Oil Paint brushes we use in our Melbourne art school vary a lot in quality and shape however they are all made from bristle (a strong tough fibre either synthetic or hogs hair) unlike watercolour brushes which are made with a much softer sable hair.
The most common brush shapes are filbert, flat and round. They also come in other shapes like fan and angular chisel. I’m very reluctant to use these because I consider them a bit of a gimmick although some of my students at Art Makers Studio Gallery sneak one in occasionally.
I like to use Filbert brushes which are flat brushes with rounded and tapered corners shaped something like a finger nail. My general range of sizes are No’s 2, 4, 6 8 10,12
Filberts generally do not come in the range of cheap brushes as do flats which have a chiseled straight cut edge or round brushes which are in the round like a mop.
Brush size depends on the size of the shapes required in the painting eg. A No. 2 would be used for a relatively small area and a No. 10 on a much bigger area. With a good quality filbert brush it is possible to do very fine lines even with a No. 6 or 8
For very fine detail I would sometimes use a 0 or 00 round brush.
I use large flat brushes for the preliminary washes These are relatively cheap around $8 for size 10 and do the job quite well.
To clean the brushes I use Mineral Turpentine and sometimes Petroleum Jelly and Baby Oil for especially stubborn grim hardened at the base of the brush. I use a tradesman paint cleaning tray which is a metal box about 30x40cms with a sturdy wire grate which sits on an angle with one end resting in the mineral turpentine. When I paint outdoors, I use a glass jar with a stainless steel pot scourer in the bottom
The number of brush required for a painting varies according to the complexity of the painting with different colours on each brush or though sometime one brush can hold more than one colour and can be utilized to scumble (turning the brush over and over taking the paint off as it turns) and mix the paint on the canvas.
Holding the brush. This is a very important part of painting. The relationship between the painter and the brush. The idea is not the strangle the brush by holding it too tightly nor hold it like a pencil. It is not a pencil and the painting strangely will always look like a drawing in paint. Drawing is not our aim. Hold the brush as if it is an extension of your hand with the hand over brush held between the the thumb and the index finger.
For straight lines press the brush firmly on the canvas until the hand is steady and not shaking. Pressing down make a mark at the beginning of the line now lift the brush and make a mark at the end of the line in the same firm way, now mark another mark about 5cm long in the middle between the two marks. Each time holding the breath.