Copyright
A. (Alfred) Lucas.

Forensic chemistry [electronic resource] online

. (page 9 of 23)
Online LibraryA. (Alfred) LucasForensic chemistry [electronic resource] → online text (page 9 of 23)
Font size
QR-code for this ebook


purpose by the paper manufacturer.

Testing of Ink. — The nature of the ink on a document
should as a rule be determined, since this may serve as an
indication of age or as a proof of alterations or additions.
The testing is carried out by applying minute drops of
various reagents to the writing by means of a capillary
pipette and examining the result with a lens, and this can
be done so carefully that any marks left are so small that



DOCUMENTS 91

it is difficult afterwards to find the spot tested. When
writing has been chemically tested a note should always be
made of the exact spots to which the reagents have been
applied and these should be indicated in the report.

It cannot be insisted upon too strongly that suspected
documents should be treated with the greatest care, and no
one who has not had considerable experience in delicate
manipulation should be allowed to test them. Sometimes
an alteration to a document consists of a few letters or
figures only, or even of part of a single letter or figure, and
unless the greatest precautions are taken, the disputed
portion of the writing will be so defaced as to become quite
useless as evidence. In cases of this nature it is inadvisable
to test the ink at all.

In view of the comparatively large number of reagents
for testing ink on documents recommended in various books,
perhaps it will be as well to state that very few are actually
required, the most useful being dilute hydrochloric acid
(strength not more than 5 per cent.), dilute sodium hydroxide
(strength about 2 per cent.) and a solution of bleaching
powder, or better, of sodium hypochlorite. Oxalic acid,
tartaric acid and acetic acid are occasionally useful sub-
stitutes for hydrochloric acid and may be employed in
greater strength than the mineral acid without fear of
injuring the paper. Sulphuric acid, although frequently
recommended, should never be used, since it will inevitably
seriously damage the document. This damage may not
take place at once, but only gradually, and hence may not
be apparent until some time afterwards. When testing
fresh or comparatively fresh ink, potassium ferrocyanide,
which is frequently emplo^^ed as a test for iron in ink, is
less valuable than sodium hydroxide, since it labours under
several disadvantages, one being that it readily decomposes,
giving the very reaction (a blue colour) it is used to test
for, and another that it reacts with any iron compounds
in the paper as well as with those in the ink. Also, since
potassium ferrocyanide solution is acidified with hydro-
chloric acid before use, this latter renders visible the blue
colour due to any provisional colouring matter in the ink,
which masks any other blue due to iron compounds. When



92 FORENSIC CHEMISTRY

testing old inks both potassium ferrocyanide and potassium
thiocyanate are necessary and are then to be preferred to
sodium hydroxide. When using these reagents a minute
drop of hydrochloric acid is first placed on the ink in order
to dissolve the iron, and this is followed by a drop of ferro-
cyanide or thiocyanate. Sodium hydroxide has also a dis-
advantage in the way it spreads on the paper, but the effect
of this may be minimized by using the smallest possible
quantity and by removing the excess with blotting paper
as soon as the result of the test has been noted. No matter
what reagent is used, it is a wise precaution to remove the
excess remaining after the reaction has terminated, by
means of blotting paper, or better to wash it off by applying
successive drops of water which are afterwards absorbed by
blotting paper.

Carbon ink is distinguished from most other writing
inks by the fact that it remains unaltered When treated with
a solution of bleaching powder or of sodium hypochlorite.
Other reagents are also without effect.

The fact already mentioned that carbon ink can readily
be removed from documents provides a good test for this
ink. A drop of water is placed on a small piece of filter
paper, which is then applied to the writing and pressed
down with the thumb-nail. If the ink is a carbon ink, a
little will generally come off and will be found as a black
stain on the filter paper and can be tested. Occasionally
an iron ink, especially an old iron ink, will transfer in the
same way, but the presence or absence of iron can readily
be ascertained by applymg a drop of hydrochloric acid,
followed by a drop of potassium ferrocyanide or of potassium
thiocyanate.

Both iron ink and logwood ink, unlike carbon ink, give
very marked positive reactions with various reagents. The
principal results are shown in the table opposite.

In several cases investigated alterations to documents
written with carbon ink have been made with an iron-tannate
ink containing a provisional blue colouring matter, and in
one instance a document written with carbon ink had been
altered twice, in one place with an iron-tannate ink and in
a second place with logwood ink. In another case a document



DOCUMENTS



93



written with iron-tannate ink had been altered with carbon
ink.

Many of the results of the chemical examination of ink
on documents, which are to be found in the literature of
the subject, have reference to an iron tannate ink without
any provisional blue colouring matter, and therefore are
very misleading, since practically all ordinary writing inks
now contain a blue colour.

It is sometimes suggested that in order to test the nature
of aniline ink on a document, or even of any kind of ink,
a press copy of the writing should be taken so that this may
be tested chemically instead of the original. This should



Keagent.


Iron-gall Ink

without Blue

Colouring Matter.


Iron-gall Ink

with Blue

Colouring Matter.


Logwood Ink.


Hydrochloric acid


slight yellow
stain


blue


red


Oxalic acid


bleaches


blue


red


Tartaric acid


bleaches


blue


light brown


Acetic acid


bleaches


blue


violet


Sodium hydroxide


reddish brown


reddish brown


brown


Potassium ferrocyanide(a)


blue


blue





Potassium thiocyanate (a)


red


red





Sodium hypochlorite . .


bleaches


bleaches


bleaches



(a) After the iron has been dissolved by a drop of hydrochloric acid.



never be done. In the case of aniline ink it is sometimes
allowable to take a copy of a few unimportant letters or
words, if such exist, but in no circumstances whatever should
a press copy be made of a suspected alteration or suspected
signature or date. As already mentioned, if the testing is
carefully done there need not be any disfigurement of the
document. With respect to violet ink only one substance
is generally employed, namely methyl violet, and therefore
as a rule chemical tests yield no useful results.

For blue inks different compounds are used, and some
of these may be distinguished from one another even when
in the form of writing. When dealing with blue ink the



94 FORENSIC CHEMISTRY

following caution should be noted : — An ordinary iron-
tannate ink containing a blue colouring matter if very
recent is blue, and when tested with hydrochloric acid,
oxalic acid, tartaric acid or acetic acid it remains blue or
may become still more blue, owing to the bleaching of any
colour due to the iron-tannate, and the consequent rendering
visible of all the blue already present. Such an ink too
gives a reddish-brown colour when tested with sodium
hydroxide. When blue aniline inks, which are sometimes
used for writing, are tested with these same reagents, they
also remain blue with the acids, and in some cases give a
reddish purple colour with the sodium hydroxide, and
therefore, unless care is taken, such an ink might be mistaken
for a very recent blue-black iron ink.

For red inks there are satisfactory tests. The dye
principally used for making red ink is eosine, but cotton
scarlet, ponceau scarlet or fuchsine might also be employed,
and the following method of distinguishing between them
when on a document may be mentioned: — With bromine
water eosine becomes yellow, but the red colour returns on
the addition of sodium hydroxide ; cotton scarlet also
becomes yelloAV with bromine water, but on the addition
of sodium hydroxide to the yellow spot a brown colour
is formed ; sodium hyroxide applied directly to the cotton
scarlet produces a puce colour which disappears after a
time ; with bromine water ponceau scarlet at first becomes
yellow and then bleaches ; bromine water turns fuchsine a
violet colour, which becomes yellow or orange on the addition
of sodium hydroxide.

Occasionally it is found that a few words or figures in
red ink are suspected because of their dark colour, but this
may simply be due to a black-ink pen having been used
by mistake at the beginning of the writing or to the pen
having been subsequently and inadvertently dipped into
black ink.

In one book dealing with questioned documents, the
chemical testing of ink is described as " quite simple," and
it is further stated that " the cost of the necessary material
and the time required to make oneself proficient as a capable
tester are so slight that even the small fee that would be



DOCUMENTS 95

charged by a chemist is scarcely worth paying." It is
certainly true that the cost of the reagents required is slight,
chiefly because the quantity used is so minute, and the
method of testing like everything else is simple when one
knows how to do it, but the way proposed of determining
the presence of acid in an ink on a document by placing
" the tip of the tongue to a thick stroke " cannot be recom-
mended, nor is it advisable to put so much water on a
document that some of it can subsequently be poured into
a test tube, as is advocated in the book in question. A
" point of a pin " as suggested as a means of applying acid
is also unsatisfactory. The only right way of testing ink
on a document is that already mentioned, namely to apply
an exceedingly small drop of the requisite reagent by means of
a fine capillary pipette, and to examine the result with a lens.

Pens. — The first steel pen on record was made in
England in 1780 and others were made and sold in 1803.
The first patent for the manufacture of metallic pens is
dated 1808. Machine-made pens were introduced in 1822.^
In England and many other countries the only pen now
used is the ordinary steel jDen, the quill pen formerly employed
having become practically obsolete, but in the East pens
analogous to the quill are still employed; thus in Egypt
a reed pen is very common, though it is being gradually
superseded by a special form of steel pen. The writing
made with these different kinds of pen can often be dis-
tinguished by the general appearance, the shading and the
width of the ink lines. Even writing made with different
pens of the same kind may be distinguished if the points
are of different fineness. It is a useful precaution in connection
with the examination of forged or anonymous documents
to ascertain whenever possible the kind of pen used by the
suspected writer.

Pencil Writing. — Pencils used for writing may be either
black-lead or they may be coloured, the colour generally
being violet, and such pencils are termed " indelible " or
" copying " or " copying ink " pencils, but blue or red
pencils are also used.

^ Encyclopaedia Britannica, 11th Edition. Cambridge, 1911,
Vol. XXI, Article " Pen."



96 FORENSIC CHEMISTRY

Black-lead Pencils. — Black-lead pencila were not known
before the discovery of graphite in Cumberland about 1560,
earlier pencils being made either of metallic lead or of a
lead alloy.

It is sometimes stated that it is impossible to distinguish
between one black-lead pencil and another when in the
form of writing, but C. A. Mitchell ^ has recently shown that
under certain conditions writing done with different pencils
may be differentiated both by microscopical examination
and by chemical tests.

For the microscopical examination a 1-inch objective
and a strong side light are employed. The variations in
the marks made by different pencils consist of {a) differences
in the colour and distribution of the pigment, (6) the presence
and nature of certain striations and (c) a brilliant lighting
effect sometimes observed on the paper. Mitchell states
that too much importance should not be placed upon
differences in the depth of colour observed, since under
variations of pressure marks from hard pencils may
resemble and may be mistaken for those made by soft
pencils.

The chemical tests applied to black-lead pencil writing
consist principally of tests for iron and chlorides, but may
include a test for sulphates and also a test with dilute nitric
acid. For iron a drop of 80 per cent, acetic acid or of strong
nitric acid is placed on the writing, followed by a drop of
potassium ferrocyanide. Different pencil marks show pro-
nounced differences in the colour produced. The presence
or absence of chlorides also serves to distinguish between
the writing done with different pencils. For this reaction
a drop of dilute nitric acid is applied to the writing and
silver nitrate solution is then added to the drop, which
should retain its globular form throughout the test.
A test for sulphates with nitric acid and barium chloride
or nitrate may also show differences, or sometimes there
is a difference in the behaviour with dilute nitric acid
alone.

Copying Ink Pencils. — The only reference to this subject

^ Black-lead Pencils and their Pigments in Writing. C. A. Mitchell.
J. Soc. Chem. Ind., 1919, p. 383t.



DOCUMENTS 97

that can be traced is a recent paper by C. A. Mitchell. ^ The
tests applied are both microscopical and chemical. When
examined with the microscope definite differences in colour
may sometimes be seen with writing made with different
pencils. Different pencil marks also show characteristic
differences when tested with different solvents. Water,
alcohol, ether and acetic acid should all be tried, a drop
of the solvent being placed on the writing and the result
observed with a lens. It should be noted whether there
is any solution of colour and whether this solution is immediate
or not, and finally the drop should be soaked up with a
small piece of filter paper. The residue left on the paper,
particularly that left after acetic acid, should be examined
microscopically when graphite if present will be seen and a
difference in the amount may be found in the case of different
pencils.

To test the colour chemically a little is extracted by
placing a drop of alcohol or acetic acid on the writing and
then absorbing it by means of filter paper. To the spot of
colour thus obtained various reagents are applied, such as
nitric acid, hydrochloric acid, stannous chloride, sodium
nitrite with acetic acid and sodium hypochlorite with acetic
acid and the colour effects produced observed with a lens.
The residue left on the paper after the removal of the colour
with acetic acid should be tested for iron with a 5 per cent,
solution of potassium ferrocyanide. Another useful test is
that for chlorides, and for this a drop of silver nitrate is
applied directly to the writing.

In a murder case Mitchell gave evidence that writing
in copying ink pencil on some fragments of partially burnt
paper from the grate of the room where the body was found
gave identical results when tested with that of a copying
ink pencil belonging to the accused person, who finally
admitted that the writing had been done by him. The
accused, however, was acquitted on other grounds.^

Mitchell has shown that writing done with copying ink
pencils is very little affected when immersed in sea water
for long periods.^

1 Copying Ink Pencils and the Examination of their Pigments
in Writing. C. A. Mitchell. Analyst, 1917, pp. 3-11.

8



98 FORENSIC CHEMISTRY

Handwriting. — In the examination of suspected forgeries
and anonymous documents a study of the handwriting is
of great importance. It seems at first sight to be a very
simple matter to determine whether one specimen of writing
is in the same hand as another or not, and it is quite a
common experience for the ordinary man to be appealed to
on such a question, and most people are quite ready to give
a decision. Even the few who disparage handwriting experts
because of the mistakes that have sometimes been made
employ the method of comparison of handwriting in their
own private affairs, and notice, and even act upon, resem-
blances and differences found. The untrained person,
however, bases his comparison upon the broad features of
the writing only and does not as a rule pay any attention
to details. Since, however, the aim of the forger is to
deceive, a clever forgery, in order to pass muster at all,
must necessarily resemble in its general aspect the writing
forged, and therefore something more than a superficial
likeness or difference is required before any useful opinion
can be pronounced regarding the genuineness or otherwise
of a specimen of writing. The study of handwriting to be
of any value must be conducted according to strictly scientific
methods, which can only be done by those possessing special
experience, and hence in all cases of doubt or dispute regarding
the authenticity of documents the matter should be referred
to an expert, for not only may he discover characteristics
in the handwriting that make its origin certain, but not
infrequently small points in connection with the writing,
the paper or the ink, which would be passed unnoticed by
an untrained observer, will be found and may prove of
considerable value as evidence. Thus in a certain suspicious
letter that was being examined it was stated that it had been
commenced in a train and finished afterwards in the house,
but the internal evidence did not bear this out, the writing
being very regular and uniform and no part of it showed
any signs of having been done in a moving train and a similar
pen and ink had been employed throughout. A mere
opinion, however, that different documents are or are not
in the same handwriting is of very little value unless the
expert is able to demonstrate this in his report or in Court,



DOCUMENTS 99

and when the similarities or differences are substantial this
can usually be done by means of enlarged photographs.

All writing may be considered as consisting of a series
of strokes, and it is not necessary to know what the strokes
mean or how to pronounce them in order to compare them,
all that is required being a sufficient knowledge of the
language to recognize and follow the same letter or word
whenever it occurs.

In theory, the examination of one form of writing should
not present any greater difficulty than the examination of
any other form of writing, since whatever language a man
uses, he unconsciously imparts to the writing certain
characteristics which are personal and peculiar, and by
means of which his individuality is expressed and may be
recognized. In practice, however, the author has found
Arabic-writing much more difficult to examine than either
English or French, probably because of his imperfect acquaint-
ance with Arabic,

When deahng with suspected forged or anon3^mous docu-
ments the known and genuine writing is first carefully
examined and all the important characteristic features
noted. The forged or anonymous writing is then similarly
treated. Small agreements or differences such as those of
size, slant or angle should generally be disregarded, since
few people write the same letter or word in an absolutely
identical manner on two different occasions, complete
identity being generally a proof of forgery by means of
tracing or transfer. It is only a mechanical process like
printing or photography which produces results that never
vary. Small agreements or differences in non-essentials
between two specimens of writing and which are of no value
as proving the identity or non-identity of the writers, and
which should not be taken into account, are a frequent
cause of the unfortunate conflict of opinion between hand-
writing experts, one basing his conclusions on facts which
undoubtedly exist but which the other rightly refuses to
regard as essential. The expert should always mention in
his report that he only claims identity or non-identity between
the writings compared in respect to certain fundamental
characteristics and not with regard to small superficial details.



100 FORENSIC CHEMISTRY

A frequent criticism made against handwriting experts
is that too few documents are examined and that a certain
letter or word stated to be a characteristic of a particular
writing may occur in a large number of other cases. This
criticism is based on a misconception of the expert's position.
In order to prove the identity of the writing on two different
documents, the expert establishes the presence in each of
the documents of a number of characteristics or peculiarities,
as many as possible being unusual or uncommon. ReUance,
however, is not placed upon the presence of any one charac-
teristic, since one or even more may be accidental or may
occur in other writings, but reliance is placed upon the
presence of the same combination of the same character-
istics in each of the two documents, care being taken that
the characteristics are sufficient in number to exclude the
possibility of chance. The absence of fundamental differences
is also established. These are the same principles that are
employed in personal identification and in the finger-print
system. Thus measurements of various parts of the body,
the colour of the hair and eyes, deformities and scars are all
personal characteristics, but no single one is sufficient by
itself to establish identity, which can only be done by a
combination of characteristics. In the Bertillon system of
identification a maximum of eleven different measurements
are taken, and although many hundreds of thousands of
people have been examined only a very few cases are known
in which two different persons have been found to possess
the same combination of measurements, and in such cases
other features, and notably the finger prints, are different.
As a rule fewer characteristics than eleven are quite sufficient
to prove identity, and even one characteristic if it be very
marked and uncommon is almost enough. With regard to
the finger-print system, Locard states ^ that identity is
proved by the agreement of twelve or more characteristics.

The expert should be particularly careful to avojd being
misled by a general resemblance of style due to nationality
or other cause and should never forget that writing done
by different members of the same family is frequently super-

^ L'Enquete criminelle et les Methodes scientifiques. E. Locard.
Paris, 1920, pp. 128-9.



DOCUMENTS 101

ficially much alike. It has been noticed too that many
Egyptian clerks writing English often have a general simi-
larity of style. As an example of a national characteristic
the French custom of making a bar across the down stroke
of the figure 7 may be mentioned. In England such a
feature would be very unusual and therefore characteristic,
but in a country such as Egypt where there is a considerable
French influence, it is very common and as a rule need not
be specially taken into account.

In the case of anonymous documents not only should
the writing be examined and compared with that of the
suspected person, but the paper and ink should also be
carefully examined, since these may provide important clues.
In many instances the writer of anonymous letters is never
traced, but in a few cases very definite proof of identity may
be obtained, and even when this cannot be done it is some-
times possible to clear a person who has been wrongly sus-
pected. In a country like Egypt evidence of nationality,
which can sometimes be proved from the writing, spelling
or composition, may be very useful.

In one instance investigated, in which it was important
to trace the origin of an anonymous document, this was
done from the evidence afforded by the ink, that on the
document and some found in a bottle in the hou-e of the
suspected person, when examined and compared, being
characteristic and identical ; it was a blue-black writing
ink of poor quality and contained a large amount of finely
divided insoluble matter, and had probably been made
from ink powder. In another case, well-marked finger prints
were found. In another case an anonymous letter was
written on a half sheet of note paper, on which a faint
reversed impression of a name and address could be deciphered
and which had manifestly been present as a stamped heading


1 2 3 4 5 6 7 9 11 12 13 14 15 16 17 18 19 20 21 22 23

Online LibraryA. (Alfred) LucasForensic chemistry [electronic resource] → online text (page 9 of 23)