Among the color material, those used for the purpose of making pictures are called "paints". A "paint" is a mixture of a colorant (pigment) and a vehicle, and the colorant should not be soluble in the vehicle. Even in the long history of painting, the essence of these paints has not changed. Production of paintings is entrusted to the technique of the painter individual, and in the world of sensitivity, unique matières are created. Although the paint has been improved by using various assistants, it is believed that maximizing the performance of the pigment leads to better paint making. An oil paint "YUICHI" was presented as a result of cooperative research with the oil painting technique materials laboratory of Tokyo art university.

"YUICHI" is a primitive oil paint of the age when it was kneaded only with pigment and oil, and was completed as a modern oil paint based on the painter's sensibility by introducing modern high-performance production technology.

Techniques of expression by oil painting are related to the property of oil paint. Especially, there are drying oil, petrol, etc. By means of high transparency and high plasticity, Glazing Techniques and Alla Prima exist. Oil painting will develop because of expression by mixed technique in the future.

A scientific investigation on oil paintings is carried out nondestructively and noncontactly for conservation, elucidation of painting techniques and restoration of oil paintings. Photographic techniques such as infrared photograph, fluorograph, X-ray photograph, oblique lighting photograph and microphotograph, and also spectrometric techniques such as X-ray and reflection spectrum, are applied to the scientific investigation on oil paintings. Photograph techniques are done to observe the conditions and internal structures of oil paintings, also spectrometric techniques are performed to analyze the compositions and distributions of oil paints. These techniques of the scientific investigation have been established relatively early and are in practical use. Recently, novel scientific analysis methods and data analysis methods have been studied and developed. This paper describes the conventional and novel techniques reported for the scientific investigation.