PubMed1975
With pencils of any color, the first step certainly involves visual examination to distinguish between the color tints and to study the quality of the stroke itself. In many instances by this step alone, 2 pencils can be distinguished if they are the product of 2 different manufacturers. In other words, the most useful of all tests is the visual examination. In the case of red pencils, infrared luminescence reveals significant information and should be resorted to in those instances where two questioned strokes are extremely similar. Study under ultraviolet radiation may also help to establish similarities or differences which are not readily discernible by visual examination. However, reflected infrared examination and study with dichroic filters have no particular value when dealing with red pencil although chemical spot testing may be of some assistance. In the case of blue pencils, a number of brands absorbs infrared radiation to a different extent and some give off distinctive infrared luminescence, so that these 2 tests can assist in distinguishing between certain similar colors or tints. Also, study through dichroic filters has value. Thus, the combination of these 3 tests can be of some advantage, but in most instances, particularly with dark blues, examination under ultraviolet radiation is not particularly helpful. Chemical spot testing has some limited advantages but generally only in combination with all other tests. In the case of green pencils, the same pattern of testing may be used as with blues. Many of the greens absorb infrared rays and some have bright infrared luminescence. Ultraviolet radiation can cause certain greens to fluoresce in a distinctive way. Thus, with each color studied, differences can be revealed and similarities established. Colored pencils are a distinct group of writing instruments. Within any color classification, there is a variety of shades or tints. Although it is not psosible to determine the make of pencil used in any particular writing, it is possible under many circumstances to distinguish between the work of different makes and grades of red, blue and green pencils, as well as other colors which have not been covered by this paper. While visual examination will separate the many different makes, other tests are described which will further assist in grouping or separating colored writing strokes. For a number of reasons, and particularly because of manufacturing procedures of different companies, not every make of pencil is distinctive, but there has been found to be a definite variety within each color group, and many makes are distinguishable.