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The Colour Purple

An Essay on Colour in Fungi

During the reign of Julius Ceasar in Rome, the only people allowed to wear purple (Tyrian or Royal purple) were the Emperor and his family. The colour was difficult to obtain, initially because the dye came from glandular mucus of the shell-fish Murex brandaris and M. trunculus from the Mediterranean. Thus wearing clothes dyed purple indicated great wealth and power. When Roccella, a readily available lichen, was found to provide the colour purple, the use of purple became more widespread but it also declined in popularity.

A purple dye produced by Roccella was reintroduced during the 14 th century in Florence. It was known as orchil, a corruption of the family named Oricellari, who manufactured the dyes. During the 18 th century, another lichen Perusaria was used to produce a purple dye.

Symbolism and ritual were strongly associated with the use of dyes. Colouring the clothes and body constituted an important component of the display. Indeed, while the main trade between Central America and Europe after the Spanish conquest was in minerals, the export of natural dyes was an important second. However, the use of lichens as a source of dyes for cloth has declined. Huge quantities of lichen are needed, often as much as the cloth. From the mid 1800s synthetic dyes based on analine from coal tar were used commercially. Use of synthetic dyes has dominated the dying industry since then.

tweed
Photo of a drab Harris tweed jacket.

Dyes based on fungi, especially lichens, have been used for a long time. While an enormous array of colours may be found among the living fungi, most degrade rapidly. The most common colours obtained from fungi are the browns, yellows and greys. These colours are typical of the tweeds of Scotland. Indeed, some Harris Tweeds still require crottle (lichens). The colours of the pH indicator, litmus, and various reds, yellows and mauve are also available especially when using appropriate mordants (fixatives that may also modify the colour). Litmus is a dye also obtained from Roccella. In alkaline conditions it is blue. As the dying conditions became more acidic, the colour changes from blue to purple and then red. These colours can be fixed to the cloth by using an appropriate mordant. Interestingly, alkaline conditions were originally obtained by using ammonia from urine. The urine was kept in a “lake” in which the cloth was dyed. To obtain purples and red, the lake was heated to drive off the ammonia. No doubt the smell was the main reason lakes were maintained away from the houses of the rich. None the less, fungi are a potential source of a wide array of colours.

fruitbody
Brightly coloured fruitbody. Image from E and R Kearney

Not all fungi produce an appropriate colour, and not all fungal colours can be used successfully. To date, rather drab lichens and fruiting bodies of some macromycetes have been used as sources of dyes. Most microscopic forms of fungi have not been tested for their staining properties. Because many fungi can become coloured in culture, they may be a useful source of dye, especially if the dye is required in any great quantity. Some fungi form obvious colours in their sporocarp. However, the colours of many fungi change rapidly or fade during extraction, limiting the value of the commercial product. Other fungi have a colour that is unpredictable. The lack of predictability of colour also limits the use of the dye. The search for new dyes among the fungi, and determination of their properties, require a more scientific approach.

The use of fruiting bodies of fungi and thalli of lichens as a source of dyes is limited by their availability. Because the dyes can be extracted from thalli, it is possible that cultures grown under appropriate conditions could become a source of useful dyes. The potential to manage growth conditions during manufacture means that the fungi could be developed for production of specific colours at will. Maintenance of cultures in controlled conditions means that production is commercially more reliable, predictable and manageable. Unless new forms of production of useful dyes are found, fungi will remain a small and unimportant source of natural dyes for use in industry.

The exploration of fungi as natural sources of dyes is increasing largely because of the increasing cost of petroleum products. ‘Natural’ dyes are believed to be safer and their production more environmentally sustainable. LINK While use of natural products is still restricted, some interesting products are being (re) discovered. We cannot go back to the past. Lichens are slow growing organisms; harvesting for a large dye industry would deplete reserves rapidly. New approaches to production of natural dyes are necessary. As many fungal partners of these lichens can be cultured, the biosynthetic pathways underpinning chromophore production may be elucidated and possibly enhanced, either in the original fungus or on transfer to more culturally amenable fungi.

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FURTHER READING

Bessette AR & Bessette AE (2001) The Rainbox Beneath My Feet: A mushroom dyers Field Guide. Syracuse University Press.

Cedano M, Villasenor L, & Guzman-Davalos L. (2001) Mycologist, 15: 81 – 85.

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