Normally, thangkas are painted on a fine grain cloth such as cotton or silk - 'Western' canvasses are too rough to enable the fine detail to be drawn and painted in. To prepare the painting surface, the cotton is stretched out in a frame and then a coat or two of 'gesso' ( thick white or off-white paint that is simply ground chalk and a glue binder) is applied to both sides of the cloth. This can be sanded smooth once dried to give a surface that is suitable for drawing upon and to accept paint.
The line drawing is either drawn directly onto the ground or can be transferred on by different methods such as tracing, firstly in pencil or charcoal which is then inked in using waterproof ink to make it more permanent. A thin coat of gesso may be applied over the line drawing to tone down the ink lines and to provide a little 'tooth' (a slight roughness) so that the paint will adhere better to the surface.
Paints are then applied usually in the order of painting the most distant objects first and then moving 'forwards' in the composition. For instance, a typical order might be - sky, clouds, hills, water, body and head auras then the figures themselves. This is so that 'closer' objects overlap those behind. There is also a consideration of using as much of one colour at one time so, for example, the water may get painted at the same time as the clouds because they use the same paint.
Coats of colour are laid down first either as flat colours or using techniques of 'wet-blending' that provide a colour graduation. These may then be shaded using darker paints to build up a 3-D effect known as modelling. It does not necessarily produce the effect used in western art of realistic directional lighting and shadow. The modelling used here is merely to give the illusion of rounded-ness and 'body'.
One thing that sets these paintings apart is the use of 'Tibetan' gold. This is a pigment made entirely of powdered gold produced in a secret process by a group of highly skilled craftspeople in Nepal that has never been successfully recreated. A company in London produces a version of this paint, the quality and fineness of which is nowhere near that of the traditional gold paint from Kathmandu.
The gold paint is applied to many features both on the deity (eg. necklaces, earrings etc), to landscape features such as rock outcrops and trees, and to flame auras, thrones and lotuses among others. Some thangkas use extensive gold outlining (see thangka of Vajrayogini in the gallery) to almost every object in the composition, and there are also so-called 'gold' thangkas that are entirely gold with the figures 'drawn' on merely in outline form.
Each object in the painting is then outlined using dark colours such as indigo (used to outline blues and greens) and lac dye (a dark brownish red used to outline reds, oranges and yellows). Much of the skill of the painter can be measured in the fineness of the outlines he or she produces. It is this aspect that brings the painting alive with its use of varying line thicknesses to produce an illusion of movement, depth and character.
After burnishing the gold, painting in the eyes (always left until last) and inscribing the sacred letters and dedication of the back of the painting, it can be cut from the frame and mounted either in a traditional silk brocade or framed in a more western style frame depending on the wishes of the patron.