When white light, coming from the sun or another light source, strikes an object it is then reflected back to our eyes by that object. Different surfaces absorb, reflect and mix light differently due to their structures and this is why we see different colours. So in painting, different pigments on the surface of the canvas are able to do the same. There are 3 different properties in colour:
1. Hue: or the colour itself e.g. Blue, red, yellow
2. Value: or else the darkness or lightness of colour and this is what creates contrasts
3. Intensity or tone: pure colour comes from the tube but it is rarely used as pure and so it has to be mixed.
There are 3 primary colours from which all the other colours can be mixed… Yellow, red, blue
Tertiary colours are those mixed from two of the primaries e.g.: blue + yellow = green
Colours are said to be either warm or cool. Red is warm while blue is cool.
However there are warm blues (e.g.: ultramarine blue) and even cool reds (alizarin red).
Using cool colours for early morning scenes as well as for winter scenes while warm colours are used for afternoon or summer/Autumn scenes.
Appropriate use of warm and cool colours in a painting will give you depth and perspective, that is using blues for distant objects such as distant mountains and warm colours for foreground objects.
The darkness and lightness of colour will give contrast and hence also useful for perspective. White is the lightest colours while black is the darkest… however black is rarely used in a painting as it is too strong (use Payne’s grey instead). The addition of white to a colour will create a tint. Always keep an abundant amount of white available to use. Colours are usually darkened with a grey to create a tone. The addition of white or greys will affect the intensity of the colour. Adding black will create shade.
Suggestions applicable for oil painting
Always use artist quality oil paints (these contain more pigment and so do not fade when mixing). Also it will be easier to create texture when using knife for painting. You cannot work well with runny colours.
If oil colours are too thick then thin them with turpentine or linseed oil, only to a creamy consistency. The more oil you add the more time it takes for the painting to dry. Turpentine is usually added to colours used for the underpainting to encourage fast drying.
Add more oil to the top layers of a painting as these has to dry the last, known as FAT over LEAN. The painting can crack if the upper paint dries before the lower one. Always paint in adequate ventilation as oil colours are toxic even if they do not smell. When starting painting, start from very dark (usually monochrome) underpainting, just indicating the basic shapes and structures and light/dark areas. Always keep in mind that there is no light if there is no darkness and so you have to create contrast by putting highlights over darker areas. I will give more details how to use colours when talking about landscape painting.
You can paint on any type of surface as support such as paper, wood panels, metal etc. For oil painting the most commonly used is canvas, either stretched or unstretched. You can buy canvas either in roll or ready stretched, however buying a roll will turn out to be a cheaper alternative. You can buy this canvas either already primed or unprimed. The primer acts as a base for the oil (or acrylic) paint to adhere to without cracking, peeling, wrinkling or shrinking. The most commonly used primer is gesso and it can be applied either as a single layer or double layer.
There are different types of canvas of which cotton is the most commonly used. The other type is linen that is very expensive. It is important to use good quality canvas and this usually has to be of a minimum of 10oz and 12oz for big paintings. Ready-made canvases found in stores are barely 8oz and even less. If you buy canvas by roll you can have a better quality canvas with the same price that you buy a similar size but of an inferior one from a store.
Brushes, Knives and Palettes
For oil and acrylic painting it is very important that you buy good quality brushes. Inferior brushes will start losing hair while painting and it is really annoying to stop every minute to remove hair from the surface of your painting. Do not buy synthetic ones but only buy those having natural hair such as hogs hair. Brushes come in various shapes and sizes. You must have a selection of round, flat, filbert, fan and liners (for fine and delicate work). You must also have a selection of sizes usually numbered from 0 to 12 (12 being the largest). Different brushes are used for various techniques. A good brush must maintain its shape when being used. You must also have a 2 inches brush for background colouring (and underpainting), that you can buy from an ironmonger (also used for house painting). The most important is to clean the brushes while using them and after you finish as if you do not do so then you will end up wasting money. While painting you have to clean the brush before picking up colour and this is done using tissues. Do not clean the brush with turpentine while painting. When you finish first remove excess colours using a tissue and then clean the brush in turpentine followed by rinsing it in water with a dishwashing detergent. Do not throw away old brushes as you might find them useful to create certain effects.
Painting knives are used to mix paints on the palette as well as to paint, usually very useful to lay thick layers of paint onto the canvas and to create structures like tree trunks and rocks. You can also use them to create fine but straight lines, snow caps on a mountain top or to create small waves on a water surface. Same as brushes, painting knives come in different sizes and shapes. Always clean your knife before picking up colour from the palette.
Use a flat palette for oils and acrylics as it will be very difficult to pick up paint from palettes used for watercolour. You can have a wooden or a Perspex palette, or even simply a disposable plate. Alternatively you can use a tear off palette, which is very useful and you do not need to clean it afterwards.
Paints and diluents
Always use artist quality paints for both oils and acrylics. Artist quality paints have more pigments rather than binders. Artist quality paints do not fade away when mixing and also they will last longer. Artist quality oil and acrylics are usually heavy bodied and thus easier to paint using painting knives.
When painting with acrylics, paints are usually diluted to a creamy consistency with water. To increase drying time you can use one of the many retarders that are commercially available.
Turpentine is usually used to dilute oil paints for underpainting to decrease drying time. Try to use odour free turpentine especially when working indoors. Oil colours can be diluted with linseed oil for upper layers of a painting, thus increasing drying time. Poppy oil is another diluent that can be used to dilute oil paints. The more oil you add the more you increase the drying time. The consistency of the paint should be creamy and should be in a way that the paint is easily released from the brush onto the previous layer. Liquin is another excellent medium that decrease the drying time of oils and is very good for glazes.
Varnishes are used to protect the painting and colours from deteriorating with time besides making it easier to clean. There are two types, matt and gloss. Matt varnish does not reflect light and hence will give uniformity to the painting, since oil paints have different glare when dry.
Allow the painting to dry well ideally about 6 months. You can apply varnish either using a brush or using aerosol spray. To apply the varnish lay the painting horizontal on a clean surface (dust free) and apply onto the surface in a uniform manner. Apply in a well-ventilated place or outside, and beware of any flying insects that can rest on it accidentally. Matt varnish can sometimes form a cloudy appearance after drying sometimes affected by humidity.