Glazing/Scumbling is a core technique in oil painting that achieves transparent color superimposition, light and shadow transition, or atmosphere creation through a thin layer of pigment. Its essence lies in the interaction between the transparency of the pigment and the reflected light from the base layer. The following is an analysis from the aspects of technique principles, key operation points, material selection and common problems:
First, the core principle of the thin coating technique
The principle of transparent superposition
The thin coating covers the base color with semi-transparent or transparent pigments (such as ultramarine, alizarin red, or light brown), and the base color penetrates through the upper pigment, creating a color blending effect. For example:
Apply cobalt blue as the bottom layer and a thin layer of transparent orange on the top layer, which can present a deep blue-purple color.
Multiple thin applications can enhance color saturation, but the number of layers needs to be controlled to avoid the picture turning gray.
The difference between optical mixing and physical mixing
Physical mixing: Pigments are directly mixed on the palette (such as red + yellow = orange), resulting in a monotonous color and a lack of layers.
Optical blending: By superimposing multiple layers of transparent colors and using human visual blending (such as red layer + yellow layer = visual orange), the colors become richer and more transparent.
Second, key points and steps of operation
1. Underlying processing
Base color selection:
Light-colored bases (such as titanium dioxide base) are suitable for presenting bright scenes and enhancing color reflection.
Dark backgrounds (such as dark brown and ultramarine) are suitable for depicting night scenes or shadows, reducing the amount of paint used.
The dryness of the base color: The base layer must be completely dry (at least 24 hours) to prevent the new coating from mixing with the base pigment.
2. Pigment blending
Dilution ratio:
The ratio of pigment to coloring oil (such as flaxseed oil) is approximately 1:3 to 1:5, creating a fluidity similar to watercolor.
To avoid excessive dilution causing the pigment to flow, the fluidity can be observed on the waste cloth through testing.
Medium selection:
Tinting oil: Enhances gloss and fluidity, suitable for traditional thin application.
Liquin and other quick-drying media: Accelerate drying, suitable for multi-layer stacking.
Resin medium: Enhances transparency and hardness, but long-term durability should be noted.
3. Painting techniques
Tool selection:
Soft-bristled flat-tipped pen: Suitable for uniform application over large areas.
Sector pen: Suitable for edge transitions or creating textures.
Cotton swabs or sponges: used for local shading or softening brushstrokes.
Painting direction:
Apply in one direction (such as from left to right) to avoid overlapping brushstrokes that may cause mottling.
Cross-application should be carried out after the first layer is completely dry to prevent the color from becoming cloudy.
Thickness control
The thickness of each layer should not exceed 0.1 millimeters to avoid covering the details of the bottom layer.
Gradually enhance the color depth through multiple thin applications (3 to 5 layers).
4. Drying and waiting
Drying time:
Each thin coat needs to be dried for 12 to 24 hours (depending on the environmental humidity and the medium).
When drying quickly, a hair dryer (low temperature setting) can be used to accelerate the surface drying, but it is necessary to keep a distance to prevent the pigment from flowing.
Interlayer processing
After drying, the surface can be gently ground with fine sandpaper (400 mesh or above) to enhance the adhesion of the next layer.
After removing the floating dust, apply a new layer to avoid impurities from mixing in.
Third, material selection and precautions
1. Pigment properties
Transparent pigments: Give priority to choosing pigments marked “Transparent” (such as alizarin red, phthalocyanine blue), and avoid using opaque pigments (such as titanium dioxide, zinc white) to cover the base layer.
Semi-transparent pigments: such as raw brown and earthy yellow, can be used in small amounts to add a sense of layering.
Test method: Apply a thick layer of pigment on white cardstock and observe its light transmittance after it dries.
2. Substrate compatibility
Linen: Moderate oil absorption, suitable for traditional thin application.
Oil painting paper: The surface is smooth and a primer needs to be applied in advance to prevent oil absorption from being too fast.
Wooden board: It is necessary to apply base materials (such as rabbit skin glue + chalk) multiple times to form an isolation layer.
3. Common Problems and Solutions
Gray phenomenon:
Reason: The base layer is not completely dry, the pigment is not transparent or there are too many superimposed layers.
Solution: Ensure the base layer is dry, reduce the use of opaque pigments, and keep the number of layers within 5.
Flowing and Dripping
Reason: The pigment is too thin or applied too thickly.
Solution: Adjust the dilution ratio and use multiple thin applications instead of a single thick application.
Poor adhesion
Reason: The bottom layer is not completely dry or there is an excessive amount of medium.
Solution: Extend the drying time and reduce the amount of medium used.
Fourth, the application scenarios of thin coating techniques
Character skin color
The bottom layer is coated with flesh color (such as titanium white + ochre + vermilion), and the top layer is thinly coated with transparent orange and alizarin red to show the blood color and light and shadow.
Scenery and sky
The bottom layer is painted cobalt blue, and the upper layer is thinly painted ultramarine and white to show a gradient cloud layer.
Still life highlights
The base layer is coated with the inherent color of the object, and the upper layer is thinly coated with titanium dioxide to locally brighten the reflective areas.
Fifth, advanced skills
Partial shading: On completed paintings, partially cover with transparent colors (such as shading leaves with transparent green) to enhance the unity of colors.
Scraper assistance: Use a scraper to scrape off part of the thin coating to expose the underlying color and create a mottled effect.
Hybrid technique: Combining thick coating (Impasto) and thin coating, use thick coating in key areas (such as the edges of petals) to highlight the texture, and use thin coating in the background to create an atmosphere.
Summary
The core of the thin coating technique lies in achieving the richness of colors and the layering of light and shadow through the superposition of transparent layers. Its operation must strictly follow the cycle process of “base layer drying – thin pigment – unidirectional brushing – full drying”, and pay attention to the transparency of the pigment, the selection of the medium and the interlayer treatment. Whether it is depicting the delicate texture of the skin or the deep night sky, the thin coating technique can endow oil paintings with a unique transparency and poetic quality.