GOV.UK
`
`1. Home (https://www.gov.uk/)
`
`Guidance
`
`Fingerprint Source Book: manual of development
`techniques
`
`From:
`Part of:
`
`Home Office (https://www.gov.uk/government/organisations/home-office)
`Centre for Applied Science and Technology (https://www.gov.uk/government/collections/centre-for-
`applied-science-and-technology-information)
`Published:
`26 March 2013
`A manual drawing together all of the information regarding experimental work on fingerprint
`development techniques.
`
`Documents
`
`Chapter 1 Fingerprint Source Book: introduction
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143860/fsb-
`chap1-introduction.pdf)
`
`PDF, 229KB, 9 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 2 Fingerprint Source Book: finger mark examination techniques within
`scope of ISO 17025
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143861/fsb-
`chap2-examination.pdf)
`
`PDF, 953KB, 36 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Reactive Surfaces Ltd. LLP
`Ex. 1044 (Ray Attachment J)
`Reactive Surfaces Ltd. LLP v. Toyota Motor Corp.
`IPR2016-01914
`
`

`

`Chapter 3 Fingerprint Source Book: finger mark development techniques within
`scope of ISO 17025, sections 1 to 3
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143862/fsb-
`chap3-sec1to3-development.pdf)
`
`PDF, 3.38MB, 66 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 3 Fingerprint Source Book: finger mark development techniques within
`scope of ISO 17025, sections 4 to 6
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143863/fsb-
`chap3-sec4to6-development.pdf)
`
`PDF, 3.56MB, 73 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 3 Fingerprint Source Book: finger mark development techniques within
`scope of ISO 17025, sections 7 to 9
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143864/fsb-
`chap3-sec7to9-development.pdf)
`
`PDF, 3.81MB, 55 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 3 Fingerprint Source Book: finger mark development techniques within
`scope of ISO 17025, sections 10 and 11
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143865/fsb-
`chap3-sec10and11-development.pdf)
`
`

`

`PDF, 3.96MB, 57 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 4 Fingerprint Source Book: finger mark imaging techniques
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143866/fsb-
`chap4-imaging.pdf)
`
`PDF, 3.35MB, 33 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 5 Fingerprint Source Book: alternative finger mark development
`techniques
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143867/fsb-
`chap5-alt-development.pdf)
`
`PDF, 4.23MB, 162 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`Chapter 6 Fingerprint Source Book: specialist imaging techniques
`(https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/143868/fsb-
`chap6-spec-imaging.pdf)
`
`PDF, 2.43MB, 20 pages
`
`This file may not be suitable for users of assistive technology.
`
`If you use assistive technology (such as a screen reader) and need a version of this document in a more
`accessible format, please email alternativeformats@homeoffice.gsi.gov.uk. Please tell us what format you need. It
`will help us if you say what assistive technology you use.
`
`

`

`Details
`
`The Fingerprint Source Book was prepared as an internal reference document, drawing together all of the
`information held by the Home Office Centre for Applied Science and Technology (CAST) regarding internally
`managed experimental work on finger mark enhancement techniques. The preparation of the document was
`carried out in anticipation that supporting evidence would be required for validation of the techniques within the
`Manual of Fingerprint Development Techniques, as part of the ISO 17025 accreditation of the CAST forensic
`laboratories.
`
`As CAST and police force laboratories have progressed with the ISO 17025 accreditation process, the Fingerprint
`Source Book has become regarded as a more widely important document. Because it provides the validation of
`the techniques contained within the manual, and hence the techniques used by police forces, it has become
`necessary for the document to be formally issued and controlled.
`
`Published: 26 March 2013
`
`From: Home Office (https://www.gov.uk/government/organisations/home-office)
`
`Part of: Centre for Applied Science and Technology (https://www.gov.uk/government/collections/centre-for-applied-
`science-and-technology-information)
`
`

`

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`Fingerprint Source Book
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` S
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` M Bleay
`V G Sears
`H L Bandey
`A P Gibson
`V J Bowman
`R Downham
`L Fitzgerald
`T Ciuksza
`J Ramadani
`C Selway
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`Fingerprint Source Book - Authorisation
`
`Authorisation
`
`This Fingerprint Source Book has been signed off to my satisfaction and is
`authorised for circulation, as appropriate.
`
`CAST recognises that the information contained within it, while believed to be
`correct at the time of writing, may be subject to change as more information
`becomes available. We would welcome feedback from those using the book,
`which will be subject to regular review to incorporate appropriate changes.
`
`
`
`
`Steve Barber
`Chief Technical Officer (Home Office CAST) ..…………………………………………
`
`
`Signature ………………………………..
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`
`
`12 March 2012
`Date …………………………
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`This Page Intentionally Left Blank
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`- ii -
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`Fingerprint Source Book - Preface
`
`Preface
`
`This preface places the publication of this Fingerprint Source Book into
`context, and represents the situation at the time of writing (October 2011).
`
`The Fingerprint Source Book was not originally intended as an external
`publication. It was prepared as an internal reference document, drawing
`together all of the information held by the Home Office Centre for Applied
`Science and Technology (CAST) regarding internally managed experimental
`work on finger mark enhancement techniques. The preparation of the
`document was carried out in anticipation that supporting evidence would be
`required for validation of the techniques within the Manual of Fingerprint
`Development Techniques, as part of the ISO 17025 accreditation of the CAST
`forensic laboratories. The original purpose of the document was to
`demonstrate to UKAS (the ISO 17025 assessors) and the Forensic Science
`Regulator that the processes and sequences outlined in the manual had been
`experimentally tested and that the advice presented in the manual was valid.
`
`As CAST and police force laboratories have progressed with the ISO 17025
`accreditation process, the Fingerprint Source Book has become regarded as
`a more widely important document. Because it provides the validation of the
`techniques contained within the manual, and hence the techniques used by
`police forces, it has become necessary for the document to be formally issued
`and controlled. This means that the data contained within it can be directly
`referred to by individual police forces seeking ISO 17025 accreditation, thus
`reducing the requirement on police forces to conduct lengthy validation
`experiments of their own (although local verification experiments will still be
`required). The Forensic Science Regulator has also requested that the data
`contained within the Fingerprint Source Book is made publicly available for
`reasons of transparency.
`
`The document is now presented for use as a controlled document. It is not
`produced as a formal, numbered Home Office document because this is
`incompatible with the contents. However, the document has been reviewed by
`the Home Office communications team to ensure that fundamental formatting
`is acceptable, and a technical review has been carried out covering both
`internal and external peer reviews of the contents.
`
` user of the Fingerprint Source Book should be aware of the original purpose
`for which it was prepared. Although it may be a useful source of data for those
`wishing to conduct research or learn more about various enhancement
`processes, it is not intended to be a text book. It has been prepared for
`laboratories that are currently working to the Home Office CAST Manual of
`Fingerprint Development Techniques, therefore the principal formulations
`described in the source book are those recommended by CAST in the
`manual. Less attention is given to formulations produced by other
`organisations, and to processes that are not included in the manual.
`Significant numbers of the references may refer to reports produced by
`students working at CAST rather than external journal publications. The user
`
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`v1.0
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`Fingerprint Source Book - Preface
`
`must therefore be aware that it will not always be possible to obtain copies of
`every document referred to in the text.
`
`Most sections in the Fingerprint Source Book were last extensively reviewed
`in mid-2010. There have been developments in several areas since then, and
`CAST has also conducted additional research. It must therefore be
`recognised that the information contained within this document may not be
`fully up to date, although a review schedule has been put in place for ongoing
`maintenance of the document.
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`- iv -
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`v1.0
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`Fingerprint Source Book – Table of contents
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`i
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`Table of contents
`
`Authorisation
`
`
`Preface
`
`1. Introduction
`
`2. Finger mark examination techniques within scope of ISO17025
`
`2.1 Visual examination
`
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`2.2 Fluorescence examination
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`39
`3. Finger mark development techniques within scope of ISO17025
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`39
`3.1 Acid dyes (acid black 1, acid violet 17, acid yellow 7)
`
`62
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`3.2 Basic violet 3 (Gentian Violet)
`
`
`
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`82
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`3.3 1,8-Diazafluoren-9-one (DFO)
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`3.4 Ninhydrin
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` 105
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`3.5 Physical developer
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` 135
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`3.6 Powders
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` 157
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`3.7 Powder suspensions
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` 178
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`3.8 Small particle reagent
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` 206
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`3.9 Solvent black 3 (Sudan Black)
`
`
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` 219
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`3.10 Superglue (cyanoacrylate fuming)
`
`
` 233
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`3.11 Vacuum metal deposition
`
`
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` 269
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`4. Finger mark imaging techniques
`
`4.1 Ultraviolet imaging
`
`
`4.2 Infrared imaging
`
`
`4.3 Multispectral imaging
`
`
`
` 322
`
`5. Alternative finger mark development techniques
`
` 322
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`5.1 Alternative blood reagents
`
`
`
` 338
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`5.2 4-Dimethylaminocinnamaldehyde (DMAC)
`
` 347
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`5.3 Electrochemical techniques
`
`
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` 347
`5.3.1 Etching and electrodeposition
`
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` 351
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`5.3.2 Heating and electrostatic powdering
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` 354
`5.4 Electrostatic detection apparatus (ESDA)
`
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` 361
`5.5 Fuming techniques
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` 365
`5.6 Gelatine lifting
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`5.7 1,2 Indandione
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` 392
`5.8 Ninhydrin analogues
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`5.9 Miscellaneous amino acid reagents
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` 398
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` 398
`5.9.1 Fluorescamine
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` 402
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`5.9.2 O-phthaldialdehyde
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` 407
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`5.9.3 Genipin and lawsone
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` 414
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`5.9.4 Alloxan
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`5.9.5 4-chloro-7-nitrobenzofurazan (NBD chloride)
` 416
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`5.9.6 Dansyl chloride
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` 418
`5.10 Iodine
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`5.11 Multimetal deposition
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`Fingerprint Source Book – Table of contents
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`5.12 Oil Red O
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`5.13 Other lipid specific reagents
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`5.13.1 Ruthenium tetroxide (RTX)
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`5.13.2 Osmium tetroxide
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`5.13.3 Europium chelate
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`5.14 Radioactive sulphur dioxide
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`5.15 Silver nitrate
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`6. Specialist imaging techniques
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`6.1 Scanning electron microscopy
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`6.2 X-ray imaging
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`6.3 Other specialist imaging techniques
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`6.3.1 Secondary ion mass spectrometry (SIMS)
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`6.3.2 Scanning Kelvin probe
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`Fingerprint Source Book – Chapter 1: Introduction
`
`Chapter 1: Introduction
`
`The Fingerprint Source Book is primarily intended to provide the background
`and validation for the techniques currently (up to 2011) recommended by the
`Home Office Scientific Development Branch (HOSDB), now the Centre for
`Applied Science and Technology (CAST), and to publish, in some cases for
`the first time, data collected over 35 years of research. It will therefore often
`present information in an ‘CAST-centric’ way, emphasising research that was
`carried out at Sandridge or Horseferry House, possibly sometimes at the
`expense of research carried out elsewhere. It is not the intention of the
`authors to ignore the significant contributions made by other research groups
`and apologies are made in advance if this sometimes appears to be the case.
`The document is also aimed at providing the UK Forensic Science Regulator
`and the United Kingdom Accreditation Service (UKAS), which will carry out
`ISO 17025 accreditation in the UK, with the background evidence behind the
`advice given in the Manual of Fingerprint Development Techniques.
`
`The priorities of CAST in issuing and supporting the Manual of Fingerprint
`Development Techniques and the Fingerprint Development Handbook are to
`provide techniques that are highly effective, safe to use, and can be applied
`by staff who are not necessarily highly-qualified scientists. When developing
`formulations the approach is to maintain the effectiveness of the technique
`while minimising or eliminating any components that have health and safety
`issues associated with them. In some cases, more effective formulations or
`processes may be available, but if they are not felt to be safe to use they will
`not be recommended.
`
`It should be emphasised that all testing and optimisation of processes by
`CAST has been carried out under UK climatic conditions. It is recognised that
`in many parts of the world the conditions of temperature and humidity will
`differ significantly from those in the UK and in some cases this may affect
`performance. It is likely that optimised formulations in different countries may
`differ for this very reason.
`
`Throughout the report, references are made to the two main fingerprint
`research groups in the UK, CAST and the Forensic Science Service (FSS).
`These organisations have changed names several times in the 35 years
`covered, and in the text reference is usually made to the name of the group at
`that time. However, inconsistencies may arise. In summary, previous names
`for each organisation have been:
`
`CAST
`
`Police Research and Development Branch (PRDB) 1969 -1971
`Police Scientific Development Branch (PSDB) 1971 - 1981
`Home Office Scientific Research and Development Branch (HO SRDB) 1981 -
`1991
`Police Scientific Development Branch (PSDB) 1994 -2004
`Home Office Scientific Development Branch (HOSDB) 2004 - 2011
`
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`Fingerprint Source Book – Chapter 1: Introduction
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`FSS
`
`Home Office Central Research Establishment (HO CRE) 1967 – 1988
`Home Office Forensic Science Service (FSS), Central Research and Support
`Establishment (CRSE) 1988 - 1992
`Aldermaston Laboratory closed (1992), Metropolitan Police Forensic Support
`Laboratory (MPFSL) absorbed by the FSS (1996). Fingerprint research
`subsequently split between FSS Lambeth and FSS Trident House,
`Birmingham.
`
`Early research also conducted by the Atomic Weapons Research
`Establishment (AWRE) under contract to CAST.
`
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`Fingerprint Source Book – Chapter 2: Finger mark examination techniques within scope of ISO 17025
`
`Chapter 2: Finger mark examination techniques within
`scope of ISO 17025
`
`2.1 Visual examination
`
`1. History
`
`1.1. Visual examination was the first technique proposed for the detection of
`fingerprints, with Henry Faulds suggesting the use of finger marks in
`blood, impressions in clay or marks left on glass for identification of
`criminals in his letter to the journal Nature in 1880. Many of the early
`landmark cases in fingerprint identification involved marks detected
`visually [1]; in Argentina in 1892 Vucetich used a mark deposited in
`blood on a door frame to disprove an account of a murder; in 1897
`fingerprints in blood on a book cover were used to identify a murderer in
`India; and in 1902 impressions of fingerprints in paint were used to
`identify a burglar in the first trial using fingerprint evidence in the UK.
`
`
`1.2 Detection of a mark by visual examination did not necessarily mean that
`it could be easily captured. In many cases the lighting conditions
`required to detect the mark were difficult to recreate and maintain for
`photography, but as the use of fingerprint evidence increased a range of
`techniques were developed or adapted for the photography of both
`developed and latent marks. Those described for operational use in 1954
`[2] included transmitted light, vertical/specular illumination, dark ground
`illumination, oblique illumination, oblique top illumination and duo
`filtering.
`
`1.3 Practical examples of the use of backlighting, vertical/specular
`illumination and oblique illumination were presented in subsequent
`publications [3,4]. The detection of fingerprints in both grease and dust
`was demonstrated using the range of lighting techniques above. Olsen
`[3] also recommended visual examination of metals and firearm articles
`for latent prints that may not be developed by powdering, with marks
`occasionally being etched into metal by the fingerprint constituents or
`ridge impressions left in the oil coatings often found on firearms. Pfister
`subsequently reported the application of specular lighting techniques
`using a semi-silvered mirror for the capture of latent fingerprints on
`glossy surfaces [5].
`
`
`1.4 Other photographic techniques such the use of polarising filters [6]
`began to be employed in the imaging of latent fingerprints, improving the
`contrast between the fingerprint ridges and the background by
`suppressing the reflections from the background regions. A combination
`of polarisation and specular reflection techniques has recently been
`suggested for the detection of latent fingerprints [7]. The use of specialist
`tilt/shift lenses has also been demonstrated for the capture of marks on
`mirrors, where the image of the mark may otherwise be obscured by
`background reflections [8].
`
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`Fingerprint Source Book – Chapter 2: Finger mark examination techniques within scope of ISO 17025
`
`
`1.5
`
`
`1.6
`
`It has also been proposed that marks detected by visual examination
`need not always be photographed in situ; if it is considered that
`powdering or chemical development would be of no benefit and
`photography is difficult, lifting of the mark may be carried out using either
`transparent lifting tape or gelatine lifters (black, white or transparent) [9].
`Lifting of latent marks, either after visual examination or as a speculative
`technique, should not be carried out as an alternative to treatments such
`as powdering if the application of a development technique is feasible.
`The Home Office Centre for Applied Science and Technology (CAST)
`has recently carried out a comparison of the effectiveness of gel lifting
`and powdering for development/capture of latent marks [10] and has
`demonstrated that powdering is the more effective process.
`
`It has long been recognised that in some circumstances latent
`fingerprints may be developed by the environment they have been
`exposed to and fingerprints developed by heat have been found on
`paper articles at arson scenes [3]. Recent studies by CAST and others
`have found that there are a wide range of mechanisms by which
`fingerprints can be developed by the soot and heat at arson scenes [11-
`14], and visual examination of articles recovered from such scenes is
`essential.
`
`
`
`2. Theory
`
`2.1 The principle of visual examination is to utilise lighting in such a way as
`to provide as much contrast as possible between fingerprint ridges and
`the background, if possible suppressing any patterned backgrounds. For
`the initial detection of marks this is done by trying different lighting
`angles, but once a mark has been located there are several techniques
`that can be used to capture it in the optimum way. Some of these are
`described below, together with the situations that they are most
`appropriate for.
`
`
`2.2 Oblique illumination
`Oblique illumination may be used to capture marks where fingerprints
`are deposited in dust. The low angle illumination is scattered by particles
`of dust on the surface being examined, resulting in more light reaching
`the imaging system from these regions than in areas where no dust is
`present.
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`Dust particles scattering Dust particles scattering
`
`incident lightincident light
`
`
`Schematic diagram illustrating the use of oblique lighting to detect marks
`deposited in dust
`
`
`2.3 Oblique illumination can also be used in the capture of fingerprint
`impressions in wax or putty. In this case the low angle illumination casts
`shadows in the depressions left by the fingerprint ridges, thus aiding in
`their visualisation.
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`Fingerprint Source Book – Chapter 2: Finger mark examination techniques within scope of ISO 17025
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`Imaging systemImaging system
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`Light sourceLight source
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`Light scattered Light scattered
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`towards imaging towards imaging
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`systemsystem
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`Impressions in substrate Impressions in substrate
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`with areas shadowed by with areas shadowed by
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`Schematic diagram illustrating the use of oblique lighting to detect marks
`left as impressions in a soft surface
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`Fingerprint Source Book – Chapter 2: Finger mark examination techniques within scope of ISO 17025
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` 2.4 Specular (oblique top) illumination
`Specular illumination can be used for latent marks or marks in
`contaminant on reflective surfaces. It is essentially the opposite of
`oblique illumination, with the light source being placed at a high
`illumination angle in close proximity to the imaging system. Where light
`falls upon a reflective region of the background, it is specularly reflected
`at an angle where the reflected light does not reach the imaging system.
`Where light falls upon fingerprint ridges, it is either scattered or diffusely
`reflected, resulting in some light being reflected to the imaging system.
`The ridges will therefore appear lighter than the background in the
`image.
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`Incident lightIncident light
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`Specularly reflected light –Specularly reflected light –
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`not reaching imaging systemnot reaching imaging system
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`Diffuse reflections from ridgesDiffuse reflections from ridges
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`towards imaging systemtowards imaging system
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`Schematic diagram illustrating the use of specular illumination to detect
`marks on smooth, reflective surfaces
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`2.5 This principle is utilised in the BVDA GLScan system, developed for the
`imaging of trace evidence lifted on black gelatine lifters [15].
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`2.6 Dark field illumination
`Dark field illumination is suited to cases where fingerprints in sweat, oil or
`grease are present on transparent substrates, such as glass or plastic
`packaging. The sample is illuminated from underneath at oblique angles.
`In regions with no fingerprint deposit, light is transmitted and does not
`reach the imaging system Where there is a fingerprint deposit present
`the light is scattered, some of it reaching the imaging system. The
`resultant image shows light fingerprint ridges against a dark background.
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`Transmitted lightTransmitted light
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`Transmitted lightTransmitted light
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`Transparent substrateTransparent substrate
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`ridges towards ridges towards
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`imaging systemimaging system
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`Schematic diagram illustrating the use of dark field illumination to detect
`marks on transparent substrates
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`2.7 Co-axial illumination
`Co-axial illumination can be used where a latent mark or a mark in
`contaminant is present on a patterned, reflective background. A semi-
`silvered mirror at 45º to the axis of the imaging system is used
`essentially to provide co-axial illumination. The incident light is reflected
`downwards onto the sample. Where it meets the reflective surface it is
`strongly reflected and some passes through the semi-silvered mirror to
`reach the imaging system. Where the light hits ridges, it is scattered or a
`diffuse reflection occurs. The amount of light reflected back towards the
`imaging system from these regions is correspondingly less, and the
`fingerprint will appear as dark ridges against a light background.
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`Several commercial systems have been developed incorporating co-axial
`or epitaxial illumination although these are mostly marketed for machine
`vision applications and none has been widely adopted for finger mark
`detection and imaging.
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`Imaging systemImaging system
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`Light sourceLight source
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`Strongly reflected light fromStrongly reflected light from
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`background reaching imaging background reaching imaging
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`Incident lightIncident light
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`Semi-silvered mirrorSemi-silvered mirror
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`Diffuse reflections from ridgesDiffuse reflections from ridges
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`Schematic diagram illustrating the use of co-axial illumination to detect
`marks on smooth, reflective surfaces
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`2.8 Polarised light
`Polarised light can also be used to detect a latent mark or a mark in
`contaminant on a reflective background. A linear polarising filter is used
`in front of the light source to produce linearly polarised light. When this
`reaches the reflective surface it is reflected and retains its polarisation.
`Where it hits the finger mark ridges it may be scattered or diffusely
`reflected, resulting in a depolarised component of light being reflected
`from the surface. A cross-polarised filter is placed in front of the imaging
`system, which blocks the specularly reflected light and allows a
`component of the de-polarised light through, resulting in an image with
`light ridges against a dark background.
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`Polarising filterPolarising filter
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`Linearly polarised Linearly polarised
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`incident lightincident light
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`Reflected light passing Reflected light passing
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`through polariserthrough polariser
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`Polarising filterPolarising filter
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`De-polarised light De-polarised light
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`diffusely reflected diffusely reflected
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`from ridges from ridges
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`Polarised light Polarised light
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`specularly reflected specularly reflected
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`from background from background
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`Schematic diagram illustrating use of cross-polarised light to detect
`marks on reflective backgrounds
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`3. CAST processes
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`3.1 The CAST Manual of Fingerprint Development Techniques [9] identifies
`five generic types of fingerprint that may be visible.
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`• Type 1 – where the fingerprint is present in a semi-transparent
`material, such as sweat, oil or grease.
`• Type 2 – where the fingerprint is deposited in a coloured material, such
`as blood, ink or paint.
`• Type 3 – where the fingerprint is in dust.
`• Type 4 – where the fingerprint is present as a result of a reaction
`between a fingerprint and the surface, e.g. fingerprints visible on
`ferrous, silver and copper articles as a result of surface corrosion or
`tarnishing.
`• Type 5 – where there are fingerprint impressions in wax or putty.
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`Subsequent to the work carried out on articles recovered from an arson
`scene [11-14], a further type is proposed.
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`• Type 6 – where fingerprints have been developed by the effects of an
`environment the article has been exposed to, e.g. fingerprints
`developed on paper by the action of heat.
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`Examples of all these types of mark are illustrated below.
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`e)
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`Different types of marks that may be detected by visual examination a) Type 1
`mark in grease on CD b) Type 2 mark in soot on mug c) Type 3 mark in dust
`d) Type 4 mark on metal sheet e) Type 5 mark in plasticine f) Type 6 mark
`developed by heat on paper.
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`3.2 The process recommended by CAST for all of these types of marks
`consists of examination under natural light, turning the article so that
`illumination falls on it from different angles. This should be followed by an
`examination using an even, white light source, again altering the angle of
`illumination from perpendicular to the exhibit to oblique.
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`3.3 Any fingerprints detected using this examination process should be
`imaged using the most appropriate technique outlined in the ‘Theory’
`section above.
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`4. Critical issues
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`4.1 Visual examina