Hidden fingerprint design for decades challenged crime scene investigators. Forensic medical examination fingerprints occurred from the early use of lamp fat (soot) to complex formulas that used complex chemistry. This article will discuss the use of latent fingerprint powders included in a form and formulas for hidden powders.
Hidden powders for printing are divided between several different categories — each category has very specific uses. The first consideration for a crime scene investigator that needs to be examined is the type of surface that is expected to give hidden fingerprints:
Porous surfaces : This is paper, cardboard and raw wood. It is assumed that latent prints with Latin letters are considered quite fresh, latent printed powders are not very useful on non-porous surfaces, since the moisture content is dispersed in the details of the substrate and the ridge.
Non-porous surfaces: This is where latent powders appear most often. However, the problem lies in the fact that all non-porous surfaces have different characteristics that require a certain formula of the hidden powder.
Hidden powder formulations: Hidden powders fall into the following categories:
1. Standard oxide powders: this category covers formulations that have been used for nearly a century. Black, white, gray and red are included.
2. Metal powders: These powders are composed using real, finely ground metal particles such as aluminum, copper and bronze.
3. Magnetic powders: all magnetic powders have iron or iron oxide as the main ingredient - a material that easily magnetizes.
4. Fluorescent powders: fluorescent powders have a special use - they are ideal when applied to multi-colored backgrounds. Once it is identical that latencies are present after development, CSI reduces the available light and uses a UV lamp or alternative light sources (blue, green, or red) to obtain fluorescence. These advanced lattes actually “glow” in the dark.
5. Combined powders: a problem that is often encountered in the development of hidden printing is viewing hidden printing on a dark surface when using light powder or vice versa. Another problem is the difference between smooth surfaces and surfaces of highly polished metals, such as silver-coated or chrome-plated surfaces. This powder combines the properties of oxide and metal powder, and one formula can be used on dark or light backgrounds.
As mentioned above, all non-porous surfaces do not resemble each other when it comes to choosing a latent printing powder. For example: automotive standard oxide powders can be used on painted surfaces, but metal powder should be used on chrome-plated areas such as bumpers and trim.
Magnetic powders were invented in the early 1970s, and they occupy a prominent place in the set of crimes. Magnetic powders can be used on almost any surface. EXCLUDE surfaces that contain iron or steel. All other powders are applied using a brush - animal (camel or protein) or synthetic materials, such as fiberglass or carbon fiber. Pen vacuum cleaners are also mainly used as a cleaning tool after a regular brush is used to design a print. Feathery pollen will remove excess powder in case of development. Magnetic forces are applied with a magnetic stick, and magnetic powders stick to the magnet, actually forming a “brush” that touches the surface, not the bristles of the brush.
Fluorescent powders are also available for several decades. They all contain a pigment that emits light other than white. This fluorescence is especially useful on multi-color backgrounds, such as temperature jars, potato chips and candy wrappers. In low light conditions, these powders become fluorescent when exposed to long-wave UV radiation (black light). Many fluorescent powders are also visible under alternative light sources, but fluorescence is not visible, since the light from the source suppresses the faint fluorescence. To compensate for this, the crime scene investigator uses a filter - depending on the color of the alternative light source (ALS) - which is mostly blue, green or red. An orange or yellow filter blocks blue and green visible light, and a red red filter is used for red ALS.
