تبديل فوريه

Review on Identification of Diterpenoid Resins in Artworks Varnishes by FTIR

استفاده از رزين هاي دي ترپنوييد حداقل از قرن ششم هجري در ايران و از قرون ميانه در اروپا جهت ساخت ورني گزارش شده و در طول زمان با دستورالعمل‌هاي مختلف بكار رفته اند. شناسايي اين رزين ها در نمونه هاي تاريخي و بررسي دگرگوني هاي رخ داده در فرآيند كهنگي آن‌ها، به روش هاي مختلفي مورد بررسي و ارزيابي قرار گرفته است. از اين ميان طيف‌سنجي مادون قرمز به‌عنوان يكي از روش هايي كه نياز به نمونه كمي داشته و ارزان و در دسترس است، همواره مورد توجه پژوهشگران بوده است. ساختار شيميايي رزين هاي دي ترپنوييد در دو دسته عمومي طبقه‌بندي مي شوند: رزين هاي مركب از ساختارهاي آبيتان و پيماران شامل كلوفان و تربانتين ونيزي، و رزين هاي متشكل از ساختارهاي لبدان و پيماران شامل سندروس و انواع كوپال. ساختارهاي آبيتان تشكيل بسپار نمي دهند، اما لبدان ها فرآيند بسپارش را طي زماني كوتاه طي مي كنند و به همين دليل نيز بيشترين كارآيي را در ورني هاي روغني – رزيني پيدا كرده اند. همين ويژگي ها موجب عملكرد متفاوت دو دسته رزين فوق طي فرآيند پيري و توليد محصولات تخريب شده كه اين امر تا حدود زيادي در شناسايي ساختار اصلي رزين به روش طيف‌سنجي مادون قرمز تبديل فوريه كمك مي كند. در اين مقاله تلاش شده است تا به بررسي شاخصه هاي شناسايي رزين هاي دي ترپنوييد در طيف بيني مادون قرمز تبديل فوريه به روش مروري پرداخته و تلاش شده است تا شاخصه هاي هر رزين بر اساس گزارش هاي مختلف و ساختار رزين بررسي و معرفي شود. ضمن آنكه به دليل استفاده از رزين ها در ورني هاي روغني – رزيني، شاخصه هاي شناسايي روغن بزرك نيز مورد بررسي و مرور قرار گرفته است. نتايج نشان مي دهد كه فرآيند اكسيداسيون رزين ها در ورني هاي حلالي و روغني – رزيني يكسان بوده اما شناسايي آن‌ها در ساختار ورني هاي روغني – رزيني به دليل تأثير اكسيداسيون روغن بر شاخصه هاي شناسايي طي فرآيند پيري دشوار است.

Making varnishes from diterpenoid resins with the several orders had been common in Iran from 12th Century and it has also been reported in Europe from medieval ages. Identification of these resins in old samples and investigation of their degradations through ageing process have performed by various methods. FTIR spectrometry has always been of interest to researchers because it is cheap, available and it requires little sample material. Ditepenoid resins are classified into two classes: mixture of abietane and pimarane structures resins that include colophony and venetian turpentine, and resins that are formed from labdane and pimarane structures which involve sandarac and copal types. Abietane structures do not polymerized in the time but labdanes and pimaranes polymeriz at a very short time. For this reason, they mostly are used in oil-resin varnishes. These characteristics have led the two classes of resins to operate differently during ageing process and production of degradation products. This differentiation helps to identify to characterize the original structure of resin in the varnish compound in FTIR spectrometry. This article reviews the identification characteristics of diterpenoid resins in FTIR spectrometry and it tries to investigate and introduce every resin characteristics according to their structure from several references. Moreover, identification characteristics of linseed oil is introduced because of its application in oil-resin varnishes. Also, degradation process and its production are also reviewed. Differentiation in chemical structures of diterpenoid resins causes the differentiation of ageing process such the polymerisation of labdanes and pimaranes and cross linking in ageing process produce some new functional groups. Also some functional groups are destroyed during ageing. The changes observed in FTIR spectrometry are inclined oxidation and polymerization of varnishes that in turn changes bands intensity related to OH region, especially in 3000 and 3450 cm-1 and carbonyl region bands. Degradation process of resins in solvent and oil-resin varnishes is same but identification of resin characteristics in oil-resin varnishes is difficult because of effects of oil oxidation on varnish spectra after aging process. Also cross links in varnish structure during aging process cause the formation of some new bands in aged varnishes spectra. Degradation products in resinits and ambers are to some extent like that of old resins and varnishes because their aging process is same.