My oil painting technique for detailed portraits

The technique I use, particularly for pet portraits, is based on that employed by many of the great masters including Rembrandt, Michelangelo Buonarroti and Turner. The process is quite a long one, with a lot of drying time, so GRIFFIN ALKYD oils are used. These are a fast drying oil paint.
First, the composition is tranferred to the canvas as a charcoal sketch. This is done using a grid system. The original is divided up into squares, the canvas is then divided up into the same number of squares. The image is then carefully copied to the canvas paying particular attention to the areas of light and shadow, these areas are outlined in the sketch.
Once the drawing is in place, the underpainting can be done. This is a monochromatic layer which establishes the shadows and highlights and a certain amount of the detail. Typically Paynes Grey is used for this, though terre verte is also sometimes used.
With the underpainting done, the next step is to bring some colour to the picture. This is done through a number of thin glazes of colour over the underpainting. This can take quite a while as each layer has to be dry before the next can be applied, up to 20 layers can be involved to get the richness of colour required. As the glazes are applied, the details are added or re-established until the final painting is complete.