Civil Engineering Reference
In-Depth Information
The purple snail
The purple snail,
Purpur lapillus
, lives along most European coasts. It is so-named
because it has a gland containing a coloured juice. The juice smells bad, but after paint-
ing with it in full sunlight, a purple colour appears after ten minutes which is clear, beauti-
ful, durable and does not fade. A huge amount of snails are needed for the smallest
amount of decoration. The development of this colour technique occurred in the eastern
parts of the Mediterranean after the Phoenicians settled, about 5000 years ago. In Asia
the purple painters had their own workshops at the royal courts, and purple became the
colour of the rulers. The snail was worth more than silver and gold, but with the rise and
fall of the Mediterranean empires almost the whole population of snails disappeared.
Today the purple snail is no longer considered a resource, as the surviving snails are
threatened by pollution from organic tin compounds used in some PVC products and the
impregnation of timber.
The use of animal products has the same environmental impact as the use of
plant products. They are renewable resources and the amount of energy used for
production is relatively small; durability is usually good and the materials are
easily decomposed. The level of pollution is low, but factories producing animal
glue do smell if there is no appropriate cleansing equipment.
Protein substances can cause allergies in sensitive people. These substances
can be released into the air when moistened, and internal use of paint, glue and
fillers should be limited to dry places. It has been noted that casein mixed with
materials containing cement, e.g. in fillers used to level floors, can develop irri-
tating ammonia fumes.
