Which artistic technique involves the gradual blending of colors and tones?

The technique that involves the gradual blending of colors and tones is sfumato. This approach creates a soft transition between colors and tones, often resulting in a hazy or atmospheric effect. Artists use sfumato to convey depth and volume, making forms appear more lifelike and three-dimensional. This technique is particularly associated with the works of Leonardo da Vinci, who masterfully employed it in paintings such as the "Mona Lisa," where the edges of objects and features are seamlessly blended without harsh lines.

Chiaroscuro, in contrast, focuses on the strong contrasts between light and shadow to create a sense of volume and shape in a work of art. Fresco is a mural painting technique involving water-based pigments applied to freshly laid wet plaster. Tenebrismo emphasizes dramatic contrasts between light and dark, often spotlighting certain figures or areas within a darker background. Each of these techniques serves different artistic purposes, but sfumato specifically highlights the soft gradation of color, which is why it is the correct answer.