Evaluation of the degradation and stability of soot ink made based on ancient texts under aging conditions. Soot ink is one of the inks that has been widely used in written works. Some of which are currently in our custody, so it is necessary to examine their degradation in order to prevent their further degradation. In this regard, in the present study, the degradation rate and stability of soot ink were investigated. The question of this study is what level of degradation and stability do the manufactured inks have? The purpose of this study was to examine soot ink, which was used in paper works, using laboratory instruments, pH meter, FTIR, optical microscope, colorimeter, and tensile strength meter.
To prepare the samples, the immersion method was used to impregnate the paper with ink, and an incubator was used to age the samples. The results of the acidity test (pH measurement) of the ink-impregnated papers show that the accelerated moisture-thermal aging process, especially after a period of 12 days, causes a decrease in pH compared to the samples before aging. The results of microscopic observations show that the aged sample has suffered from breakage in addition to the ink of the paper fibers. Analysis of the ATR-FTIR spectra in the carbon black sample indicates that cellulose undergoes structural changes during aging, but most of the changes are in the structure of the ink. According to the studies conducted, the results of this research indicate that the carbon black ink has relatively good stability during aging.

Historic bridges represent complex structural systems that have endured centuries of environmental exposure, functional transformation, and human intervention. Due to their structural configuration and location within dynamic riverine contexts, they are particularly vulnerable to natural forces, material decay, and incompatible repairs. Conservation doctrine has consistently emphasized that intervention must be grounded in knowledge. Documents such as the Venice Charter, the Burra Charter, the Nara Document on Authenticity, and the ICOMOS Principles for the Analysis and Restoration of Architectural Heritage stress that understanding a monument’s historical development, material composition, and structural performance is essential before any action is taken. Building on this understanding, the present study develops and applies an integrated damage diagnosis approach to the historic Bridge-Dam of Izadkhast. Although Iranian historic bridges have been widely studied, previous research has often addressed historical interpretation, qualitative assessment, and structural modeling separately. In many instances, laboratory testing and structural calculations were treated as isolated technical exercises rather than as components of conservation decision making. This separation has occasionally led to reinforcement strategies that exceed actual structural needs and conflict with principles such as minimal intervention and respect for authenticity. The principal research gap therefore lies in the absence of a coherent methodological framework that integrates historical studies, qualitative damage assessment, laboratory material testing, and quantitative structural behavior analysis into a unified and conservation oriented decision making model. The Izadkhast Bridge-Dam was selected as the case study because of its historical and structural importance. Located along the Historic route from Isfahan to Shiraz via Izadkhast, it once played a strategic role in regional communication and maintained a functional relationship with the nearby caravanserai. Built across a seasonal river prone to flooding, the structure was originally designed to serve caravan traffic. In later periods, however, the passage of automobiles and heavier transport introduced load conditions that had not been anticipated in the original architectural conception. As a result, the bridge was subjected to stresses exceeding its intended structural capacity. Despite these pressures, it remained functional for centuries. Only in recent decades have climatic variability, renewed water flow after extended drought, inappropriate restoration efforts, and insufficient river management significantly increased its vulnerability. The methodology adopted in this research consisted of six interconnected stages: (1) historical analysis and investigation of the structural evolution of the monument; (2) direct observation and qualitative assessment of the current condition; (3) qualitative and semi-quantitative analysis of mortars and qualitative assessment of materials; (4) structural analysis and evaluation of the overall structural behavior; (5) safety assessment through quantitative analyses and structural testing; and (6) final judgment and data integration. In this method, Laboratory investigations were conducted to determine the physical and chemical properties of mortars and bricks, and structural behavior under gravity, seismic forces, wind, and hydraulic actions was analyzed through finite element modeling using ANSYS software. The findings demonstrate that a comprehensive understanding of the monument requires the simultaneous interpretation of historical documentation, field evidence, material characteristics, and structural modeling results. Historical analysis revealed that major damage resulted from changes in function, excessive loading beyond traditional use patterns, destructive floods particularly the flood of 1956 CE. and alterations in river morphology caused by human intervention. Qualitative assessment identified inconsistencies in restoration management, incomplete conservation measures, deterioration of mortars, and neglect of riverbed maintenance as significant contributors to the bridge’s current condition. Material analyses indicated that lime mortars (cold sarooj) were intentionally employed in water exposed sections, while gypsum–lime mortars were used in arches and passageways, reflecting functional adaptation to environmental conditions. Although bricks quality was relatively low due to manufacturing and firing limitations, this characteristic forms part of the bridge’s original material system and does not in itself indicate structural weakness. Structural analyses showed that the bridge performs satisfactorily under gravitational and seismic loads. The vulnerable structural points was identified in relation to hydrodynamic flood forces and at the junction between the end piers and the natural riverbanks.
The integratetion of the obtained results indicate that most observed damages do not stem from inherent structural vulnerability, but rather from the disruption of the bridge’s historical equilibrium. Changes in functional loads, incompatible restoration materials, interruption of structural continuity, and hydromorphological alterations in the riverbed have collectively intensified deterioration. Numerical modeling confirmed that heavy structural reinforcement or radical alteration of the structural system is unnecessary. Instead, conservation efforts should focus on correcting inappropriate past restorations, locally reinforcing critical points, stabilizing and organizing the riverbed and establishing a continuous maintenance system. This study demonstrates that that quantitative structural analysis can meaningfully inform conservation decisions only when interpreted in direct connection with historical understanding and material characterization. Detached numerical assessments risk misdiagnosis and unnecessary intervention. Accordingly, the research advocates a shift from reactive, episodic restoration toward preventive and integrated management of historic bridges. Ultimately, this research proposes a transferable analytical framework for the conservation of historic bridges in Iran and comparable contexts. By integrating historical research, qualitative damage assessment, laboratory based material evaluation, structural stability assessment, and finite element analysis into a unified diagnostic process, the study provides a methodological model that supports minimal, authenticity compatible, and scientifically grounded conservation strategies, while preventing costly and irreversible interventions.