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Asked by benmck to Angela, Gabriele, Karen, Maria, Shane on 11 Nov 2013.
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Karen McCarthy answered on 11 Nov 2013:
Good question! Well there are two main ways that paint is made, therefore two different drying processes.
If a paint is water-based, and water evaporates, then when paint is on a wall the water is free to evaporate off, leaving the coat of solid paint.But while the paint is in the tin, it is under pressure from being sealed in the tin so evaporation cannot occur, therefore the paint stays wet and liquid.
However if the paint is oil-based, then drying takes much longer because the drying process is based on a chemical reaction between the paint and oxygen in the air. Because the tin has been sealed, when the paint is in the tin there is no oxygen available and again thats why it stays wet and liquid!
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Shane Mc Guinness answered on 11 Nov 2013:
Perfect answer Karen! In some paints it also has to do with some very cool chemical changes called oxidation. This is where oxygen atoms bind to the paint molecules and make them harder. The paint on cars involves this for example, which is also why pouring acid on these paints removes them as it may reverses the process!
Oil based paints also contain “volatiles”, which are oil-based chemicals which evaporate very quickly meaning the paint dries quicker, and which is exactly why some paints smell so badly. It’s also why some paints are flammable and why petrol in your car is dangerous! -
Angela Stevenson answered on 12 Nov 2013:
Excellent answers Karen and Shane! It’s really interesting how the drying mechanism of paint tells us a lot about its formulation of acrylic, watercolour, oil, and other paints. Great question!
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