In the last post, we discussed the quantity of alum necessary to marble with watercolor and acrylic pigments on paper. There is another class of pigments that can be used for marbling, and was historically an important source of particular hues. These are lake pigments, made from natural dyes. As both a marbler and a natural dyer myself, these pigments are of great interest.
What are lake pigments?
Natural dyes (with the exception of vat dyes including indigo) are water soluble. This means they cannot be used for marbling, as they simply dissolve into the size. In order to make these beautiful organic colors, many of which have no counterpart among mineral colors, useful for marbling they must be converted into pigments. A lake pigment is made when dissolved dye is precipitated onto an inert substrate - often potash alum. The precipitate is then filtered, washed, and ground. For marbling it can be mixed or mulled with a binder, usually watercolor medium, and used like any other watercolor paint.
If you've ever used the all-in-one dyeing method of mixing mordant, dye, and fiber in one pot, you may have noticed some of the dye spontaneously settling to the bottom. This means the dye and alum have bonded together, making a lake pigment.