Animal proteins consist of both fat soluble (hydrophobic) and water soluble (hydrophilic) compounds, and are therefore well-suited for use in emulsion paints dissolved in water. The products are not especially strong, but usually highly permeable to vapour and are thus suitable for interior use on ceilings and walls. There are mainly two types: collagen glue paint and casein paint. Collagen glue paint is based on waste from abattoirs; casein paint is based on milk.
In buildings, under dry conditions the products are inert and do not lead to electrostatic charging. In combination with damp cement, protein glue paint can emit ammonia that can irritate the respiratory system. Long-term dampness can easily lead to attacks by fungus and other bacteria. The bacteria break down the protein, and the rotting products emit a bad smell and cause irritation.
Waste from this type of paint can cause the growth of algae in streams and rivers. Animal glue paint and casein paint can normally be washed off painted materials, so the materials can be easily prepared for re-use. Painted materials can normally be composted or burned in conventional incinerators.
Collagen glue paint is good for using on dry interiors on masonry, wood, hessian and paper. The surface has to be cleaned of any fats before painting; otherwise a small measure of sal-ammoniac can be added. Its opacity is good, and many pigments can be used. Though the paint is not water proof, experience shows that washing down an animal glue painted wall and applying a new coat is no more work than meticulously cleaning a wall painted with a stronger paint. Animal glue paints can also be used in emulsions, usually with linseed oil. This produces a water-repelling paint.
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