TECHNIQUE OF PRINTING AND SCRUTINIZING FINGER-PATTERNS
There are important points connected, with the printing of
finger-patterns, especially for legal investigation, which come now to
be considered. A human finger, as we have seen, is not, for printing
purposes, just like a lithographic stone, a box-wood engraving, or
a plate of zinc, steel, or copper. In ordinary printing, especially
of high-class and delicate engravings, the quality and fluency
of ink, the smoothness of surface and hygrometric conditions of
paper--due sometimes to local atmosphere, and sometimes to climate
generally--the skill of workmen, all the conditions co-operate
in producing variations, slight it may be, but noticeable in the
results obtained. In the case of finger-prints we might also have
to consider the willingness or unwillingness of the subject having
his finger-prints officially taken. A finger--even that of a dead
person--is compressible, while retaining on the whole the pattern of
its furrows and ridges, and hence under fairly similar conditions,
the printed products may be somewhat different in appearance. The
same fact would apply, no doubt, also to impressions taken from an
indiarubber stamp, made, we shall suppose, for stamping purposes in
regard to documents, in imitation of a particular finger-print pattern.
Greater compression tends to flatten out the ridges and to narrow
the intervening grooves, while it may also tend, especially when
associated with over-inking, to obliterate some of the characteristic
ramifications of the pattern. But, again, the finger of a living person
is usually in a state of physiological activity. It swells or shrinks,
drying up or exuding moisture from its many pores, which facts, however
minute and insignificant they may appear to the uninstructed, to the
trained dactylographer they leave a most interesting and significant
record behind.
Examine carefully a ridge which has been printed--and, if possible,
photographically enlarged--at various periods not long apart, and the
pores with which it is dotted will be found, while retaining their
relative positions, to vary somewhat in their degree of patency. A
single ridge might be compared to a naval cruiser, the numerous funnels
of which are not all belching forth smoke at the same time, but one
is almost smokeless while its neighbour is quite active. Those pores
which have been copiously emitting sweat are seen, when imprinted,
to be larger than those that were inactive. An imaginary case was
once suggested to me as a final blow to finger-print identification.
A certain Mr. William Sykes is officially known to be recruiting
his valuable health at one of His Majesty’s sanatoriums for people
of his profession. That celebrated artist’s “thumb”-print, however,
has been found liberally spotted all over the scene of some tragic
area of crime. What is to be said? Well, the prodigality of display
of the well-known sign-manual, in circumstances when gloves are
almost invariably now worn by experts, might well arouse suspicion
in itself, but it would easily be found in such a case that the
pattern had been prodigally repeated with too great fidelity in the
matter of sweat-pores, which, in the case of an active burglar, who
is a sober, hard-working fellow in spite of his faults, would vary
with each successive imprint, in a way that no manufacturer of bogus
“thumb”-prints could easily follow.
The fact that a finger--a clean finger--is naturally, to some slight
extent, greasy, partly from sebaceous secretion, enables the expert
dactylographer by various chemical and mechanical means to obtain a
pretty clear vision, even in minute detail, of what before had been
quite invisible. A mere accidental smudge from a slightly oily palm
or finger, if imprinted on glass, japanned tin, varnished or polished
wood, etc., may have its invisible lineations brought out by dusting
gently upon it some light powder of appropriate colour. Dr. René
Forgeot, in 1891, first called attention to this method of bringing out
latent imprints, and my friend, Dr. Garson, of this country, gave it
further developments.
In my _Guide_ I have mentioned some of my own results with
modifications of these methods.
On a pane of glass which a malign finger is suspected to have touched,
a fine black powder gives vivid and beautiful results, the sooty matter
clinging to and revealing the oily surface of the lineations in very
full detail. In my article in _Nature_ of 1880 a sooty imprint is shown
to have helped an innocent man to establish his innocence, but in this
case the imprint was quite direct. The powder should be gently blown
over, or dusted lightly on to the greasy impression, with a soft camel
hair brush which is perfectly clean and dry. Care should be taken not
to breathe on the glass, or a damp, smeary effect may result. I have
not found sable brushes act so well as those made of camel hair, a
fact which their structure under the microscope helps to explain. (See
frontispiece.)
The best treatment of a greasy smudge on a dark ground, say the surface
of a japanned cash-box, marble slab, school slate, or enamelled door
panel, is carefully to dust over the object with a fine white powder,
such as the ordinary tooth-powder of the chemists, or still better, as
I find, with the light carbonate of magnesia. In one sense this may
be said to yield a _negative_ print, but an important qualification
arises. The patterns now in white are the ridges which before were
black, while the furrows remain dark as at first. In a smoked glass
print the white ridges have not imparted something to the glass,
but have simply removed the carbonaceous deposit previously there.
Practically, however, the whitened ridges have the quality of a
negative imprint, as previously described.[D]
[D] See _Guide to Finger-Print Identification_ (fig. 12)
Greasy finger-marks may also be acted on chemically, so as to bring
out details by the application of osmic acid. If there is any olein or
oleic acid in the mark, as there generally is in human finger-marks,
the acid deepens the tone of the almost invisible lines into a brownish
hue, revealing all their richness of detail. I have succeeded in
etching finger-marks of this kind on glass by means of hydro-fluoric
acid. They remain quite indelible in all their details so long as the
glass itself endures. The patterns thus etched can be very well brought
into view by painting a dark background on the reverse, or pasting
dark paper behind. There is a clear layer of the skin in both palms
and soles, the fat of which is eleidin. That particular kind of fat
does not stain with osmic acid in the usual way. The sweat of palms and
soles is not supposed to contain any fat at all, but there would seem
to be some faint trace of it in sweat. The greasy surface of the skin
as a rule comes from the sebaceous glands, as previously described.
When clean palms leave a greasy smear, as they often do, I think the
greasiness must generally come by transmission from other parts of the
body, or from contact with foreign greasy substances, which are common
enough.
For those who wish to study dactylography, the apparatus is neither
complicated nor expensive. A good pair of compasses, a botanical
lens, a school slate or tin plate or porcelain tile, a small pot of
fine printer’s ink, and an ink-roller or photographer’s “squeegee”
will suffice for most purposes. For the expert who must make fine
measurements of enlarged photographs, and perhaps defend them under
keen forensic criticism, one or two instruments are required, presently
to be described.
The ink may be daubed evenly and thinly on the slate, tile or plate,
but it is better to use a small printer’s roller for the purpose. Avoid
all fluff, hairs, or grit, which thoroughly spoil any print. The roller
should always be scrupulously cleaned before laying aside, and it is
well to provide a tin case for its reception. The remaining stock of
ink should be carefully levelled a-top, and covered with a drop or two
of linseed or other oil, which will preserve it in good and workable
condition for a long time. Reeve’s Artists’ Depôts, Ltd., 53 Moorgate
Street, London, supply an excellent quality of ink for this purpose,
in flexible tubes, at sixpence each, and the same firm can generally
provide the rollers or squeegees used by photographers, which serve
very well. In an emergency I have made serviceable ink with burnt cork,
lamp soot, even shoe-blacking, using a good smooth and even cork as a
roller. Wax casts, which should occasionally be made for study, can be
made with the sheets of wax used greatly, at one time, for the making
of artificial flowers. Excellent casts can also be made with putty,
gutta-percha, sealing-wax, or hard paraffin, such as is used to encase
the modern candle. Very excellent imprints of this kind have been left
by burglars on candles they have used.
Some useful practical hints as to how finger-prints may be photographed
and enlarged for police purposes are supplied by Inspectors Stedman and
Collins, in an official work by Sir E. R. Henry, _Classification and
Uses of Finger-Prints_; and others occur in _Daktyloskopie_, published
in Vienna. Finger-marks on plated articles, when placed squarely with
the camera in a strong side light, will appear light on a dark ground.
The instructions in such a case are: “Focus sharply. Should, however,
the mark be too faint to be clearly seen on the focussing screen, a
piece of printed paper can be placed around the mark to focus by, but
this should be removed before exposing the plate, otherwise halation
will set in and obscure some of the lines in the finger-mark.” The
plate done in this way gives a negative result, so that a transparency
must be made and used so as to convert that into a positive print.
The fingers and thumbs may each be printed separately. For
identification the serial order of fingers must be retained on the
record. The official method in England is to print four fingers of each
hand simultaneously, adding the right and left thumb to each respective
section of the register. In addition, each thumb and finger is
imprinted by rolling it slightly, which gives an enlarged area for the
display of the more important linear elements in each finger pattern.
The prisoner signs this sheet, and also adhibits an imprint from his
right forefinger under the signature.
The highly-glazed papers now so much used for half-tone photographic
reproductions are not, in my experience, particularly good for ordinary
impressions. The surface of any paper used should be fairly smooth, the
texture firm, tough (not brittle), durable, and the colour white, as
photographs for enlargement as judicial exhibits may be required.
Great care is now taken officially to secure the correct order of
fingers, as on that the validity of the method depends, and the whole
utility of the classification.
Inspectors Stedman and Collins, in the work just quoted, state that
when finger-prints are required to be produced as evidence in a court
of justice, “they are first enlarged 5 diameters direct with an
enlarging camera. The negatives are afterwards placed in an electric
light enlarging lantern, with which it is possible to obtain a
photographic enlargement of a finger-print 36 inches square, such a
photograph being as large as is ever likely to be required.”
In my _Guide to Finger-Print Identification_ (p. 62) I have advocated
uniform enlargement of all such exhibits on the decimal or metric
system, and hope that international agreement on this point may be
secured. Apart from criminal services its scientific utility would
ultimately be very great. The objection that an English jury would
dislike being confronted with the technicalities of a foreign and
“mathematical” system is very easily met. An English jury--and no jury
in the world is fairer or clearer-headed--would only, in any case, have
to compare two figures _similarly enlarged_, one being that of the
accused person’s fingers, taken while in custody, and the other, either
a similar official record of another date, or a smudgy mark from some
blotting-pad, window-pane, drinking-glass, bottle, or the like. The two
exhibits, paired for comparison, would have been enlarged exactly on
the same scale, whatever that scale might have been. For purposes of
judicial comparison, therefore, English terms and English instruments
might be used throughout, and no inconvenience could be felt by the
most insularly prejudiced jury that could possibly be got together.
When a photographic enlargement has been made, it is necessary to
be able readily to test its conformity with the enlargement to be
compared with it, or if there be not strict agreement, to allow for
and calculate the admitted discrepancy. This may easily be done by an
application of the “rule of three.”
MALE.
H.C.R. No._____________
|
Name________________________| Classification No.___________
|
Aliases_____________________|
|
Prison______________________|
Prison Reg. No. ________ RIGHT HAND.
-------------+-----------+-------------+------------+--------------
1.--R. Thumb.|2.--R. Fore|3.--R. Middle|4.--R. Ring |5.--R. Little
| Finger.| Finger. | Finger.| Finger.
-------------+-----------+-------------+------------+--------------
| | | |
| | | |
| | | |
| | | |
-------------+-----------+-------------+------------+--------------
(Fold.) | | | | (Fold.)
-------------+-----------+-------------+------------+--------------
Impressions to be so taken that the flexure of the last joint shall
be immediately above the black line marked (Fold). If the impression
of any digit be defective a second print may be taken in the vacant
space above it.
When a finger is missing or so injured that the impression cannot be
obtained, or is deformed and yields a bad print, the fact should be
noted under _Remarks_.
LEFT HAND.
-------------+-----------+-------------+------------+--------------
1.--L. Thumb.|2.--L. Fore|3.--L. Middle|4.--L. Ring |5.--L. Little
| Finger.| Finger. | Finger. | Finger.
-------------+-----------+-------------+------------+--------------
| | | |
| | | |
| | | |
| | | |
-------------+-----------+-------------+------------+--------------
(Fold.) | | | | (Fold.)
-------------+-----------+-------------+------------+--------------
LEFT HAND. | RIGHT HAND.
Place impressions of the four | Place impressions of the four
fingers taken simultaneously. | fingers taken simultaneously.
---------------------------------+---------------------------------
|
|
|
|
---------------------------------+---------------------------------
_Impressions taken by_ _Rank_ _Prison_
-------------------------------------------------------------------
_Governor’s Signature_ _Date_
-------------------------------------------------------------------
_Classified at H.C. Registry by_ _Date_
-------------------------------------------------------------------
_Tested at H.C. Registry by_ _Date_
-------------------------------------------------------------------
[Illustration: REDUCED COPY OF POLICE REGISTER FORM]
_Prisoner’s Signature_________________
+-------------------------+
| Right forefinger print. |
| To be impressed |
| =immediately= after |
| signature is written. |
+-------------------------+
| |
| |
| |
| |
+-------------------------+
------------------------------------------------+------------------
NAME | =REMARKS.=
------------------------------------------------|
Year of Birth Complexion |
------------------------------------------------|
Hair Eyes |
------------------------------------------------|
Height ft. in. |
------------------------------------------------|
L { |
a { *Sentenced at |
s {---------------------------------------------|
t { |
{ " on |
C {---------------------------------------------|
o { |
n { " to |
v {---------------------------------------------|
i { |
c { " *for |
t {---------------------------------------------|
i { |
o {* Give offence in full, and if remanded only,|
n {substitute “Remanded” for “Sentenced.” |
------------------------------------------------|
|
|
|
It may be necessary to test the concurrence of curved lines in two
exhibits similarly enlarged. At one time I used strips of plumber’s
lead, placed edgeways on the curved lines to be compared. They could
be flexed so as to show the various sinuosities, however complex,
but leaden tapes cannot readily be made to retain the form imparted
to them. Copper wire I found to be stiffer, but it readily warps off
the plane. An excellent way is to draw on transparent paper a line
corresponding to the curved line seen underneath. The transparency is
then transferred and adjusted to the other enlargement, the curves of
which should be seen to be congruent. The instrument called “flexible
curves” which is used by engineers and mechanical draughtsmen I at last
tried, and found it to be exceedingly serviceable for such comparisons.
The pattern “=B=,” self-clamping, 12-inch size, is for most cases the
most suitable. Other patterns are made also, in sizes of 9 and 18
inches. The “=B=” pattern has a flexible steel strip, like the lead
tape just mentioned. After the curve or series of sinuosities has
been adjusted correctly, the shape is rigidly retained by means of
a stiff-hinged link-work arrangement attached by tabs. The strip of
steel should not be pressed down between two tabs, and when bending
or straightening out the instrument one should do so bit by bit,
beginning at one end and continuing onwards from there. This useful
self-clamping instrument used to be supplied by Mr. Wm. Brooks,
scientific instrument maker, 33 Fitzroy Street, Tottenham Court Road,
London. Another instrument of this kind, the “Curve Rule” is sold by
Mr. W. Harling, 47 Finsbury Pavement, E.C., and is figured here.
[Illustration: FLEXIBLE CURVES.]
[Illustration: HARLING’S J. R. B. CURVE RULES.]
In dealing with such _approximate_ curves as one finds among the
lineations of finger-prints, one is not supposed to apply strictly
mathematical principles. The lines, for example, have breadth, but not
quite invariable breadth. We must, therefore, avoid treating them, as
a beginner fresh from the schools is apt to do, as ideal concepts.
The simpler terms, however, as used by a teacher of drawing, with
the provisos already hinted at, will serve very well to guide one’s
efforts, or to explain one’s own conceptions before a magistrate or a
jury.
Besides the congruity of the curves, one has further to test the single
lineations, their junctions, number, and character. An excellent way to
envisage these is to make alternate linings with blue and red pencil,
to represent them as they seem. To do this effectively one may single
out a special measured square, or circle, or parallelogram, of the
enlarged figure. Proceed then, quite ignoring, if need be, all great
curvatures, to consider the lines as simple curved or straight lines,
and analyse them into composing elements, like twigs of a tree or the
characteristics of a runic alphabet. The result will be, perhaps, like
the figure on the next page.
It will now be quite easy to orient, or place correctly in space,
the corresponding part of the other print--if it really does
correspond--and a similar “rune” should result. One may afterwards
follow out each recognized lineation into further complexities or
joinings, as you might trace out a railway line with its various
junctions in a map.
[Illustration: DIAGRAMMATIC ANALYSIS OF LINEATIONS IN A RESTRICTED
SECTION.]
A photographic enlargement, meant for forensic use, ought not to be
marked or soiled in any way, but dots of coloured chalk or ink might be
placed along the margins to denote where imaginary ruled lines might
begin or end. One might also use glazed tissue paper, ruled in squares,
or with eccentric circles like the mileage lines in a map of London.
By the use of these placed over the figure one might verify particular
coincidences or demonstrate discrepancies.
When the skin-pattern is impressed upon soft sealing-wax, clay, putty,
and so on, the _relievo_ image produced is different in this way from
an ordinary ink-printed pattern. The convex ridges are now concave
furrows, while the hollows are changed into heights.
In both kinds of impressions a reverse or _mirror_ pattern is produced,
a matter of some practical importance. This effect may, or may not
again be reversed in the photographic process. It is not impossible, in
such circumstances, that a suspect’s finger might be confused with a
resembling “mirror” pattern, which was really not his own.
I have thought that the word _verso_, used technically for the reverse
of a coin or medal, might be usefully employed in dactylography for the
reverse or mirror image of a finger-pattern when printed. A technical
word for the indented impression made by a finger on wax and the like
is also wanted. Now geologists use _-lite_ as a terminal to express the
impression or cavity which had been formed in a rock, when soft, by the
impressed body of an organism. Hence the word _dactylolite_ might be
used to denote an indented impression of a finger.
[Illustration: KEW MICROMETER.]
In making measurements of exhibits, the Kew micrometer devised by Sir
Joseph Hooker is of much service. It is figured here, and has the
useful quality of rendering measurements at the same time in both the
English and decimal systems.
For the method of encircling suspect smudges, either before or after
enlargement, and measuring from one fixed centre by the Kew micrometer
or ordinary compasses, I have devised a disc of glass such as is used
in microscope slides, and about the size of half-a-crown. In the centre
is a conical pit into which one leg of the compass rests. Precise
centring is thus obtained without the slightest risk of damaging the
photographic or other exhibit by the sharp point of the compasses,
which have, at the same time, free swing. These were prepared for me by
Mr. Franks, optician, Stoke-on-Trent, and cost very little.
[Illustration: GLASS DISC CENTRED (enlarged).]
In all measurements close to a fork or junction, as in the crook of
the letter =Y=, care must be taken in counting the lines below or
above the fork. Ambiguity readily arises, with a train of resulting
discrepancies. Other ambiguities also occur which require mention in
a word or two. In deciphering an ancient manuscript blurred, mouldy,
mayhap worm-eaten, doubts may arise as to which of two or three
possible words or letters may have been intended. One looks for some
rationality in the author’s writing, but in finger-prints there can
be no such help. In manuscripts the problem may not directly be as
to a word, but only as to a letter, but that single letter, read
differently, may change the tenor of a passage. Is ={deformed G}=
to be read as =C= or as =G= or as =O=? Is ={deformed E}= to be
read as =E= or as =B=? So Fork is liable to be read as Pork.
Now, a very similar difficulty frequently occurs in reading a blurred
finger-print, and such evidence should be scrutinized with the greatest
vigilance, and all really doubtful cases should be discarded as useless
in evidence. While the obscurity is sometimes merely due to defective
printing, there are several patterns of frequent occurrence which
are liable to be read variably. This was discussed at some length in
chapter iii. of the _Guide_. There is a tendency so to view blots or
blurs in such a case, that the cloudy spots become a weasel or even a
whale. In Japan there are artists’ wine-parties, where a common game
is to make an accidental splash of ink or colour, which is passed on
to the next guest, who in turn converts it by one or more strokes of
the brush into a figure of some character. Some years ago, I gave
to a young men’s meeting a lecture on Ghosts, in which I showed a
collection of ink-splashes produced without design, some of which were
quite strikingly artistic in their suggestive impressionism. Hence
the importance of clear printing, vigilant scrutiny of exhibits to be
compared, and the attention of a well-informed judge and intelligent
jury.
In certain circumstances, when a suspected person has been arrested
abroad or at a distance, it may be desirable to compare his fresh
finger-prints broadly with that of some well-known criminal whose
register has been long in the hands of the police. This want led me
to suggest, in 1905, that photo-telegraphy, in one of its forms, might
be brought into use. Many improvements have been made since then, and
it is now, I think, quite feasible to secure and transmit to a great
distance outline lineations quite good enough for use at a preliminary
enquiry, previous to a remand or committal.