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LIGHT AND COLOUR THEORIES
[Illustration: TINTOMETER. Form of Instrument for Opaque Observation.]
[Illustration: Reproductions of some Medals awarded to JOSEPH W. LOVIBOND’S
Method of Colour Analysis FOR Scientific and Commercial Purposes.]
LIGHT AND
COLOUR THEORIES
and their Relation to Light and
Colour Standardization
By
JOSEPH W. LOVIBOND
ILLUSTRATED BY 11 PLATES COLOURED BY HAND
[Illustration: Logo]
London
E. & F. N. SPON, Limited, 57 HAYMARKET
New York
SPON & CHAMBERLAIN, 123 LIBERTY STREET
1915
CONTENTS
PAGE
List of Plates vii
Purpose ix
CHAPTER I.
Introduction 1
CHAPTER II.
Evolution of the Method 5
CHAPTER III.
Evolution of the Unit 9
CHAPTER IV.
Derivation of Colour from White Light 11
CHAPTER V.
Standard White Light 14
CHAPTER VI.
Qualitative Colour Nomenclature 17
CHAPTER VII.
Quantitative Colour Nomenclature
CHAPTER VIII.
The Colour Scales 28
CHAPTER IX.
Colour Charts 31
CHAPTER X.
Representations of Colour in Space of Three Dimensions 34
CHAPTER XI.
The Spectrum in relation to Colour Standardization 36
CHAPTER XII.
The Physiological Light Unit 45
APPENDIX I.
Colour Education 59
APPENDIX II.
The Possibilities of a Standard Light and Colour Unit 69
APPENDIX III.
Dr. Dudley Corbett’s Radiometer 83
Index 89
ERRATA.
Plate I. Newton’s Theory. The Indigo line is erroneously placed
between the Violet and the Red; it should be between the Blue
and the Violet.
Page 40.--_Fifth line from the bottom, for_ Fraunhoper _read_
Fraunhofer.
_To face p. vi., Lovibond, Light and Colour Theories._] [P.R. 1317
LIST OF PLATES
TO FACE
PAGE
Plate I. Six Colour Theories 4
" II. Circles Illustrating Absorption of White Light 11
" III. Diagram Illustrating Analysis of White Light 13
" IV. First System of Charting Colour 31
" V. Second System of Charting Colour 33
" VI. Six Tintometrical Colour Charts 39
" VII. Two Circles 40
" VIII. Absorption Curves of Dyes 76
" IX. Fading Curves of Dyes 78
" X. Comparison Curves of Healthy and Diseased Blood 80
" XI. Specific Colour Curves of Healthy and Diseased
Human Blood 82
PURPOSE
The purpose of this work is to demonstrate that colour is a
determinable property of matter, and to make generally known methods
of colour analysis and synthesis which have proved of great practical
value in establishing standards of purity in some industries.
The purpose is also to show that the methods are thoroughly scientific
in theory and practice, and that the results are not likely to be
changed by further discoveries. Also that out of the work done a new
law has been developed, which the writer calls the Law of Specific
Colour Development, meaning that every substance has its own rate of
colour development for regularly increasing thicknesses.
THE THEORY.
Of the six colours in white light--red, orange, yellow, green, blue
and violet; Red, Yellow and Blue are regarded as dominants, because
they visually hold the associated colours orange, green and violet in
subjection.
An equivalent unit of pure red, pure yellow and pure blue is adopted,
and incorporated into glass. The unit is multiplied to obtain greater
intensities, and divided to obtain lesser intensities.
The coloured glasses are called absorbents. The red absorbent transmits
violet, red and orange, but the red ray alone is visible as colour,
until the other absorbents are superimposed, and the character of the
group of rays changed. In the same way yellow transmits orange and
green, and blue transmits green and violet, whilst the yellow and blue
alone are visible as colour. Orange, green and violet are here called
subordinates, which may be developed as follows:--
Or. = R. + Y. Gr. = Y. + B. Vi. = B. + R.
Twenty-five years’ experience in the application of the theory and the
method to the requirements of practical work, have given no reason for
change. Following will be found a list of awards from International
Juries and Scientific Societies, also a list of industries in which the
writer’s method is giving entire satisfaction.
Awards by International Juries.
St. Louis 1 Silver Medal.
2 Bronze Medals.
Brussels 1 Gold Medal.
3 Silver Medals.
Turin Diploma of Honour.
1 Gold Medal.
1 Silver Medal.
Awards by Scientific Societies.
Sanitary Institute of Great Britain--
_Bronze_ Medal for Colourometrical Water Analysis.
Royal Sanitary Institute--
_Bronze_ Medal for Measuring Smoke Densities.
International Congress on School Hygiene--
_Bronze_ Medal for Colour Educator.
Royal Sanitary Institute--
_Silver_ Medal for Colour Educator.
Smoke Abatement Society, Sheffield--
_Diploma_ for System of Colour Measurement.
Royal Sanitary Institute--
_Bronze_ Medal for Quantitative Estimation of Colour Blindness.
Franco-British Exhibition--
_Gold_ Medal for Colour Educator.
International Medical Congress--
_Bronze_ Medal for Tintometer as Medical requisite.
Royal Sanitary Institute--
_Silver_ Medal for recent developments.
Royal Sanitary Institute--
_Silver_ Medal Corbett’s Radiometer.
Formal Adoption of Tintometer Standards by--
The Petroleum Industry.
The Massachusetts Board of Health.
The International Association of Leather Trades Chemists.
The Inter-states Cotton Seed Oil Association.
The Bureau of Engraving and Printing, China.
In general use by the following Industries--
Brewing and Malting.
Tanning.
Wine and Spirit Merchants.
Dyeing and Printing.
Paint, Oil and Varnish Merchants.
Millers.
Water Works Chemists.
Ceramic Works.
For estimating per cent. of Carbon in Steel.
For estimating per cent. of Ammonia.
For estimating Colours for Anthropological Classifications.
For estimating Smoke Densities.
For estimating Haemoglobin in the Blood.
For estimating Colour of Whale Oil, etc., etc.
THE METHOD.
The colour composition of any object may be measured by superimposing
units of different colours until the colour of the object is matched. A
convenient apparatus is furnished for this purpose. The composition of
the colour is learned by merely reading the markings on the glasses.
It is of course necessary that in the isolation of colour rays,
some unit for measuring the intensity of both light and colour be
established. As will be explained later, all such units are necessarily
arbitrary. In this method the unit has been established by taking the
smallest amount of colour easily perceptible to the ordinary vision.
This unit or “one” is divided into tenths in the darker shades, and
hundredths in the lighter scale. One one-hundredth is the smallest
amount of colour measurable by a normal trained vision.
When equivalent units in the three colours are superimposed, their
equivalent value (not their aggregate value) represents so much white
light absorbed. For instance, 2 R. + 2 Y. + 2 B. absorbs two units of
white light.
When the absorptive power of the colour standards is less than the
intensity of the light, associated white light remains.
JOSEPH W. LOVIBOND.
The Colour Laboratories,
Salisbury.
_December, 1914._
Light and Colour Theories
CHAPTER I.
Introduction.
It may at first appear strange that colour, one of the most important
indices of value in the Arts, Manufactures, and Natural Products,
should have no common nomenclature or reliable standard for reference,
the reproduction of a given colour depending for exactitude on the
memory of a sensation; whereas this branch of science requires a
physical means of recording a colour, with a power of recovery. It
remains to be shown that this power of record and recovery is possible,
and depends only on the observance of a few simple natural laws easy of
application.
The study of colour is carried on by two principal methods: the
spectroscopic, where the colours are partially separated as a
continuous band by a regular variation in their indices of refraction,
the colours gradually merging into each other by overlapping in
opposite directions; or by absorption, where a colour is developed by
absorbing its complementary, and is isolated as a single or complex
colour. This latter is nature’s own method.
It is necessary to touch on some theoretical differences which exist
between Scientists and Artists, as to which are Primary colours, as
confusion of this character retards investigation. Scientists adopt
Red, Green, and Violet as Primaries, regarding all other colours as
mixtures of these; whilst Artists and Colourists adopt Red, Yellow and
Blue as the Primaries, and all other colours as made from them.
The theory of the Scientists is based on the phenomena developed by
mixing coloured lights taken from different parts of the spectrum.
This is a method of synthesis, each added colour being a progressive
stage towards the complexity of white light. In this case the colour
developed is that of the preponderating ray of a complex beam. The
theory of the Artists is based on the phenomena developed by mixed
pigments. This is a method of analysis, tending towards ray simplicity,
each added pigment reducing the complexity of the colour developed by
its power of selective absorption.
The theoretical differences between the two schools appear to have
arisen from supposing that a given colour developed by the two
methods should correspond; but considering the differences in their
ray composition, this would be impossible, for although both may be
describable by one general colour term, as for instance a Red, they
would be of two varieties. It remains to be shown that one theory may
cover both sets of phenomena.
The Red, Green, and Violet theory appears to be based on two principal
assumptions: first that there are only three fundamental colours;
and second that the rays taken from different colour areas are pure
colours. Both assumptions are open to question. In regard to the first,
there is no difficulty in isolating six colours; and as to the second,
it can be demonstrated that the colours do overlap in every part, with
a double overlapping in the middle colours, and are therefore not
simple but complex.
PAST THEORIES.
In a work of this nature it is unnecessary to deal minutely with the
theories which have been adopted from time to time since Newton’s
discovery of the continuous spectrum. It will, however, be useful to
touch on the principal points where theorists are agreed, and also on
some of their points of difference, the latter in order to find, if
possible, the causes of their difference.
TABLE I.
----------------+-----+-------------------------------------------------
| No. |
| of | Primary Colours.
|Rays.|
----------------+-----+-------------------------------------------------
Newton (later) | 7 | Red, Orange, Yellow, Green, Blue, Indigo, Violet
| |
Werner | 6 | Red, Orange, Yellow, Green, Blue, Violet
| |
Newton and | |
Helmholtz | 5 | Red, Yellow, Green, Blue, Violet
(early) | |
| |
Hering | 4 | Red, Yellow, Green, Blue
| |
Chevieul, | |
Brewster, Hay, | |
Redgrave, Field | 3 | Red, Yellow, Blue
| |
Young, Helmholtz| |
(later) | 3 | Red, Green, Violet
----------------+-----+-------------------------------------------------
Note to Plate I.
The respective positions of the primaries of each theory in
regard to the whole cycle of distinguishable colours are
illustrated above, and the primaries of each theory are shown
in their several spectrum positions, the spectrum being shown
as bent in circular form.
The six principal theories of primary colours are given in Table I,
and illustrated on Plate I, with the names of the primaries of each
theory opposite the names of some of their principal advocates. It
should not be forgotten when comparing these wide divergences, that
each theory has been the result of experimental evidence, in what was,
at the time, and remains up to the present, a new and progressive
branch of science.
They agree that the spectrum colours are purer than the pigmentary
colours, and that by reason of their being referable to wave length
positions, they are most adaptable as standards of colour. There has
also been common agreement that certain colours are primaries, and
that all other colours are mixtures of these, but there has been wide
divergence as to their number and even the colours themselves.
[Illustration: PLATE I ILLUSTRATING THE POSITION OF THE PRIMARIES IN
RELATION TO THE COLOURS REQUIRED TO BE PRODUCED BY THE THEORETICAL
MIXTURES AND ALSO IN RELATION TO THE CHROMATIC CIRCLE.
A SEVEN RAY THEORY. NEWTON.
A SIX RAY THEORY. WERNER.
A FIVE RAY THEORY. NEWTON (_Early_). HELMHOLTZ (_Early_).
A FOUR RAY THEORY. HERING.
A THREE RAY THEORY. CHEVREUL. BREWSTER. HAY. REDGRAVE. FIELD.
A THREE RAY THEORY. YOUNG-HELMHOLTZ.
_To face page 4._] [_Lovibond, Colour Theories._
]