ABSTRACT
This chapter concentrates on writing materials such as inks and paper. Many of the techniques employed to distinguish between paper or inks involve the use of light, or, to be more precise, electromagnetic radiation, so it is helpful to have a basic understanding of this. Light is essentially electromagnetic radiation of certain wavelengths or frequencies that can be detected by the eye, and different people will be able to see a slightly different range of light. Sources of light are rarely monochromatic—that is, of one wavelength. Sunlight or the radiation from a conventional electric light bulb contain wavelengths in the whole range, and their combined effect on the eye causes it to see a white light. Filtered light techniques are a convenient way of distinguishing between materials and suffice in most cases encountered by document examiners. Luminescence can also be tested without change to the paper.
