RU2794978C2 - Method for producing magnetic dactyloscopic powder based on highly dispersed powders for detection of latent hand traces - Google Patents

Abstract

FIELD: forensic science and criminalistics.

SUBSTANCE: invention is related in particular to detection of invisible or barely visible fingerprints left on various trace-bearing surfaces, when identifying a person. Mechanical mixing of the particles of the mixture components with a solvent containing a mixture of surfactants is carried out, drying, grinding and sifting the resulting mixture through a sieve. The powder contains, in % of weight: iron 20-50, iron oxide 20-50, soot 10-40, talc 1-15, sorbitan stearate 1-5, polyethylene glycol ether of FFA monoethanolamide 1-5.

EFFECT: invention improves selectivity of adhesive properties of the developed magnetic fingerprint powder in relation to the surface of the papillary line of the sweat-fat trace due to the optimally selected surface properties of the highly dispersed medium, which makes it possible to detect sweat-fat traces of a person on a wide range of trace-bearing surfaces, in particular on metal, polymer, ceramic, glass, paper, while achieving a high contrast of detected dry and old traces.

1 cl, 1 tbl

Description

The invention relates to the fields of forensic science, forensic science and the chemical industry, in particular to the field of diagnosing a person's identity, namely, to identifying invisible or barely visible fingerprints left on various trace-receiving surfaces, when identifying a person's identity.

Known black magnetic fingerprint powder [1] with the following ratio, wt.%:

powdered iron 5.5-75 Manganese-zinc ferrite 20-82 Talc 0.5-15

Among the disadvantages of using these powder compositions is the low detecting ability of traces, namely, the details of the papillary pattern are not sufficiently distinguishable, there is a high veil and low contrast.

The disadvantages of this composition also include the variability of the granulometric and component composition of manganese-zinc ferrite, which is a by-product of metallurgical processes, which will lead to significant changes in the revealing ability of the fingerprint powder.

Known coloring dactyloscopic powder [2], which consists in mixing two components, and iron powder with dimensional characteristics of 1-3 microns is used as a carrier, and ultrafine iron powder obtained by means of an electric explosion in an inert medium is used as a coloring agent.

The disadvantages of using these powders are the high adsorption capacity for trace-receiving surfaces, the low clarity of the details of the papillary pattern, and the use of expensive equipment.

Known black fingerprint powders [3] with the following ratios of components, wt.%:

1) iron oxide (III) - 50, rosin - 25, soot - 25;

2) manganese oxide - 45, iron (III) oxide - 25, soot - 25, rosin - 5.

The disadvantages of using these powders is poor-quality detection of traces, which manifests itself in low selectivity with respect to trace-receiving surfaces and, as a result, leads to “clogging” of the hand trace, there is a low clarity of the details of the papillary pattern.

A known method of obtaining colored fingerprint magnetic powders based on the natural mineral magnetite [4]. Magnetite powder with a maximum particle size of not more than 100 µm is mixed with a solution of stearic acid in acetone and mixed thoroughly. The resulting mass is dried at a temperature not exceeding 60°C and the dried product is ground in a mortar to crush lumps, after which the powder is ready for use.

The disadvantage of this method is its multi-operation, complexity due to the use of additional reagents and insufficiently high clarity in identifying traces in fingerprinting.

Closest to the invention in terms of technical essence is as a prototype a method for obtaining stained fingerprint magnetic powders [5] by grinding and mixing ferrites or metallic iron with a solvent containing a surfactant, for example, stearic acid with a concentration of 0.01 mol/l in an amount 4% (mass.).

The disadvantages of this powder is a high "veil", a low ability to detect human sweat marks on such common surfaces as plastic surfaces, glass, ceramic, which leads to a "blurring" of the trace, resulting in low clarity of papillary pattern details.

The invention is based on the task of developing a method for obtaining a magnetic fingerprint powder based on a mixture of fine iron powders, iron oxides, modified with mixtures of surfactants to detect latent handprints, devoid of the above disadvantages. The technical result that can be obtained by implementing the invention: the selectivity of the adhesive properties of the magnetic fingerprint powder being developed in relation to the surface of the papillary line of the sweat mark due to the optimally selected surface properties of the finely dispersed medium, which makes it possible to detect sweat marks of a person on a wide range of trace-bearing surfaces, in particular, such as metal, polymer, ceramic, glass, paper and others. A high contrast of detected dry and old traces is also achieved.

This technical result is achieved by the fact that a method is proposed for obtaining a magnetic fingerprint powder based on highly dispersed powders of iron, iron oxides, modified with mixtures of surfactants to detect latent handprints, including iron, iron oxide, soot, talc, a mixture of surfactants.

The objective of the invention is to create such a magnetic fingerprint powder that would have better trace-detecting properties than known powders, with a simplified technology for its manufacture, that is, expanding the arsenal of fingerprint powders.

This task is achieved by the fact that the claimed magnetic fingerprint powder based on fine powders of iron, iron oxides, modified with mixtures of surfactants, contains iron, iron oxide, carbon black, talc, a mixture of surfactants, for example, sorbitan stearate and polyethylene glycol ether of monoethanolamide FFA at the following ratio of components, wt.%:

Iron 20-50 iron oxide 20-50 Soot 10-40 Talc 1-15 Sorbitan stearate 1-5 Polyethylene glycol ether monoethanolamide FFA 1-5.

To achieve this task, samples of magnetic fingerprint powder for testing are obtained by mechanical mixing of particles of mixture components with a solvent (for example, alcohol or acetone) containing a mixture of surfactants. The mixture is dried at a temperature not exceeding 70°C. The resulting mass is crushed and sifted through a sieve. Paper, foil, polymer film, glass, painted wooden surface, and ceramics are used as trace-receiving surfaces with handprints. Colorless sweat-fat traces of hands with different storage periods (from one day to several months) are used, which are left by a person with obviously high-quality papillary lines (papillary patterns are not “erased”, papillary lines are of sufficient thickness, pores are clearly visible) and with a sufficient amount of sweat-fat substance. Traces are packed in paper envelopes and stored at normal humidity and room temperature. After a certain period of time, the object with traces is treated with magnetic fingerprint powder using a magnetic fingerprint brush. The optimal ratio between the components of the mixture was established experimentally.

A positive result is an identified trace, in which the papillary pattern is clearly visible, there is no veil and there is no adhesion of powder particles in the region of the interpapillary space of the trace on the trace-perceiving object. In the event that on at least one of the trace-receiving surfaces the quality of trace detection does not satisfy the above conditions, the result is considered negative.

Table 1 shows the results of testing magnetic fingerprint powders of various compositions.

When using powders No. 1-5, papillary patterns are characterized by high clarity and contrast. In the identified traces, the details of the papillary pattern are clearly distinguishable, which makes it possible to recognize them as sufficient for identifying a person during a forensic examination. Thus, the combination of these components at their quantitative ratio makes it possible to obtain compositions of a magnetic fingerprint powder with the properties required for practical use.

The traces identified by the powders "Prototype" and No. 6-7 are heterogeneous, low contrast and, due to the high adsorption capacity for trace-receiving surfaces, are unsuitable for identification.

Thus, obtaining a magnetic fingerprint powder based on highly dispersed iron powders, iron oxides, modified with mixtures of surfactants to detect latent handprints with improved adhesive properties due to increased adhesion of the components of the fingerprint powder to the sweat-fat substance of the trace and trace and to the trace-receiving surfaces when detecting invisible and faintly visible traces can be used in the field of forensics.

Information sources

1. Patent No. 11714 C1 2009.04.30. Republic of Belarus. Black magnetic fingerprint powder. Authors: Vorobieva S.A., Lesnikovich A.I., Milevich I.A.; Semenova E.M.

2. RF patent No. 2080822 C1 06.10.1994. Method for producing coloring fingerprint magnetic powders. Authors: Ilyin A.P., Vokhmintsev B.K., Krasnyatov Yu.A., Kunitsyn A.A.

3. Advances in Fingerprint Technology /edited by Henry C. Lee, Robert Ramotowski, R.E. Gaensslen, p. 120, 2001

4.A.C. USSR No. 1473118 class. A C61B 5/10, 1986.

5.A.C. USSR No. 542949 class. C01N 27/28, 1977 Method for producing magnetic powders (prototype).

Claims (2)

A method for producing a magnetic fingerprint powder based on finely dispersed powders for detecting latent handprints, including mechanical mixing of particles of the mixture components with a solvent containing a mixture of surfactants, drying, grinding and sifting the resulting mixture through a sieve, characterized in that as a mixture of surface-active active substances use sorbitan stearate and polyethylene glycol ether of FFA monoethanolamide, while the powder contains components in the following ratios, wt.%: Iron 20-50 iron oxide 20-50 Soot 10-40 Talc 1-15 Sorbitan stearate 1-5 Polyethylene glycol ether monoethanolamide FFA 1-5