Tracing paper is paper made to have low opacity, allowing light to pass through. It was originally developed for architects and design engineers to create drawings that could be copied precisely using the diazo copy process; it then found many other uses. The original use for drawing and tracing was largely superseded by technologies that do not require diazo copying or manual copying (by tracing) of drawings. The transparency of tracing paper is achieved by careful selection of the raw materials and the process used to create transparency. Cellulose fibre forms the basis of the paper, usually from wood species but also from cotton fibre. Often, paper contains other filler materials to enhance opacity and print quality. For tracing or translucent paper, it is necessary to remove any material which obstructs the transmission of light. Description Tracing paper is paper made to have low opacity, allowing light to pass through. It is named as such for its ability for an image to be traced onto it. It was originally developed for architects and design engineers to create drawings which could be copied precisely using the diazo copy process. When tracing paper is placed onto a picture, the picture is easily visible through the paper. Thus, it becomes easy to find edges in the picture and trace the image onto the tracing paper. Pure cellulose fiber is translucent, and it is the air trapped between fibers that makes paper opaque and look white. If the fibers are refined and beaten until all the air is taken out, then the resulting sheet will be translucent. Translucent papers are dense and contain up to 10% moisture at 50% humidity. Production Tracing paper is usually made from sulfite pulp by reducing the fibres to a state of fine subdivision and hydrolysing them by very prolonged beating in water. There are three main processes to manufacture this type of paper, as follows: Through mechanical ‘refining’ of the cellulose fibre to create a fibre which is highly fibrillated and gelatinous, so that in forming the sheet of paper, virtually all air is excluded from the internal structure of the paper. This method produces a very translucent and even looking paper over a range of areal densities from 42 to over 280 g/m2. By making a ‘normal’ sheet of paper and then filling the spaces between the fibres with a material that has the same refractive index