Calcium carbonate, often referred to as fine French chalk, is a versatile material in oil painting, primarily used for preparing specialized grounds or campituras. This application allows artists to create a unique surface for their oil paints, differing from traditional gesso.
Preparing a Calcium Carbonate Ground (Campitura)
To create a sturdy and adaptable ground using calcium carbonate, you'll combine it with boiled linseed oil. This process transforms the dry powder into a workable, paint-like consistency.
Here are the steps to prepare a calcium carbonate ground:
-
Gather Materials:
- Fine French chalk (calcium carbonate)
- Boiled linseed oil
- A palette knife
- A mixing surface (e.g., a glass palette or slab)
- Optional: Oil paints for tinting
-
Mix the Base: Start by placing your fine French chalk onto your mixing surface. Gradually add boiled linseed oil, aiming for a proportion of approximately one-third boiled linseed oil to the volume of calcium carbonate.
-
Work the Mixture: At first, the mix will appear very dry and crumbly. Using your palette knife, begin to thoroughly work the mixture. Continuously fold, press, and spread the material. As you work it, the calcium carbonate will absorb the oil more uniformly, transforming into a consistency that resembles a heavy paint. This property, where it becomes more fluid when worked and thickens at rest, is known as being thixotropic.
-
Tint the Ground (Optional): Once the desired thixotropic, heavy paint consistency is achieved, you can tint the ground. Add small amounts of your chosen oil paints into the mix. Continue working it with the palette knife until the color is evenly distributed throughout, creating your final colored ground, or campitura.
This prepared calcium carbonate ground provides a unique foundational layer for oil painting, influencing the absorption and handling of subsequent paint layers.
Understanding Key Terms
- Thixotropic: Describes a substance that is a gel at rest but becomes fluid when agitated or worked. In this context, the calcium carbonate mix will be thick when left alone but will become easier to spread and manipulate as you work it with a palette knife.
- Campitura: An Italian term referring to the prepared, colored ground layer of a painting. Unlike a simple white gesso, a campitura provides a toned base that can influence the overall warmth, coolness, or luminosity of the subsequent paint layers, often visible through thin paint applications.
