Résumé
Is it pertinent to propose the colours of ancient dyers as an inspiration for today's colour lovers? Is it possible to reproduce their colours, following their recipes or with different ingredients and techniques? To answer such questions, as a case study, we present the first results of our experiments to compare the scale of blues of a French 18 th century dyer [1] with the scales of indigo blues obtained today, using different indigo sources and vat processes. Antoine Janot (1700-1778) was a master-dyer in Saint-Chinian (Hérault, France), a centre of production of wool broadcloth for exportation to the Levant. He has left a Memoir-on the processes of dyeing the colours that are consumed in the Levant in the good and fast mode of dyeing, with the quantities and qualities of the drugs from which they are obtained, dated 31 st may 1744, preserved in the Archives départementales de l'Hérault in Montpellier.It describes dyeing processes for 65 different colour shades, illustrated by 59 samples of dyed wool broadcloth. The first colours presented are the eight degrees of his scale of blues. This scale might have been looked upon as one among many examples of irretrievably lost technical knowledge, the main reason for this being the process by which these blues were obtained, viz. the woad vat, boosted by an addition of indigo pigment Nowadays woad is no longer processed into woad balls or couched woad, except in very limited quantities for workshops of experimental archaeology, while in his Memoir, Antoine Janot describes a large-scale process, in a vat containing several thousands litres of hot water to which are added hundreds of kilograms of couched woad and several kilograms of natural indigo. Could it then be assumed that proportions of ingredients calculated from his description would still be valid for a smaller scale version of the process ? To answer this question and also to propose alternative ways to reproduce Janot's different degrees of blues, expert indigo dyers from different parts of the world have started experiments to reproduce these blues with their local source(s) of indigo and different vat processes, traditional or not, biological or chemical, at different scales. The same quality of fine wool broadcloth was used by all. It presents the same chromatic specifications as an undyed sample of the broadcloth Janot used to dye. Colorimetric measurements of all samples, from the18 th century document and from all experiments, were performed with the same instrument in the same conditions. Research is still ongoing, but experiments already show that blue dyes with the same chromatic specifications as the different gradations of Antoine Janot's scale of blues can be obtained in our time, from biological fermentation vats of different volumes, set with indigo extracted from all the indigo-producing plants that have been used on a large scale by indigo dyers, in all parts of the world. This is a welcome discovery, coming at a time when the production of indigo from all these plants is enjoying a significant revival, which makes the sourcing of natural indigo less and less of a problem.