# Properties of Dyes for Painting with Spectroscopy in the Visible and Near Infrared Range
## 1 Introduction  
Each dye has its own characteristic properties of light absorption and reflection in the visible (V) and near infrared (NIR) spectra. Accordingly, every artistic painting, in addition to the image intended for the naked eye, has its own characteristic NIR image. In flora and fauna, each type of matter has its own characteristic colors with its own properties in relation to light [1]. In nature, we find the same hues with completely different substance compositions [2]. In this article, we use the term \"color\", which is specific to our eyes and refers only to the visible V portion of sunlight, described numerically from 400 to 760 nanometers [3]. The substance that carries the color is called dye, pigment, or colorant. In this article, we extend the study of the properties of dyes from the V spectrum to the NIR spectrum. The first part of the NIR spectrum, ranging up to 1000 nm, is called the \"Z\" region [4]. The \"VZ\" infrared is an abbreviation of \"VIS\" and \"Z region\" (NIR region). Significant differences in light absorption in the NIR spectrum are used in the development of a new type of painting art, and two different images are created on the same paper. Each color tone can be realized in at least two different material compositions, with two different appearances in the NIR spectrum [5]. The uniformity and diversity of the light reflection of the painted material is used by artists to express themselves in their own personal ways [6].  
Artists gain new knowledge about the matter of dyes, as well as a new instrumental view of matter, and discover new processes and tools in the creation of visual art [7].  
In this paper, we present the characterization of a painter's canvas with standard paint colors whose wavelengths were measured before application to the canvas, where the response of each color in the visible and infrared spectra was studied. Targeted measurements were made with the aim of creating a double image, of which the hidden image is visible in the infrared spectrum [8].  
The image in the infrared spectrum can be observed by IR detectors and other types of cameras that read the image at 1000 nanometers. The IR image is embedded in theimage visible to the eyes. Today's museums and galleries are equipped with surveillance and monitoring devices that enable the viewing of images in the infrared spectrum [9]. Research on infrared painting and pigments is focused on the restoration of artworks by old masters, as well as the restoration of contemporary artworks [10].  
It has been shown that painting dyes have been characterized by a duality throughout history, although the old masters were not aware of it. The use of infrared reflectography to reveal \"overpainting\" in artworks is a particularly interesting area of research [11].  
The results of creating and applying two dependent images in two spectral regions have the possibility of widespread application and implementation, excluding fine arts and design. By comparing individual applications and measurements, which we describe in detail in this paper, one can create a basis for new realizations [12]. This method is based on the color property whereby any hue in the visible spectrum can be achieved in an infinite number of ways, while colors can also be defined as situated outside the range of wavelengths perceivable to the human eye, which can become visible to humans through the use of infrared cameras, which we already use for viewing at night.  
In printing practice, dyes for artistic painting are simulated with conventional dyes. Simulation is executed with printing dyes in dual spectra without the usage of additional colors [13] ([PERSON], Principles of Image Printing Technology, pp. 252-261). The equality of two dyes is determined with the \"\(\Delta\)E\" algorithm [14], which covers only the visible V spectrum [3].