Ascorbic acid treatment to improve the light fastness or as reducing agent on silk fabric dyed with pulverised natural dyes

Purpose – This study aims to improve the natural dyeing recipe with better light fastness using ascorbic acid (vitamin C) with pulverised plant dyes. Design/methodology/approach – Silk fabrics pre-mordanted with alum (aluminium ammonium sulphate) were dyed using six types of plant dyes available in Sarawak, Malaysia, namely, Engkerabai leaves (Psychotria viridiflora), Ketapang leaves (Terminalia catappa), mangrove bark (Ceriops tagal), Sepang wood (Caesalpinia sappan), mangosteen husk (Garcinia mangostana) and onion skin (Allium cepa). Then, the dyed samples were immersed in vitamin C. The dyed and vitamin C-treated silk samples were exposed to direct sunlight for 40 h to test whether vitamin C had any effect on the light fastness of the dyed samples. Findings – It was found that the fabric samples using vitamin C for after-treatment, particularly Engkerabai, Ketapang, mangrove and mangosteen, exhibited better light fastness. The colours of the four samples changed and looked darker when compared to the non-treated fabric samples. However, it was observed that vitamin C had a reverse effect on Sepang wood and onion skin. The acidic aqueous solution of vitamin C discharged the dyed samples instead. Originality/value – In conclusion, depending on the plant types, vitamin C can be used to improve the light fastness of natural dyes or as a reducing agent for natural dyes

A Study of Soluble-Powdered Natural Dyes

This paper highlights an on-going study that produces soluble-powdered natural dye extracts from Sebangki barks (Neesia spp., Bomb.; Tristaniopsis spp., Myrt.), Engkerabai Paya leaves (Psychotria viridiflora Zoll. ex. Miq.) and Engkudu roots (Morinda citrifolia L.). These three natural colourants are typically used by the native Iban community in Sarawak to dye silk threads for Pua Kumbu weaving. The two primary objectives of this study are to convert natural dye extracts into soluble powder using solvent extraction and to formulate textile dyeing recipes with good colourfastness and lightfastness using powdered natural dyes extracts. The successful experiments show that distilled water and ethanol can be used as solvents to extract natural dyes from Neesia spp., Bomb.; Tristaniopsis spp., Myrt. barks, Morinda citrifolia L. roots, Psychotria viridiflora Zoll. ex. Miq. leaves. In addition, it is proven that the method of freeze drying is capable of converting liquid dye extracts into soluble powder

A multi-country analysis of the 2007–2009 financial crisis: empirical results from discrete and continuous time models

In this article, we provide empirical evidence of the recent financial crisis over 2007–2009 using discrete time multivariate GARCH (MGARCH) models and continuous time modelling approaches. Using daily data for 14 countries, we investigate the return and volatility spillovers among the US and other international markets. The MGARCH results reveal positive return spillovers from the US to a number of markets, and volatility transmission is verified. The US market is prone to return and volatility transmission from a limited number of markets. The continuous time analysis finds evidence of feedback effects in some cases. Evidence shows that spillover effects intensified during the financial crisis