Silk shading is a beautiful technique, also known as 'thread painting' or 'painting with the needle'. It boils down to just one stitch, 'long and short stitch' with split stitch in a supporting role.
Silk shading allows the embroiderer to depict their subject in a natural way, using the flow of the stitches to enhance the flow of fur or the smooth lines of a petal, and creating gradual changes of hue and shade.
Traditionally worked in silk threads, this technique is most often taught now with stranded cotton because it has had the widest range of colour. In my teaching I use a range of threads, from stranded cotton to the thick floss silk which would have been used centuries ago. Using the wide variety of threads available allows the embroiderer to scale the stitches according to the size of the finished work.