"خمیر لاجورد" یا "آبی مصری"؟ بررسی ساختاری و هویت‌بخشی مجموعه‌ای از اشیاء منسوب به خمیر لاجورد در موزه ملی ایران

In some of the archeological museum, the variety of blue object are nominated as Egyptian Blue, Lapis lazuli and Lapis lazuli paste. In this research, it was found that there are many mistake in this classification. Lapis lazuli, a brilliant azure-blue color gemstone, is a mixture of minerals, primarily containing the lazurite (blue) with small amounts of calcite, sodalite, and gold-color flecks of pyrite. It has been prized as an ornamental stone for over 6000 years. The most valuable lapis lazuli is the uniform dark blue stone from Badakhshan of Afganistan. This semiprecious blue stone was, and still is, used for jewelry, mosaics and small carvings. Lapis lazuli was also ground and purified to make natural ultramarine blue pigments. The Egyptian blue is the earliest known multicomponent synthetic pigment produced in ancient times in Egypt since the Fourth Dynasty of the Old Kingdom in the 3rd millennium BC, where it has been found as a pigment and formed into small objects such as amulets or beads. Egyptian blue frit is a multicomponent material that was produced by firing a mixture of quartz, lime, a copper compound and an alkali flux to a temperature in the range 850-1000 ◦C. Its principal components are calcium-copper tetrasilicate crystals (cuprorivaite), which produce the blue color, and partially reacted quartz particles bonded together by varying amounts of glass phase. In Mesopotamia from about 1200 to 900 BC, the best information on artefacts of Egyptian blue comes from the destruction debris of Hasanlu in north-west of Iran. Also, the range of Egyptian blue production in the Achaemenid period is the best represented in the excavations at Persepolis. It must be emphasized that "Lapis lazuli Paste" is a wrong term which is not truly exist. In this research, considering the wrong terms which is used for nomination of the collection of blue objects; in the labels, registration records, catalogs and etc, some scientific research was done to specify their characterization. 10 objects from different archaeological sites including Hasanlu, Ziwiyh and Persepolis from the period of 1st millennium BC to Achamenid were selected for this research. These objects were in different size and dimensions, including high jug with a variety of blue color from dark to pale blue, censer, plaque, small head of a young prince or princess and etc. At first, all of the samples were documented and then, structural investigation was realized by binocular microscope, to know condition and texture of their surfaces. Scientific and analytical research was done by SEM-EDX and XRD. As a result, all of these objects was identified as Egyptian blue. Finally, it was required to consider and overview the classification of the group of blue objects, which was wrongly nominated as "lapis lazuli paste", in fact, it does not exist.