BLEACHING AND SULPHURING
In bleaching, both oxidative and reductive bleaches can be used on the plant material. While
the former tends to breakdown the coloured compounds, the latter tends to modify them into
colourless compounds (Dubois and Joyce 1988)
In sulphuring, sulphur dioxide acts to bleach coloured (for example, green) plant material and
below a certain concentrations, to fix red colours in some flowers. Colour fixation is associated with
acidification of the tissues. Sulphuring of fresh material is achieved by burning sublimed sulphur
powder (for example. 10g/m3), or by injection of sulphur dioxide gas (1-3 per cent) into a sealed
chamber. The plant material is usually treated overnight prior to ventilation of the chamber and
subsequent completion of the drying process.