Crime Scene Training

Overview of Chemical Tools and Methods for Latent Print Development

Powders

Powders adhere to both water and fatty deposits. These are generally useful

on newer prints only. Choose a powder to contrast with the background. They

are useful on any dry, relatively smooth, non-adhesive surfaces. Use after

laser fluorescence. May be used before ninhydrin and after cyanoacrylate.

Results may vary with skill of technician. “Lift” developed prints by

photography or conventional methods.

Fluorescent Powders

Powders made of fluorescent materials offer advantages to the limitations of

conventional powders. Apply as with conventional powders. “Lifts” can be

made photographically or by conventional means. Fluorescent powders are

especially useful on confused backgrounds. An ultraviolet or forensic light

source is required.

Iodine Fuming

Iodine fumes react with oils and fatty deposits to produce a temporary

yellow-brown reaction product. Iodine is useful on fresh prints on porous

and non-porous, non-metallic surfaces. Developed prints must be fixed or

photographed immediately because reaction will rapidly fade. Use iodine

before ninhydrin and silver nitrate.

DFO

DFO, 1,8 Diazafluoren-9-one, is a fluorescing ninhydrin analog found to

develop up to two and a half more prints than ninhydrin itself. It is useful on

porous surfaces, especially paper. Development may be accelerated through

the application of controlled heat. Use it before ninhydrin. DFO also is useful

to develop weak blood stains. It requires a specialized light source, such as

the BLUEMAXX™.

Ninhydrin

Ninhydrin reacts with amino acids to produce a purple reaction product

called “Rhuemann’s Purple”. It is useful on porous surfaces—especially paper.

Development time is up to 10 days, but may be accelerated through the

application of heat and humidity. Use ninhydrin after iodine and before silver

nitrate. Ninhydrin is not useful on items which have been exposed to water.

Silver Nitrate

Silver nitrate reacts with the chlorides in skin secretions to form silver

chloride, a material which turns gray when exposed to light. Developed prints

must be photographed immediately because the reaction will eventually (and

permanently) fill the background. It is useful on paper, cardboard, plastics and

unvarnished, light-colored woods. Use it after ninhydrin and iodine. It is not

useful on items which have been exposed to water.

Physical Developer

Physical developer is another silver-based developer which reacts to form a

dark gray reaction product. It is useful on paper, cardboard, and unvarnished,

light-colored woods. Use physical developer after ninhydrin and iodine. It is

very successful on items exposed to water.

Cyanoacrylate (Glue Fuming)

Cyanoacrylate fumes react (polymerize) with water and other possible

fingerprint constituents to form a hard, whitish deposit. It is useful on most

non-porous and some porous surfaces. Cyanoacrylate produces excellent

results on styrofoam and plastic bags. Developed prints may be dusted with

powders or treated with fluorescing dyes, such as ardrox and basic yellow to

enhance.

Amido Black

Amido black reacts with the proteins found in blood to form a black reaction

product. Amido black is useful only on blood-contaminated prints. It is highly

sensitive. It is useful on non-porous and some slightly porous surfaces. It

sometimes offers successful development of blood prints on dead human

skin

Adhesive Side Powder

Adhesive side powder attaches itself to plastic print impressions on the

adhesive side of tapes. It produces excellent results on light-colored or

transparent tapes, including duct tape, masking tape, plastic surgical tape,

foam tape, clear and reinforced packing tapes and labels. This process

involves wetting tapes.

Fluorochromes

Prints may be treated with special dyes called fluorochromes which easily

are made to fluoresce and bond with the print deposits. They are useful

with forensic lights such as SIRCHIE’s BLUEMAXX™. DFO is a fluorescing

ninhydrin analog found to develop up to two and a half times more prints

than ninhydrin itself. It is useful on porous surfaces. Development may be

accelerated through the application of controlled heat. A specialized light

source such as  SIRCHIE’s BLUEMAXX™ is required. Basic yellow, ardrox, and

rhodamine are dyes especially useful staining latent prints developed with cyanoacrylate.

Download more information: Latent print Development

 

PrinTips 11—An Overview of Latent Print Development Powders

By: Don Penven, Tech Support

Latent print powders come in five different formulations:

Regular-Oxide, Metallic, Magnetic, Combination and Fluorescent. This article covers the basic theory of each type. Keep in mind that if you are uncertain which powder to use on a particular surface—experiment by placing your print in an area not likely to have been touched by the perpetrator.

 Regular-Oxide Powders

These powders are considered the basic choice by crime scene investigators for use on many of the surfaces encountered at crime scenes. But many practitioners are not aware of some of the limitations. Examples of regular-oxides are: black, white, gray and red. These finely milled powders are highly sensitive toward the moisture or oily content of latent fingerprints. But their use should be limited to just non-porous surfaces such as most painted metals, plastics, waxed surfaces, glass, rubber, leather  and wood (painted and unpainted). They should not be used on highly polished surfaces such as chrome or silver plating or other polished metals. Regular-oxide powders are applied with a brush. A powder color is selected based on how much contrast from the background it affords. Use black powder on light-colored surfaces and white powder on dark colored surfaces. Gray and red powders are often used on either light or dark surfaces.

 Metallic Powders

As the name suggests, these powders are formulated from metallic substances such as aluminum, copper and zinc. They are specifically formulated for use on highly polished surfaces like chrome or silver plating. Using a regular-oxide powder on this type of surface generally results in the moisture residue from latent prints being damaged or destroyed—these ridge structures are simply wiped away. Metallic powders are applied with a brush.

 Magnetic Powders

Magnetic powders are formulated from iron or iron oxide. The powders themselves are not magnetic, but they are easily magnetized by a magnetic wand. Magnetic powders may be used on virtually any surface EXCEPT a surface containing iron or steel. The principle of delivery is this: a magnetic wand is passed over the powder, which is then attracted to the wand to form a “brush” made of the powder. The CSI then passes this powder brush over the surface so that the tip of the wand does not touch the surface, but the powder does.  When carefully applied, magnetic powders leave very little surface residue so cleanup is simplified. Magnetic powders are available in black, gray and white for contrast with the surface.

 Combination Powders

These powders combine the properties and chemistry of both regular-oxide powders and metallic powders. The benefits here are:

1. Combination powders may be used on virtually ANY non-porous surface
2. These powders appear dark on a light background and light on a dark background.

Combination powders are applied with a brush.

 Fluorescent Powders

Note: fluorescent powders use a formulation similar to regular-oxide powders and are thus best suited to work on those surfaces mentioned above.

Fluorescent powders appeared in the crime scene kits of CSIs who wanted a powder that was usable on multi-colored, confused backgrounds like soda cans, snack wrappers and bags, wallpaper, ceramic surfaces, etc. These powders contain a chemical that produces fluorescence when exposed to ultraviolet (UV) light or certain frequencies from alternate light sources (blue, yellow, green and red). When developed latent prints are viewed under subdued ambient light the fluorescence is bright enough that when the prints are photographed, the background is mostly dropped out. Fluorescent powders are applied with a brush.

 For more information on latent print development using powders, chemicals and fuming techniques, download the Latent Print Development section of our catalog and read over pages 9-12.        Latent Print Development

To receive notice when new blog posts are available; Signup For Email Alerts