Technology Recognition of Leather Artifacts Belonging to the Achaemenian period, Artifact from the Salt Mine in Zanjan Chehrabad

Organic materials, due to their vulnerable structure, are considered as rare archeological materials. Therefore, the number of research and literature about these materials is limited. In this project, four leather artifacts found in Chehrabad Salt Mine of Zanjan belonging to Achaemenid period have been studied in three sections: first, identifying the type of animal whose skin has been used in producing these artifacts; second, identifying the tanning materials; and third, identifying the materials used in fat liquor processing. For identifying the animal species, cross section of leather samples were studied using optical microscopy method. Results showed that sample no. 1 is of cow skin, sample no. 2 of goat, and sample no. 3 and 4 are of sheep skin. These results can prove the hypotheses related to animal species. For identifying tanning material, presence of plant tanning agents was studied using ferric chemical test. The results revealed the absence of any tanning agents and this disproves the hypothess related to tanning material. For studying the existence of mineral tanning material, SEMEDS elemental analysis technique was used and the results showed the absence of those mineral material; concluding that no tanning material used in the samples. For identifying the materials used in lubricating process, GC-MS technique was used. Separating organic compounds in samples, this technique also proved the absence of vegetable tanning materials in the process of manufacturing these artifacts and this confirmed the results of ferric chemical test. Comparing the compounds identified by GC with MS library, some fatty acids were recognized. Linoleic acid and stearic acid were identified in sample 1 which shows the presence of sunflower oil. Oleic acid and capric acid (decanoic acid) were identified in sample 2, but no material could be found with these two fatty acids. Probably two materials have been used in lubricating process of this sample. In sample no. 3, only oleic acid was found. For sample 4, no fatty acid ould be found, proving the absence of oil and fat in this artifact. Finally for ensuring the results of GC-MS, FT-IR technique was used. In this regard, two important absorbance bands of fatty acids i.e. O-H and C=O bonds were considered. All samples, except sample no. 4, showed absorption in mentioned areas. Thus FT-IR confirmed the result of GCMS analysis. These results support the hypotheses given about the materials used in lubricating process of the samples.