The dyestuff content in plant sources is rather low, usually in the order of a few % of the mass of dry plant
material. Introduction of plant dyes into technical scale textile dyeing operations thus requires handling,
extraction and disposal of huge amounts of plant material.
The precipitation of a solid, dyestuff-containing residue by addition of FeSO4$7H2O to the aqueous
plant extract yields a highly concentrated plant dye. In this work Canadian Goldenrod (Solidago cana-
densis) was used as representative case to study production of a concentrated solid plant dye. An iron
content of 5% w/w of the dry precipitate was analysed by photometry (1,10-Phenanthroliniumchloride).
The content of total phenolics (TPH) calculated as gallic acid monohydrate equivalents according the
Folin-Ciocalteau method, was determined with 45% w/w.
The dyestuff precipitate was tested in standard dyeing experiments. Shade and colour depth were
found comparable to dyeings obtained with direct use of plant extracts. Use of a concentrated natural dye
product offers new approaches with regard to standardisation of dyestuff quality, handling and appli-
cable dyeing techniques.