1. Indigo Dye and Blue Used in Japanese Paintings in Opposite Ways
Indigo, used to dye cloth blue, works by having its colorant enter the inside of the fibers to create color. On the other hand, the blue used in Japanese paintings is made from crushed minerals like azurite or lapis lazuli, which sit on the surface as grains. [6]
The first is a dye; the second is a pigment. One way to tell them apart is to see if they dissolve in water or oil. [1] [2] However, there is an exception to this rule. The reason why indigo, which does not dissolve, is used as a dye will be explained in a later section.
2. Why Dyes Must Stay Stable Through Washing and Sunlight
Dyes are colorants that have been used to dye natural and synthetic fibers by dissolving them in a liquid. They need to resist washing, sunlight, friction, and sweat. [2]
Many natural dyes do not easily stick to fibers on their own. They rely on help from mordants, such as iron or alum, to develop color and set firmly. For example, using alum (aluminum) as a mordant can produce a vivid red from madder or sappanwood. Combining this with iron mordants can create shades ranging from purple to dark red. [2]
Dyes are colors that dissolve and enter the cloth. So, what is different about pigments?
3. How Pigments Use Glue to Attach Insoluble Grains to Surfaces
Pigments are powders that do not dissolve in water or oil. They color objects by being dispersed in a powdered state. [1] Since the grains do not dissolve and enter the fibers, paints mix them with a medium (called a binder), which acts like "glue," to attach them to the surface. [3]
Grains generally have a strong ability to hide the color underneath, which is called opacity. Dyes tend to be transparent. [1] However, some dyes can also be opaque. Pigments include inorganic pigments made from mineral powders or synthetic materials, and organic pigments, which have vivid colors and strong coloring power. [1]
Pigments tend not to fade in sunlight, while dyes tend to fade easily under ultraviolet light. However, there are pigments that fade easily, so exceptions exist. [3] If color is applied by grains, does the size of the grain matter?
4. Why Grinding Gunjo Powder Finer Makes Whitish Byakugun
For Japanese paintings, gunjo and byakugun use powdered azurite or lapis lazuli as raw materials. The smaller the grains, the lighter the resulting color becomes. [6] Even from the same raw stone, the shade changes depending on the grain size.
Blue stones were once very expensive. The pigment gunjo made from lapis lazuli was extremely costly in Europe. The name "ultramarine" is said to come from the Latin "ultra marinum" (beyond the sea). [5]
In the 1820s, France encouraged development, and artificial ultramarine was created. [5] Sources vary on the exact year between 1826 and 1828, but it happened around this time.
We have looked at pigments made of insoluble grains. So, how can an insoluble pigment become a dye?
5. How Insoluble Indigo Becomes a Dye
The blue colorant in indigo is called indigo; it is a dye that does not dissolve in water. When treated with a reducing agent, it becomes a pale yellow water solution called "indigo white." [4]
If cloth is soaked in this liquid, the indigo white enters the fibers. When taken out and exposed to air, oxidation occurs, and it returns to the original blue indigo, resulting in blue-dyed cloth. [4]
This means that even an insoluble colorant can be used as a dye if it is temporarily in a soluble form during the dyeing process. The axis of "dissolving vs. not dissolving" alone cannot fully explain indigo.
So, can a soluble pigment be made into an insoluble form?
6. How Making Dyes Insoluble Turns Them into Pigments
Pigments made by turning water-soluble dyes into insoluble forms, such as calcium or barium salts, are a type of lake pigment. For example, there are "azo lake pigments" made by making water-soluble azo dyes insoluble. [1]
Soluble dyes can be used as pigments if they are made into an insoluble form. Therefore, the boundary between dyes and pigments is determined not just by the type of pigment, but by how it is used—whether it dissolves or not. However, not all dyes can be turned into pigments; this applies to only some types.
In the case of indigo, an insoluble blue was temporarily dissolved. In the case of lake pigments, a soluble color was made insoluble. Both change the usage along the axis of "dissolving vs. not dissolving."
7. An Experiment: Testing Water-Based Pens with Water
Get a few water-based pens and draw lines on white paper. After they dry, drop one drop of water on the end of a line. You should find some pens where the color spreads and some where it does not. [1]
The difference in how the color spreads may be related to whether the colorant dissolves easily in water. However, this method cannot determine if the pen's color source is a dye or a pigment. Use what you observe as a starting point for asking, “Why?” [6]
If you want to read more, try opening the entry for "byakugun" in the Dictionary of Japanese Art Terms or the explanations from paint manufacturers (in English). [6] [3]