Madder pigment (left) ground madder root (right) from rubia cordofolia.
Commonly used in converting natural dyes into pigments. A pigment made from a natural dye is known as a "lake".
The dyebath is strained to remove all the ground madder root. Alum and a base (calcium carbonate or potassium carbonate) are added. A precipitate begins to form.
Close up ...
A hand-pump makes the filtration go faster.
On the cloth filter.
The traditional way.
The finished lake on the left, the original powdered madder root on the right.