نشریه مطالعات در دنیای رنگ
سال دوازدهم شماره 3 (پیاپی 46، پاییز 1401)

In the distant past, painters, scribes, dyers, and other artists have always created different forms of art with pigments. The beginning of pigment usage goes back to early human societies. Pigments are important from an aesthetic point of view, highlighting the differentiation of objects and influencing human thoughts and feelings. Moreover, the identification of traditional pigments is essential for conservation, restoration, historical interpretation of artworks, and understanding the evolution of art. Therefore, this research aims to provide comprehensive knowledge of traditional pigments, in which, in this report, two pigments, including white lead and red lead, have been discussed. Actually, in this research, by collecting the studies of other researchers and examining the current knowledge of this field to evaluate and categorize these pigments from the point of view of their structure, applications, degradation, evolution throughout history, production process furthermore the methods of synthesis, identification in different artworks and identification methods have been discussed. Accordingly, this study paves the way for future studies on historical samples composed of these compounds. 

Nowadays, despite the presence of synthetic dyes, due to the environmental damage caused by these substances, the approach of returning to natural sources has been revived. Meanwhile, the indigo plant is one of the best plant sources to achieve blue color. Much research has been conducted to extract dyes from indigo and woad since long ago. The purpose of this research is to collect the studies done in this field and, secondly, to use the results of previous research by researchers to improve the extraction methods. The results of the research showed that several methods, such as traditional, hot water, microbial, enzyme, microwave, etc., could be applied. It was also found that variables such as oxidation speed, oxidation time, alkaline environment of fermentation, type of alkaline material, resting time of fermentation, etc. influence the extraction process of indigo and woad dyes, the effect of pH is much important.</em>.</em>

The deposits of dispersed dyes on dyed polyester fibres are an important problem in polyester fibre dyeing that should be tackled properly. These dyes deteriorate the wash, rubbing, and sublimation fastness and the brightness of the dyed fibres, especially deep-dyed ones. Therefore, clearing these surface dyes is necessary. Conventionally, a reduction clearing process is used to remove the surface dyes, in which sodium dithionite, a reductant, and sodium hydroxide, an alkaline, are used. This process has a significant part in removing surface oligomers and auxiliaries, such as carriers. Unfortunately, this process is not environment friendly, and the derivatives of its chemicals are toxic to human health, and there are technological and economic issues associated with this process. In recent years, numerous research for removing surface dispersed dyes by alternative, less-pollutant, and more efficient processes have been proposed. These alternative processes include surfactants, enzymes, and other reductants, oxidative clearing, plasma, electrochemical methods, and the application of easily clearable synthesized dyes. Each of these proposed processes has its own pros and cons, and they have special needs. In the present review paper, various processes of clearing surface dispersed dyes from the dyed polyester fibres are investigated and compared with the traditional reduction-clearing process.</em>

Rhodium element is a noble and expensive metal used in many decorative and sometimes engineering works. In this article, the important aspects of rhodium element electroplating have been discussed. The various baths used in the rhodium electroplating process have been described. Also, the effect of some parameters such as current density, temperature, pH value and effect of plating time on the deposition rate and the quality of created coating has been investigated and compared. These studies show that the optimal bath for rhodium element electroplating is the sulfate; which is obtained on the copper substrate at a current density of 8.55 mA/cm2</sup>, temperature of 60 </em>℃</em>, pH=2 and plating time  of 20 min.

According to the new findings of scientists, millions of tons of waste from plastic materials enter the oceans every year. Accumulation, decomposition, and penetration into organisms' life cycle and feed cycle pose a serious threat to the health of humans and the global ecosystem. The production of plastic materials worldwide has increased dramatically in recent years. Any plastic material that is consumed and then enters nature and seas as waste may be divided into many pieces and pollute the environment. Microplastics are directly transferred to the rivers and the sea through sewage or landfill leachate. Microplastics are bioavailable to organisms due to their small size. Their composition and relatively wide surface have made them suitable for absorbing organic pollutants. This article investigates the characteristics, sources of production, ways of entering and its effects on the environment, introduction and identification-analysis methods of these particles. Among the visual methods, the new method of qualitative and quantitative identification of microplastics using colorimetry with the help of fluorescent dyes has been noticed. 

In this paper, Graphene quantum dots are zero-dimensional nanostructures of graphene whose size is less than 100 nm and contain one or more graphene layers. One of the essential features of these materials is the presence of graphene structure, which brings high crystallinity with a multiple carbon structure of </em>SP2</sup></em> type. Graphene quantum dots have many applications due to their unique structure and shape. This factor has caused various synthesis methods to be proposed for this substance. The present study synthesized graphene quantum dots at low cost and without needing special equipment by the thermal pyrolysis method. For this purpose, the Inorganic source of citric acid was used, and the effect of temperature on the final product was investigated with the help of infrared spectroscopy, and photoluminescence tests. The results showed that with increasing temperature, the size distribution of the synthesized particles became wider. As a result, the luminescent properties also changed, and the contribution of green light emission increased. The temperature of 220°C was determined as the optimum temperature for synthesizing quantum dot nanoparticles with blue emission.</em>