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Visualization Method | Use | Limitations |
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Amino Black | Protein dye is sensitive to blood, turning a blue-black color in its presence. Treatment with a physical developer may be done after amido black to improve the developed print. | It will not stain the normal constituents in a latent print. Amido black should not be used as a presumptive test for blood because it reacts to more than only blood. |
Aqueous amido black | The protein dye solution is sensitive to blood, turning a blue-black color in its presence. Treatment with a physical developer may be done after amido black to improve the developed print. Can be washed over any nonporous surface; the item may also be submerged in the solution. | It will not stain the normal constituents in a latent print. Amido black should not be used as a presumptive test for blood because it reacts to more than only blood. May permanently stain some surfaces. Presumptive blood tests should be done before using aqueous amido black. It is corrosive and will damage metal surfaces if not washed off quickly. |
Aqueous leucocrystal violet | Enhances and develops latent prints stained with blood on porous or nonporous surfaces. Best applied by washing or submersion. | It will not stain the normal constituents in a latent print. May permanently stain some surfaces. |
Gentian crystal violet | A protein-dye that stains the fatty portions of sebaceous sweat a deep purple color; it also works on bloody prints. GCV will visualize latent prints on the adhesive side of all tapes. Fluoresces at 525, 530, and 570nm (use red goggles); also at 485 and 450nm (use orange goggles). | May permanently stain some surfaces. |
DFO (1,8-Diazafluoren9-one) | A ninhydrin analog that reacts to the amino acids present in body proteins; is especially good for paper evidence. | Not recommended for spraying. Special conditions apply to photography. |
Glue fuming | Fumes from cyanoacrylate ester adhesives will develop latent prints by binding the proteins in the prints. The cyanoacrylate ester adhesive is heated in the presence of water to create the fumes. | The fumes from cyanoacrylate ester adhesives are irritating but nontoxic. |
Iodine | Fumes from iodine crystals develop latent prints on surfaces that are impractical for traditional dusting or have residues such as grease. The FBI has developed a method for spraying iodine solutions on large surfaces, such as walls. | Latent prints developed with iodine are visible for only a few hours. |
Ninhydrin | Develops latent prints on porous surfaces like paper by reacting with amino acids in latent print residue. In a fume hood, the specimens are submerged in the ninhydrin solution and then air-dried. | Avoid contact with the powder and solution form of ninhydrin. Any source of heat or spark should be avoided. |
Physical developer | A silver-based liquid reagent that reacts to lipids, fats, oils, and waxes present in the print residue. It is good for porous objects but should be the last process in the chemical sequence. | Numerous safety precautions are required for physical developers. Paper with a pH above 7 (like thermal fax paper) is not suitable for processing with a physical developer |
Small particle reagent (Molybdenum disulfide, MoS2) | A physical development technique in which small black particles adhere to the fatty substances left in print residue and is useful on many different surfaces. | Numerous safety precautions are required for small particle reagents. Developed prints should be photographed before lifting is attempted. |
Sudan black | Working best on glass, metal, or plastic materials that are greasy or sticky, Sudan black is a dye that stains the fatty components of sebaceous secretions. Sudan black also works well on the inside of latex gloves. | Stains many surfaces. Should not be used on porous or absorbent surfaces. |
Vacuum metal deposition | This is reported to be the most effective technique for most smooth, nonporous surfaces. The process evaporates gold or zinc in a vacuum chamber that coats the specimen surface with a microscopic layer of metal. | The equipment is expensive. |
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Three Main Types of Lasers are used to detect fingerprints:
Loops – have one or more ridges entering from one side of the print, curving back on themselves, and exiting the fingertip on the same side.
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The modern system of fingerprint classification is based on Henry’s original design, which could process a maximum of 100,000 sets of prints, with modifications by the FBI to allow for the huge number of entries that have accumulated over the years.
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Right thumb, right index | 16 |
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Right middle, right ring | 8 |
Right little, left thumb | 4 |
Left index, left middle | 2 |
Left ring, left little | 1 |
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All arches are considered “nonnumerical” patterns and are given a value of zero. Whorls are given values depending on which finger they appear.
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Level 1 detail
Level 2 detail
Level 3 detail
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