Architects memo no. 109: November 2012
another reprise – colour durability
When it was suggested that I tackle the above subject, my
knee jerk, plaintive reply was “but I have already covered
that subject”. When the archivist advised me that was back
in 1984, I agreed that the boss had a point!
Architecture is a strange amalgam of art and practicality
and the role of paint in architecture aptly reflects this
dichotomy. Colour schemes play a major part in the area of
aesthetics and consequently, the ability for paints to retain
colour ‘fastness’ can determine the longevity of the original,
Colour in paints is provided by pigments (we will include
black and white, even though they are not strictly colours)
of which, in this highly technological world, there are literally
hundreds. It is the ability of all these various chemistries
to interact with light, absorbing some wavelengths and
reflecting others, that produces the phenomenon of colour.
Drilling deeper into the chemistry of pigments, it is found
that only specific ‘linkages’ in their molecules are involved
in this interaction, which gives each of these pigments its
characteristic shade. These groups are called chromophores.
As long as the chromophore remains intact, the colour stays
true – if it becomes damaged, the colour loses its integrity.
The major aggressors are chemical (including atmosphere
chemicals such as oxygen, and, in thermal areas, hydrogen
sulphide) and physical (primarily U.V. and visible light).
The most stable of chromophores are produced by metal
oxides, especially chromium III (green) and iron (red and
yellow ochres). These pigments are almost impregnable
even though they are sometimes accused of ‘fading’. The full
‘richness’ of any coloured pigment is only achieved when
it is fully encapsulated in a binding resin. In an exposed
paint, this resin layer will slowly erode away, leaving some
unbound pigment on the surface. In this unbound state, the
pigment loses some of its perceived ‘richness’ and appears
to have faded. The fact that it hasn’t can be shown by the
observation that the original colour can be ‘restored’ when
wetted with water. This, indeed, is a good test to see whether
any suspected ‘fading’ is truly fading or simply film erosion.
There are virtually no technical or commercial draw backs
with the above pigments – the only issue is a very limited
Stepping a little down from these ‘bullet proof’ pigments (in
which can be included oxides of titanium (white) and carbon
(black)) are a range of sophisticated, durable and expensive materials called ‘mixed metal oxides’ which typically involves
‘doping’ titanium, chromium, cobalt, or iron oxides crystals
with other exotic metal atoms. While these extend the
existing colour range (at quite a price penalty) it still remains
The dramatic expansion of colour shades came with the
discovery of organic dyes and pigments; starting with Perkins
Mauve in 1856 and followed by a veritable explosion of
colour technology around the turn of the 20th century, which
subsequently provided the basis of the modern chemical
industry. The most efficient, innovative and feared chemical
company the world has seen was called I.G Farben which
is one of the conglomerates that underpinned the scientific
and industrial efforts of Hitler’s Third Reich. I.G (Interessen-
Gemeinschaft) Farben literally means “those with a common
interest in colour”.
The organic chemical industry developed many new
chromophores that produced a hitherto unknown range of
brilliant colours. The stability of these new chromophores
was not always great (some were reported as fading in a
full moon) and the thrust of the pigment industry has been
to find more and more stable chromophores or to build
protective, umbrella groups around less stable chromophores
to improve their stability.
The commercial reality today is that there is available a wide
range of pigments with an equally wide range of price and
quality. Take the BS5252 colour 04E53. There would be at
least 20 different ways of formulating this colour, which,
judged from the initial hue, would be indistinguishable from
each other. The quality of the pigments used only becomes
evident with time. A poor pigment selection would see
dramatic colour change within two years; the Resene colour
used on the façade of the School of Architecture building in
Wellington is still (relatively) true to colour after 18 years.
All pigments are classified by international colour standard
testing for light and weather fastness and Resene is happy to
supply this data on each of the pigments used in their colour
system, on request.
Looking back over this memo (on my second G&T), I realise
that it has barely skimmed the surface of a tricky subject –
please come back to us if we can usefully expand.
Download as a pdf. (You will need Acrobat Reader).