Standard formulations for cold dyeing routes of agates: An energy-saving option for artisanal and small-scale producers

Artisanal and small-scale processes of dyeing of agates are usually non standardized and often ineffective. In the Brazilian scenario, local arrangements need actions to improve the current processes and to minimize energy consumption and production of wastes. In this sense, the aim of this study was to investigate new standard dyeing procedures capable of producing a satisfactory color alteration using minimal quantities of inorganic dyes and heat. A so-called cold dyeing route was outlined and tested for the artificial colors black, red, blue and green. In all cases, experimental results showed a significant, and in some cases dramatic, improvement in the final color of agates dyed according to the proposed cold dyeing system in comparison to the conventional warm process. Most important, these improvements were achieved with an average reduction of heat energy and reactant consumption of 94.6% and 56.6%, respectively. Potential benefits obtained from applying the cold dyeing route include the reduction of operating costs and decrease in wastewater burden due to the use of dye solutions of low concentrations under optimized conditions.