Paint Point: Chemistry of Different Kinds of Paints
Art is not possible without chemistry. All types of paint and colours and different mediums that are used in the creation of beautiful masterpieces use chemistry as the backbone. We've used and heard about paints like oil paints, and watercolours but what are paints and how does one form differ from another? So let's start by answering the question-
What is paint?
Paint is a mixture of pigments with a medium or a solvent that can be applied to give colour to the canvas. Pigments are usually in dry form and mixed with a liquid solvent. The reason that pigments have a colour is due to the presence of unpaired electrons in the metal ions. These pigments can be dissolved in solvents that can be oil-based or water-based. Oil-based paints do not dissolve in water and vice versa.
Oil-based paints
Oil-based paints use oils as their medium to dissolve pigment. Oils are triglycerides and differ from fats. Oils are liquid at room temperature due to the presence of double bonds in the fatty acid chains that are joined to the glycerol moiety. The most common oils used are linseed oil, walnut oil etc. Dyes are combined with oils to produce shades of colours. Oil paints come in paint and pastel sticks. Pastel sticks are solidified oil-based pigments and also come in hard and soft textures. Since oil paints don't evaporate they dry by reacting with oxygen present in the air. The absorption of oxygen hardens and dries up the paint.
Water-based paints
There are many water-based paints used by artists like acrylics, watercolours, gouache etc. The one thing they have in common is that they all are soluble in water and use water as a medium for application. These paints use binding agents which solubilise the pigment and are also soluble in water.
Acrylics
These paints have pigments suspended in acrylic polymer solution which solubilises the pigment in water. Methylacrylate is one of the monomers used and these paints are synthesized and manufactured in laboratories. The binders in these paints act as emulsifying agents. These are non-biodegradable in nature.
Watercolours and gouache
Similar to acrylics these types of paints are water-based. These both use a different type of binder, which is gum arabic derived from the Acacia tree. These paints are solidified pigments mixed with binders. When water is added to these, they dissolve in water and stick to the surface. After the water evaporates the pigment dries and sticks to the surface. The difference between watercolours and gouache is the difference in their opacity which is due to the particle size of dry pigment. Watercolours have more transparency than gouache.
Painting is a fusion of art and science. Not only the expression of colour by ions is itself a beautiful phenomenon, but the use of these pigments to create pieces of art is marvellous. Next time you open a paint box, remember the science behind it!
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