With pochoir, a hand painted fashion plate, or illustration to be duplicated was carefully analyzed to determine each colour layer. Often, but not always, an outline of the image was printed as a black and white lithograph and served as a base layer, especially in the design and fashion portfolios. Each succeeding layer of colour was then printed over the black and white litho layer. Depending on how intense the lithograph layer was, it would either be incorporated fully in the final image or be invisible and serve only as a guide to the image layout. Separate stencils were cut, sometimes in thin sheets of copper, zinc, or aluminum, for every color component. Later stencil materials were made of celluloid or plastic and contemporary stencil materials are made of coated paper or acetate. Each successive colour layer, using watercolour or gouache, was applied to the stencil with a brush called a pompon. Pigment on the brush could not be thick or runny, as paint could easily slide underneath the stencil and change the shape of the image. Therefore, it was necessary to really blot the pigment on the brush before applying it to the stencil and in the case of watercolour images, this was even more critical. Skilled printers could achieve incredibly subtle details using gradation and stippling, spattering or even simply drawing additional details with a small brush on the final layer. Sometimes as many as 100 stencils were used to recreate a single image, and the resulting print was surprisingly rich and detailed