Architects memo no.
9: May 1981
Colorwood stain - its development and uses
Staining is an art whose origins stretch back into antiquity;
the woad of the ancient Britains (also used by the Chinese) is one of
the earliest stains recorded. Dyes were obtained from variety of natural
sources: cochineal from insects, Tyrian purle from Mediterranean molluscs,
plus a wide variety of fruits, berries, dyewoods, peats, lichens etc.
The dyes were dissolved in water, balsams, oils, and ferments to produce
the earliest stains.
By definition, stains are materials designed primarily to impart colour
effects to surfaces rather than to form a protective coating.
Modern stains flourished with the start of the synthetic dye industry
about the turn of the century. Today there are literally hundreds of
dyes to choose from, each belonging to one of four basic dye-based types:
The water-soluble dyes are probably the most lightfast but are very
difficult to apply uniformly and they raise the grain of timber badly.
- Oil soluble
Easy to apply but tend to have very poor lightfastness.
- Spirit soluble
These have fair lightfastness but are very rapid drying. Great skill
is needed to apply them to large areas.
- N.G.R. stains
This class of stain attempts to combine all the good properties of
the preceding three. They achieve fair lightfastness, have slight
grain-raising and reasonable ease of application. Considerable skill
is still needed, however, to achieve uniformity over large areas.
It has, of course, long been recognised that pigments (as against
dyes) have excellent lightfastness. But, because they are opaque, pigments
have not been used much in transparent stains.
Some time ago, one of the problems of the paint industry has been
the difficulty in making lead-free bright reds, oranges and yellows
with good obliteration properties. The reason for this is that readily
available organic pigments tend to be transparent in oil-based media.
This can be explained technically by referring to the refractive index
"When a solid is immersed in a liquid of the same refractive index,
the solid seems to disappear (i.e. like putting glass into water). This
is the case when solids (organic reds and yellows) are mixed with liquid
The technical staff at Resene concluded that these phenomena
could be harnessed to produce a new and exciting kind of wood stain.
The result - Resene Colorwood: a range of colours possessing excellent
lightfastness while maintaining complete transparency. Other benefits
are controlled penetration and a medium-slow evaporation rate that makes
application virtually foolproof on all but highly porous surfaces.
Resene Colorwood colours are concentrated. Paler shades are achieved
by dilution with specially formulated Resene Colorwood Reducing Base.
Other colours can also be created by intermixing any of the Resene Colorwood
range. Grain highlights result from the natural differences in porosity
between spring and summer bands of wood. The more porous areas absorb
more stain to create deeper tones. For maximum highlighting effect,
excess Resene Colorwood should be wiped off the hard grain with an absorbent
Application by brush is the normal method of applying Resene Colorwood.
But porous materials, such as chipboard or cork, can draw Resene Colorwood
from the brush and create dark spots. Here, use of a pad is recommended
to achieve perfect uniformity.
Properly applied, Resene Colorwood will dry in eight hours. Excessive
application in an attempt to increase colour density only prolongs drying.
Correct colour strength is best achieved by using the right shade rather
than heavy coats of a lighter one.
Resene Colorwood has been successfully applied to all common timbers,
particle boards, cork, cane, hessian and ropework.
For protection Resene Colorwood can be overcoated, but not with average
varnishes and urethanes. These tend to 'yellow'to the detriment of the
vivid Resene Colorwood colour beneath. Resene has produced a special
range of polyurethane finishes with minimum yellowing characteristic.
It consists of Resene Poly-Gloss, Resene Poly-Satin and Resene Poly-Flat
- the latter possessing excellent grain filling properties and, as such,
is recommended as a first coat whatever final finish is required.
In 1995 Resene launched Resene Aquaclear, a waterborne alternative
to turps - thinned oil-modified varnish. Resene Aquaclear can be washed
up in water and gives off low odour on application. In only a few years,
Resene Colorwood has almost completely replaced dye-based stains in
the architectural market. Its success has been due to its ready acceptance
by architects, specifying authorities and painters alike. While for
the home handyman Resene Colorwood has opened-up all sorts of exciting
Refer to Data Sheets D50A,
for further information.
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