The Purple Snail

The purple snail, Purpur lapillus, lives along most European coasts (Figure 11.2). It is so called because it hasagland containing acolouredjuice.Thejuicesmells bad, but after painting with it in full sunlight, a purple colour appears after ten minutes that is clear,

11.1

The woollen fibres of a sheep can be used as the main ingredient in paper, sealing strips and thermal insulation. The bones, milk and blood can form the basic materials for bioplastics and binders in glues and paints.

11.1

The woollen fibres of a sheep can be used as the main ingredient in paper, sealing strips and thermal insulation. The bones, milk and blood can form the basic materials for bioplastics and binders in glues and paints.

Materials of animal origin 183

11.2

The deserted shell of purple snails.

11.2

The deserted shell of purple snails.

beautiful, 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. The surviving snails are threatened by pollution from organic tin compounds used in some PVC products and the impregnation of timber.

In principles, the use of animal products has similar environmental impacts to the use of plant products, both being primarily renewable -but conditionally renewable - resources. Climate change may seriously affect their renewability in some cases. For example, more acidic oceans will change the conditions for lime formation in corals and shells.

The amount of energy used for production of most animal products is relatively small; durability is usually good and the materials are easily decomposed assuming no problematic additives. The level of pollution is low. An exception is products from sheep and cows. Where sheep and cows mainly graze on chemically fertilized pastures, this implies quite high energy use as well as the release of eutrophicating substances. Their digestive tracts will also produce and release large amounts of the highly potent greenhouse gas methane throughout their lifetimes. It is thus not environmentally acceptable to raise these animals primarily for the production of building materials. Normally, however, their primary purpose will be to produce meat and milk. Waste wool and similar by-products will therefore not be 'charged' with the climate emissions.

Protein substances can cause allergies in sensitive people. These substances can be released into the air when moistened, and internal use of such paints, glue and fillers should be limited to dry places. It has also been noted that casein mixed with materials containing cement, e.g. in fillers used to level floors, can develop ammonia fumes.

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