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Ink marks made with a compound consisting of the
combination of iron and an infusion of galls or its
equivalent （a tanno…gallate of iron ink）； as treated
with certain chemicals； change from a compound with
color to a chemical compound； with no color。 Nothing
has in fact been absolutely removed or eradicated；
but it is a mere change of form； a sort of re…arrangement
of the particles； the ingredients which formed
the original color being still present； but in such a
condition that they are invisible to the eye。 A restoration
of the invisible ink marks so that they can
be observed； becomes possible by the use of chemical
reagents and is the reverse of the one of erasure or
bleaching； and changes the constituents again into a
compound which has color from the one which had
none。 It does； not； however； reproduce the exact composition
originally existing。 Such a reagent simply
goes to the basis of the material as first used； takes
up what was left and reforms the particles sufficiently
to make them abundantly recognizable。 An apt
illustration of these chemical changes of color is found
in what is known as the phenolphtalein test solution；
which is colored deep purplish…red by alkali hydrates
or carbonates； and then by the addition of an acid
rendered colorless； to be again reddened by an over…
plus of the alkali and so on ad infinitum。
A popular material for the purpose of making
chemical erasures is chlorinated lime or soda； which
becomes more active by first touching the ink mark
to be removed with a one half strength solution of
acetic acid； this hastens the liberation of chlorine
gas； THE active agent which causes the 〃bleaching〃
to take place。 Hydrogen peroxide； also a bleaching
compound； is less rapid in its action than chlorinate
of soda； the same may be said of combinations of
oxalic and sulphurous acids。
The most effective re…agent for the restoration of a
chemically 〃bleached〃 iron ink mark is the sulphide
or sulphuret of ammonia （it has several names）。 This
penetrating chemical blackens metals or their salts；
whether visible or not； if brought together。 It must
not be used by direct contact； the best and safest
plan being to place a quantity in a small saucer； to be
set on the floor of a closed box； to fasten to the box
lid the specimen to be operated on； in this way the
restoration is due to the fumes of the chemical and a
possible danger of destruction of the specimen much
lessened； especially if the marks are very light or delicate
ones。 The restoration of color under particular
conditions may also be obtained by treatment with
tannic acid； potassium ferro…cyanide （acidulated） or a
weak solution of an infusion of galls。
CHAPTER XVIII。
INK CHEMISTRY。
SOME OBSERVATIONS AS TO CHEMICAL EXAMINATION OF
INK MARKS BY ALLENERASING OF INKS BY CHEMICAL
MEANSAPPROVED CHEMICAL TESTS IN THE
ASCERTAINMENT OF INK CONSTITUENTS。
A COMPILATION of the methods of Robertson；
W。 Thompson （Lord Kelvin）； Irvine； Wislar； Hoffman
and others； relative to the chemical examination of ink
marks； is to be found in 〃Allen's Commercial Organic
Analysis。〃 Their experiments； however； date back
many years ago； a few of them before the time of the
use of the 〃anilines〃 for added color。 The so…called
〃alizarin〃 ink referred to has now become obsolete。
The following is the citation in part：
〃In chemico…legal cases it is sometimes of
importance to ascertain the nature of the ink used；
to compare it with specimens of writing of known
history； and to ascertain the relative ages of the
writings。 A minute inspection should first be
made with a magnifying power of about 10 diameters；
and any peculiarities of color； lustre； shade；
etc。； duly noted； and where lines cross each other
which lie uppermost。 The examination is often
facilitated by moistening the paper with benzine
or petroleum spirit； whereby it is rendered semi…
transparent。 The use of alcohol or water is inadmissible。
〃Valuable information is often obtainable by
treating writing or other ink…marks with reagents。
Some inks are affected much more rapidly than
others； though the rate of change depends greatly
on the age of the writing。 Normal oxalic acid （63
grammes per litre）； or hydrochloric acid of
corresponding strength； should be applied to a part of
the ink marked with a feather or camel…hair brush
（or the writing may be traced over with a quill
pen）； and the action observed by means of a lens；
the reagent being allowed to dry on the paper。
Recent writing （one or two days old） in gallic inks
is changed by one application of oxalic acid to a
light gray； or by hydrochloric acid to yellow。
Older stains resist longer； in proportion to their
age； and a deeper color remains。 Log…wood ink
marks are mostly reddened by oxalic acid； and
alizarin marks become bluish； but aniline inks
are unaffected。 With hydrochloric acid； logwood
ink marks turn reddish or reddish…gray； alizarin
marks greenish； and aniline ink marks reddish or
brownish…gray。 The treatment with acid should
be followed by exposure to ammonia vapors； or
blotting paper wet with ammonia may be applied。
Thus treated； marks in logwood ink turn dark
violet or violet…black。 The age of ink marks very
greatly affects the rate of their fading when treated
with dilute ammonia； the old marks being more
refractory。 The behavior of ink marks when
treated with solution of bleaching powder is often
characteristic； the older writings resisting longer；
but unless the reagent be extremely dilute； writings
of all ages are removed almost simultaneously。
Hydrogen peroxide acts more slowly than bleaching
solution； but gives more definite results。 After
bleaching the mark by either reagent； the iron of
the ink remains mordanted on the paper； and the
mark may be restored by treatment with a dilute
solution of galls； tannic acid； or acidulated ferro…
cyanide。 The same reagents may be used for restoring
writing which has been faded from age
alone。
〃When ink marks have been erased or discharged
by chemical means； traces of the treatment
are often recognizable。 After effecting the erasure
the spot is often rubbed over with a powdered alum
or gum sandarac； or coated with gelatin or size。
The bleaching agents most likely to have been
used are oxalic； citric； or hydrochloric acid； bleaching
powder solution； or acid sulphite of sodium。
Moistened litmus paper will indicate the presence
of a free acid； and in some cases treatment with
ammonia fumes will restore the color。 The presence
of calcium； chlorides； or sulphates in the
water in which the paper is soaked will afford some
indication of bleaching powder or a sulphite having
been used。 Potassium ferro…cyanide will detect
any iron remaining in the paper。 Exposure to
iodine vapor often affords evidence of chemical
treatment； and other methods of examination
readily suggest themselves。〃
M。 Piesse； in the Scientific American； is authority
for a method of removing ink； found on 〃patent〃
check paper：
〃Alternately wash the paper with a camel's…
hair brush dipped in a solution of cyanide of
potassium and oxalic acid； then when the ink has
disappeared wash the paper with pure water。〃
Inks of the tanno…gallate of iron family； whether
containing 〃added〃 color or not； can be more or less
〃erased〃 by chlorinate of lime or soda； in the
presence of a weak acid。 These chemicals do not；
however； materially affect the prussian blue inks；
which require solutions of hydrate of potash or soda。
Real indigo can be removed by chloroform； morphine
or an aniline salt （indigo and aniline both owe their
names to the same Portuguese source）； which possess
the rare property of dissolving pure indigo。 Such
combination； if refractory in the presence of permanganate
of potash with sulphuric acid； must be followed
by an application of sulphurous acid。 In like
manner； inks composed of by…products of coal tar； can
be effectively treated； when irradicable with plain
water or soap and water。
The erasure and removal of most inks from paper
can be accomplished by the application of the chemicals
heretofore enumerated。 The requirements in
this direction of some inks； however； though of rare
occurrence； are to be met by the employment of other
and particular reagents。
Many of the tests specified in the Allen citation to
determine the character of ink constituents； if made
alone are practically valueless； because the same behavior
occurs with different materials employed in the
admixture of ink。 To avoid error in judgment the
operator should verify if possible by confirmatory
tests。 Thus； in the one for logwood； sulphurous acid
will cause a logwood ink mark to turn yellow； mercuric
chloride； orange； tartar…emetic； red； and if the
marks are faded ones； solutions of sulphate of iron
or b