A. C. (Arthur Columbine) Wright.

Simple methods for testing painters' materials online

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A. C. WRIGHT, M.A. (OxoN.), B.Sc. (LOND.)








[All Rights remain with Scott, Greenwood & Co.]



THE materials employed in painting are,
perhaps for several reasons, peculiarly liable
to adulteration, and it is not uncommon to
find one substance entirely replaced by
another of lower value. This book is de-
signed to enable the painter and dealer to
test and value the materials they buy, and
the manufacturer and dealer the samples
submitted to them, in the simplest manner,
both in regard to practical properties and
composition, the latter term being here used
more in a manufacturing than a purely
chemical sense.

I have addressed myself throughout to the
layman, so that the chemist will find much
superfluous matter, but will also, I hope, find



points of interest. I have endeavoured to
treat the subject in such a manner that the
descriptions might enable any intelligent
person to execute all the tests and obtain
reliable results. But whilst the descriptions
of methods will be found very detailed, I
have made no attempt to give any but the
most necessary explanations of the chemistry
of the processes. I have also dealt only with
materials in every-day use, and have given
the greatest attention to points of the most
practical importance.

Several of the processes described, though
they may have been in use, have not, I
think, hitherto been published. I trust that
these may be found reliable and useful.


March, 1903.


INTRODUCTION. Section 1. Necessity for Testing 2. Stan-
dards 3. Arrangement 4. General Preliminary
Remarks ... ... ... ... ... ... ... 1-5

Chapter I. THE APPARATUS. 5. The Working Place 6.
Colour and Paint Sampling Apparatus 7. The Scales
8. Weights 9. Measures 10. Thermometers 11.
Specific Gravity Apparatus 12. The Bunsen Burner
13. Flasks 14. Bottles 15. Beakers 16. Evapo-
rating Basins 17. Test Tubes 18. Watch Glasses
19. Glass Rods 20. Platinum Wire 21. Tripod Stands
and Wire Gauze 22. India-rubber Tubing 23. Mouth
Blowpipe 24. Filter Funnels and Filter Paper 25.
Cleaning Glass Apparatus 26. Cost 6-30

Chapter II. THE REAGENTS. 27. Meaning of Term 28.
Water 29. Sulphuric Acid 30. Nitric Acid 31.
Hydrochloric Acid 32. Acetic Acid 33. Ammonia-^-,
34. Caustic Soda 35. Sodium 36. Caustic Potash
37. Potassium Iodide Solution 38. Lead Acetate
Solution 39. Potassium Ferrocyanide (Yellow Prus-
siate) Solution 40. Lime Water 41. Uranium Acetate
42. Absolute Alcohol 43. Methylated Spirit 44.
Rectified Benzol 45. Ether 46. Aniline Oil 47.
Refined Linseed Oil 48. Terebine and Quick Gold
Size 49. Alkali Blue 31-38


Dry Colours. 50, 51. Shade 52. Staining Power 53.
Covering Power 54. Miscibility 55. Permanence
56. Under Special Conditions 57. Influence on
Drying of Oils 58. Influence on the Durability of
Paint 38-58


Stiff Paints. 60. Shade 61. Staining Power 62.
Covering Power and Miscibility 63. Permanence
64. Drying Power 65. Durability 58-65

Liquid and Enamel Paints. 66. General 67. Drying,
Face and Shade 68. Flash Point 69. Durability
and Preservative Action 70. Stoving Enamels ... 65-73

Oil Varnishes. 72. Drying, Colour and Brilliance 73.
Durability 74. Consistency 75. Specific Gravity
76. Viscosity 77. Flash Point 78. Mixing Varnishes
79. Stoving Varnishes 80. Oil Lacquers 81. Paper
Varnish ... 73-86

Spirit Varnishes. 82. French Polish $3. Knotting Var-
nish 84. White and Brown Hard Spirit Varnishes
85. Spirit Stains and Lacquers 86,87

Driers. 86. Patent Driers 87. Dry Driersr-88. Terebine 87-89

Putty ... 90

Linseed Oil 90. General 91. Haw Linseed Oil 92,

Refined Linseed OU 93. Boiled Oil 90-96

Turpentine. 94. American Spirits of Turpentine 95.

Russian Turpentine ... ... ... ... ... 97-99

Water Stains ... ... , ... ... 99

Chapter IV. THE CHEMICAL EXAMINATION. 97. General 100

Dry ' Colours and Paints. 98. Extraction of Oil from
Paints 99. Examination of the Oil 100. Extraction
of Varnish... ... 101-105

White Pigments and Paints. 101. White Lead 102.
White Sugar of Lead 103. Zinc White 104. .
Whiting, Paris White 105-113

Yellow Pigments and Paints. 105. Litharge 106.
Chrome Yellows 107. Zinc Yellow 108. Perma-
nent Yellow, Yellow Ultramarine 109. Ochres and
Yellow Paints 110. Dutch Pink 113-120

Blue Pigments and Paints. 111. Chinese and Prussian
Blue 112. Brunswick Blue, Mineral Blue, etc.
113. Copper Blues, Blue Verditer 114. Ultramarine,
Lime Blue 115. Blue Lakes 120-124

Green Pigments and Paints. 116. General 117. Chrome
Greens 118. Zinc Greens 119. Guignet's Green-
Oxide of Chromium 120. Green Ultramarine, Lime


Green 121. Aniline Greens, Green Lakes, Lime
Greens 122. Mineral Green 123. Green Verditer
124. Emerald Green 124-132

Red Pigments and Paints. 125. General 126. Vermilion-
ettes 127. Permanent Reds, Vermilion Substitutes
128. Vermilion 129. Red Lead, Orange Lead
130. Venetian Red, Indian Red, Red Oxides 131.
Persian Red, Chinese Red 132. Rose Pink 132-141

Brown Pigments and Paints. 133. Siennas, Umbers,

Vandyke Brown ... ... ... ... ... ... 142

Black Pigments and Paints. 134. Ivory Black, Drop

Black 135. Lamp Black, Vegetable Black, etc. ... 142-144

Oil Varnishes. 136. General, the Detection of Resin ... 145-148

Spirit Varnishes. 138. French Polish and Knotting

Varnish 149-151

Linseed Oil. 139. General, Detection of Small Quantities

of Mineral Oil 151-154

Turpentine. 140. Determination of Purity 154-156

INDEX ... . ? . ... 157-160


i* Necessity for Testing* There are two
ways of discovering that a substance employed
in the arts and manufactures is not what it
is supposed to be. It may be used, when a
result differing from the expected will show
that some one of the materials employed was
deficient in quality ; the particular substance
which caused the bad result has then to be
found, and possibly the work done over again.
This method leads to trouble and expense.
The alternative method consists in testing
every substance before it is used or sold,
immediately it comes into the hands of the
manufacturer, dealer or consumer. If the
testing is efficient, there is then no oppor-
tunity for surprises when the materials are
employed. The preliminary trouble, and pos-
sibly expense, may be greater, bub in the long
run the economy is considerable. Broadly

speaking, it may be said that no one should



use or sell materials, which he buys or makes,
without first ascertaining that they satisfy his
requirements. The testing may range from
a simple inspection to an exhaustive analysis,
whichever may be required to elucidate the
quality of the' substance.

The quality of the materials employed in
painting depends, in the first place, on certain
practical properties shade, drying-power, etc. ;
when these are satisfied it becomes a question
of ascertaining by chemical tests whether the
substance will fulfil the requirements of dur-
ability and permanence, which cannot well be
tested in a practical manner on every occasion.
The chemical tests are also employed because
they show, in a more delicate and precise
manner than the practical tests, the presence
of adulterants, and thus the true quality and
value of the substance.

2. Standards* Certain properties of the
materials, which cannot conveniently be ex-
pressed in figures shade, drying-power must
be estimated by comparison with standards,
which are samples of the particular substance
chosen as answering all requirements, and to
which all future parcels, made or bought, will


be expected to conform. The importance of
keeping standards of paints, dry colours,
varnishes, etc., cannot be over-estimated.
Standards of dry colours may be preserved in
lever-lid tins, of paints in collapsible tubes.
It is also advisable to keep samples of each
delivery of bought materials and each batch of
manufactured. The former may probably be
destroyed at regular intervals.

3. Arrangement* The tests to which the
ordinary materials used in decorative paint-
ing are subjected, in order that an estimate
may be obtained of their purity and quality,
may be divided roughly into practical and
chemical (and physical) methods. This divi-
sion is adopted here merely for the sake
of convenience, % and it will be found that
methods are included in one section which
perhaps should more properly be placed in
the other. The " practical methods " relate to
those properties of pigments, paints, oils, etc.,
which are of immediate importance in their
application, such as the shade and staining
power of paints, the drying of boiled oil, and
the durability of varnishes. The chemical and
physical methods are designed to elucidate the


actual composition of the various substances,
and thus to give an estimate of their value,
and consequently of the manner in which
they will answer the requirements of practice.

In the first place, the apparatus employed
in the different tests will be described, and
precise directions given for its use. The
practical methods, treated generally, will
then follow, and finally the chemical tests
for each substance.

4. General Preliminary Instructions* Be-
fore commencing the description of the ap-
paratus, it is thought to be expedient to
make certain preliminary remarks of general
application :

1. Before performing any operation, read
all the details given concerning it, and if
you are not perfectly familiar with the use
of the apparatus, refer to that section which
describes it. Have everything required for
a test ready to hand before you begin.

2. First try all tests on materials whose
composition you know (if possible), until you
can carry them out in a satisfactory manner,
then apply the test to the sample whose
composition or value you are examining. It


is no waste of time to repeat a test several
times until you know exactly how to perform
it. Whatever written instruction may be
given, ease and rapidity in working can only
be attained by practice.

3. Perfect cleanliness is always an absolute
necessity. Without cleanliness, doubtful or
erroneous results, which may have serious con-
sequences, must occur sooner or later. Given
cleanliness and care in working, there follows
a just confidence in the results. This condition
of cleanliness must be observed in carrying out
all tests, practical and chemical. Fortunately,
a training in colour-sampling does not lead to
laxity in this respect.

4. When a case of adulteration appears to
be detected, do not immediately make a charge
of fraud, which is a serious matter, and, if there
should have been a mistake in testing, might
lead to very unpleasant consequences. Gen-
erally speaking, it would not be wise to make
a charge of fraud except on the evidence of a
trained chemist, to whom such cases should be
referred, if redress cannot be obtained in some
other way. .



5. The Working Place should be set apart
for the purpose of testing materials and kept
for this purpose only. It should consist of a
bench about three feet high, two feet wide and
six feet long ; a hard wood or lead-covered top
is desirable. A wooden top should be merely
oiled, not painted. Beneath the bench should
be a cupboard and drawers to hold the appa-
ratus, and store the samples and standards.
At one end may be shelves to hold bottles
of the necessary reagents. At the other end
should be a water-tap and small sink with
waste pipe. If these are not provided, a large
stone or glass bottle, provided with a tap at the
bottom, standing on a shelf about 8 to 10 in.
above the bench, may be substituted, and the
waste water may be collected in a wooden pail
placed so that its rim is, level -with the top of

the bench. Of course any regular means of



supplying water may be omitted, but the omis-
sion will be extremely inconvenient. In this
case, as in all others, it will be found advisable
to make convenient arrangements at the outset,
since the tendency is always to neglect to per-
form operations the means for which are not
at hand. If water is not readily accessible,
the apparatus will not be cleaned as often as
is necessary (which is whenever it has been
used), and mistakes will follow in due course.

A gas supply ending in two \ or f in.
nozzles must be provided. The nozzles may
be at the back of the bench, about 1 in.
above its surface, or they may be underneath
it in front, with a corresponding f in. hole
through the top of the bench to admit the
necessary india-rubber tubing. On the whole,
the best position for both taps and nozzles is
the back of the bench.

The lighting of this working place is most
important. The best arrangement is to have
a plain or frosted glass window (kept clean),
with an uninterrupted north aspect, at the back
of the bench. If this cannot be obtained, the
window should be so placed as to receive as
little direct sunlight as possible. It is almost


as difficult to match and test colours in strong
sunlight as in semi-darkness. Means for
screening sunlight from the window should
be provided. Most forms of artificial lighting
have their disadvantages ; perhaps the
best of the ordinary sources of light is
the incandescent gaslight.

6. Colour and Paint Sampling Ap^
paratus. For sampling dry colours,
small palette knives (4 or 5 in.) are
most convenient ; they must be kept
perfectly clean and smooth by means
of bath-brick or other similar material.
For paints 6 and 7 in. knives may be
required, and, occasionally, larger sizes.
A stout 6 in. knife, ground down on
the grindstone, so that it tapers from
the original width near the handle to
about i in. at the point (see Fig. 1),
PIG is very useful. The metal must not
be reduced in thickness in the grind-
ing. This taper knife enables quite small, but
sufficient, quantities of colour to be ground
in oil, and thus leads to economy in time and

For most purposes paints may be sampled


on white marble slabs or white glazed earthen-
ware tiles. A large slab and muller will be
required for grinding hard substances (siennas,
ochres, etc.) in oil. A small hand paint-mill
may also be useful.

An oil bottle provided with a dropping tube
is required. Take a piece of glass tubing
(about J in. wide), make a notch with a
triangular file at one side of the tube (not all
round) about 2 in. from the end, hold the
tube in the fingers, with one hand at each side
of the notch, and close to it, then snap the
tube ; the end will thus be cut off square. In
the same manner then cut off a piece about 12
in. long, hold this horizontally over the flame
of the Bunsen burner (par. 12) until it is heated,
then bring it into the flame near the top, so
that the tube is heated about 3 in. from one
end. Keep the tube slowly revolving in the
fingers until the glass softens and begins to
fall in, then slowly draw out the tube, so that
the drawn out portion is 2 to 3 in. long.
Remove from the flame, continue to hold in
the fingers until the glass is hard, then put
aside to cool. When cold, cut the tube (as
before) with the file in the middle of the con-


stricted portion, then hold each end of the
long tube in turn in the flame, with the tube
nearly vertical, until the glass at the end just
softens and the narrow end forms quite a
small orifice. This tube may then be used for
delivering a certain number of drops of oil
to a dry colour or paint on the tile. If the
finger is just moistened and held on the upper
end it is easy to regulate the number of drops
which fall from the narrow end.

Small tins, ranging in size upwards from
2 in. deep and 1^ in. wide, may be used for
mixing liquid paints, etc. The paint is mixed
up in these by means of a palette knife or
stout iron wire hammered out flat at the end.
Liquid paints, lacquers, etc., are put to dry on
strips of tin, which may be obtained from
tinners' waste, and may be used in almost any
size from 2J by 1^ in. upwards. Strips of
glass,- about 3 to 4 in. wide, are very con-
venient for the drying tests of varnishes and
oils. Whilst the tin would be thrown away
after use, the glass strips should be put to
soak in strong soda, then very thoroughly
washed and dried before being again used.

The stone slabs, earthenware tiles and mix-


ing tins should be cleaned by means of cotton
waste and turpentine. The cleaning is very
much easier of accomplishment if the paints
are never allowed to remain on the articles
longer than is absolutely necessary.

7. The Scales* There will be required an
ordinary pair of scales, capable of weighing up
to 4 lb., with the corresponding set of weights ;
no further description is needed here. In
addition, an accurate balance, capable of
weighing to 0*001 gram (1 milligram), and of
carrying 50 grams in each pan, with the pans
movable, is necessary. It is much better to
purchase a balance provided with a glass case,
which protects it from dust and damp. If a
glass case is not provided, the balance should
be covered with a tin case when not in use.
A suitable balance, with a glass case, can be
purchased from any dealer in chemical appar-
atus for about fifty shillings. This balance
must be placed on a firm support, where it is
not shaken by persons walking across the floor
of the room. A very good position is a shelf
fixed to a wall ; this is, of course, not suitable
if the wall is shaken by machinery. The
balance will only weigh accurately if the cen-



tral pillar is strictly vertical, i.e., when the
beam is horizontal, the pointer must be at the
centre of the scale. This condition is generally
obtained by making the base-board horizontal,
which is done by means of the levelling screws,
L, under the balance case and a spirit level.

FIG. 2.

The screws must be adjusted so that the spirit
level shows the base-board to be level from
side to side, and also from back to front. If
the balance is not provided with levelling
screws, it must be made horizontal in some
other manner (by wedging up), and then fixed.
When once fixed and adjusted, a balance is


not lightly to be disturbed. Some means is
always provided for correcting the balance
when it is out of adjustment, i.e., when the
pointer does not give equal swings on each side
of the scale whilst there are equal weights in
the two pans. This means of adjustment, in a
balance of the type mentioned here, generally
takes the form of small nuts, N, on screws at
each end of the beam. When the base-board
has been fixed in a horizontal position, and the
scale pans and beam carefully dusted, turn the
handle or screw, H, at the foot of the pillar,
which lifts up the beam on the central knife
edge, and thus sets it swinging. Note the
number of divisions on each side of the
centre of the scale, S, to which the pointer
swings. If it swings to the same extent on
each side, the balance is in correct adjust-
ment. This will not generally be the case
when the balance is first set up. The side
of the balance to which the pointer swings
further is the lighter, therefore screw out a
little further the nut on the screw at that
end of the beam. Set the balance swinging
again, note the extent of the swing on each
side, and continue to move the nut until the


pointer swings exactly to the same extent on
each side. Screwing out the nut on one end
of the beam gives the same result as screwing
in the nut at the other end. From time to
time the balance will require cleaning ; take it
apart, dust it carefully, then replace the parts
and adjust as above described. Never put
anything on the pans, or take anything off,
without first stopping the motion of the balance
by turning the screw at the base of the pillar,
in order to bring the beam on to its supports.
In weighing, the weights on each pan are equal
when the pointer swings to the same extent on
each side of the scale.

8. Weights. The metric system of weights
and measures is now used for scientific pur-
poses, whilst the older British systems are still
employed in commerce. It matters little which
system is employed in the operations to be
described in this book. The writer finds it
convenient, as a rule, to use the metric weights
and measures for operations conducted on a
small scale, but avoirdupois weights and the
ordinary fluid measure for operations on a
larger scale. Thus there are required : a set
of gram weights ; a box containing the follow-


ing is suitable : 50, 20, 10, 10, 5, 2, 1, 1, 0'5,
0-2, 0-1, 0-1, 0-05, 0'02, O'Ol, O'Ol gram ; a set
of avoirdupois weights from 2 Ib. down to J oz.
For the gram weights may be substituted a
set of grain weights containing the following :
100, 50, 20, 10, 10, 5, 2, 1, 1, 0'5, 0'2, 01, 01.
It may occasionally be necessary to convert
grams to grains and vice versa ; the following
relations between the two systems may be
employed :

1 gram = 1543 grains.
1 grain = O0648 gram.
1 avoirdupois ounce = 28'29 grams.

In order to preserve the accuracy of a set
of delicate weights, and to use them without
error, it is necessary to observe certain pre-
cautions : In weighing an object of unknown
weight, put the weights on the scale pan in
their proper order, beginning with the highest ;
as a rule, do not try to find short cuts. Al-
ways return each weight to its proper place
in the box ; if you do not, the next time the
weights are required, you are liable to put the
wrong ones on the scale pan. No weight
should ever be put down on the table, it may
only be on the scale pan, in its proper place



in the box, or in the act of being moved from
the one to the other. Always pick up weights
with the pincers provided in the box, and
never with the fingers.

9. Measures* The fluid measures required
are 2 oz. and 1 oz. conical glass measures of
the ordinary druggists' pattern (Fig. 3) and 100
c.c. and 10 c.c. measures of the cylindrical form

FIG. 3.

FIG. 4.

(Fig. 4). When most liquids are put in glass
vessels, they rise up the sides to a certain
extent, so that the level of the liquid is
higher on the walls than in the centre of the
vessel. In using a measure there might there-
fore be uncertainty as to which portion of
the surface is to be brought into line with
the division on the measure ; the lowest por-


tion of the surface, seen on looking horizon-
tally at the measure, is to be brought into
line with the division marked on the measure.
For certain purposes, in which small quantities
of liquid have to be measured and added in
succession to another liquid, a burette is the
best instrument to use. A burette is a long
glass tube, provided with a tap at the bottom,
and graduated downward from the top. A
50 c.c. burette divided into two-tenths of a c.c.
would be suitable for our purpose ; to support
it a stand with a clamp would be desirable.
The burette is used as follows : it is washed
out with water, allowing the water to drain
out thoroughly, then washed out with a little
of the liquid which is to be used in it, which
is also allowed to drain out. It is then filled,
the liquid given time to run down the walls,
and its position in the tube noted (remember-
ing that the graduations run downward). The
liquid is then ran off through the tap for the
purpose required, and finally the level of the
liquid again noted ; from the difference in the
two levels the quantity of liquid used is found.
10* Thermometers* For the purposes of the
present book, thermometers on Fahrenheit's


scale are most suitable ; there will be necessary
one instrument with a scale going up to 220 F.
and a second with a scale up to 600 F. The
form of thermometer with a milk-glass back
and the scale engraved on the stem is the
best. Thermometers must never be heated to a
temperature higher than that to which they are
graduated. Before using a thermometer, it is

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Online LibraryA. C. (Arthur Columbine) WrightSimple methods for testing painters' materials → online text (page 1 of 15)