Pigment

Traditionally, fresco painters used a limited number of "earthy" pigments, mostly oxides of metal, to create a wide spectrum of colors. One of their common traits is they are not destroyed by the caustic lime putty, which will burn through non alkali resistant colors. Artists should also consider using colors that are light fast. In this regard, it is convenient to stick to traditional colors as they have proven to be both lime and light fast. 

Traditional Pigment List:

• Vine Black,

• Mars Black

• Red Ochre

• Venetian Red

• Burnt Sienna

• Raw Sienna

• Yellow Ochre

• Mars Yellow

• Terra Verte 

• Viridian Green

• Cobalt Blue

• Bianco di San Giovanni (white)

In addition to the pigments listed above, a wider range of colors are used, but there are differing opinions on the unique problems of some pigments. For example, Ivory Black is used by some frescoists while others claim that it will effloresce. Ultramarine blue is easily damaged by acids. Many artists will test pigments in a jar of lime water to verify their ability to be lime proof. Light fastness may be tested as well, however, as with some lime tests, it's hard to determine how these colors will be effected over longer periods of time. 

As you might expect from their name, Sinopia Pigments sells traditional fresco pigments and other colors that are claimed to be "stabilized" for fresco.

Grinding Pigments:

Dry (powdered) pigments should be considered hazardous during handling. Take proper precautions to ensure your safety. Be sure to wear gloves and and a respirator when handing powdered pigments. I recommend reading the Materials Safety Data Sheet for pigments prior to using them. 

The goal of grinding pigment isn't to grind the material smaller. It is to work the pigment into a state of watery suspension. The finished paint will look glossy and have a distinct body different than pure water. It's believed that properly ground fresco pigments are more successfully incorporated into the wall.  Although, it's important to note that it's not a practice shared by all fresco painters. Many mix dry pigment and water on their palette with a paint brush as they are painting. 

Put a manageable pile of pigment in the center of a clean glass sheet. Make a small volcano-like indention in the center and fill it with a small amount of distilled water. Grind the pigment by moving the muller in circles, while gently twisting your wrist back and forth. Continue adding water as needed using a small cup or spray bottle, and be sure to scrape stray paint back to the center of the palette. 

Tip: using a spray mister helps add water more evenly 

Different pigments behave differently in the grinding process. They may seem more or less slippery. Some require a great deal of grinding, while other seem finished after a couple minutes. A great way to test how well the pigment is suspended is to put a finger tip into the paint and then into a clean cup of water. If the pigment floats at the surface of the water, or has a noticeably slow sink, then you've reached a well ground state. 

Notice how the black paint floats at the surface of the water.
Some pigment particles have begun slowly sinking to the
bottom, which is normal.