After years of answering "Sorry, I don't know" to enquiries generated by the Countryside Museum's mention of "Dolly blue" I have finally found out what went into it. I recalled that my grandmother referred to packets of "Reckitt's Blue" in her "armoury" although the label read "Reckitt and Colman". I searched on the names, and here is part of what came up:
This laundry starch company began producing laundry blue in 1852 by using a combination of a synthetic ultramarine and sodium bicarbonate. The advent of using this synthetic made the product affordable to the masses since the active ingredient was previously made by grinding the semi-precious stone lapis lazuli.The naturally occurring blue pigment found in lapis was first discovered to be sodium aluminosulfosilicate in 1824 by the French chemist, Jean-Baptiste Guimet. Guimet realized he could synthesize ultramarine by combining china clay, soda ash, and trace sulfur. (http://www.frankjump.com/002.html)
This dye used to be made near Backbarrow in the south of the Lakes, and the factory was known as the "dolly blue works". The rocks along the riverside there became covered with a fine, royal blue dust from the works.
Dolly Blue was made from China clay, Caustic Soda, Sulphur, Pitch and other substances and then was ground before being baked in kilns. The "Raw" Blue was washed and processed to make Dolly Blue, added to synthetic rubber, paints and other products. I worked there on shifts for a short time in the early sixties. The site of the old factory was formerly a dark satanic mill where the labour was provided by orphans from Corner House Liverpool.
Mike - Dalton in Furness