As the substances involved in this process are relatively harmless we simply use any leftover liquid to water our garden. Occasionally high PH levels may need to be neutralized with vinegar.
Some materials (like onion skins) can be quite difficult to obtain in large amounts and so to make the most use of the extracted pigment we make what is typically called a “lake” by adding potassium alum and soda ash directly to the exhausted dye-bath. The alum bonds to any remaining pigment molecules and transforms into an insoluble state in an alkaline solution. The alum-pigment molecule then very slowly sinks and collects at the bottom of the container. The liquid on top of the accumulated pigment is siphoned off, fresh water is poured back into the container and the pigment is allowed to sink and gather at the bottom once again.
By repeating this process we can obtain a very pure and concentrated pigment that is free from impurities. This typically takes three to four days, at the end of which the accumulated pigment is filtered through a coffee filter, dried and stored in an air-tight container. In this form it can be mixed with a binder and used for watercolor painting or applied as a wall plaster.
We are currently working on applications that involve brushing this highly concentrated pigment through stencils onto fabric to create finely detailed designs.