b'the science behind cool coloursCool Colour technology is something Resene technical director Colin Gooch and his team have been researching and developing for some time. It has involved looking closely into New Zealands environmental factors and blending pigments to achieve the right balance of colourfastness and durability. We didnt want to restrict homeowners and architects from using dark colours. In doing so, though, we needed to come up with a way to protect substrates that were temperature sensitivea pigment that could be put into binders and made into a paint safe to use on most applications, says Colin.When looking at the role paint can play in temperature control in buildings, it comes down to colour, he says. The ability of white to reect visible light extends through into the infra-red and, because of this, white surfaces remain relatively cool to touch, even in direct sunlight. The opposite is true of black and dark colours, which absorb light in this infra-red area, resulting in signicant heat build-up in the surface. As the emissivity of paints is not particularly good, the surface heat is conducted into the substrate and then radiated into the building.However, Colin points out that not all dark colours behave in this way. In terms of technology, Mother Nature had the trick and beat us by a few million years. Most plants have leaves of a very high chroma greensome of them are very dark indeed. If those leaves reached the same temperature when exposed to solar radiation as those of a similarly coloured paint, they would shrivel and die. The fact they dont is because that pigmentchlorophyllabsorbs what it needs from the visible range to photosynthesise, but reects the infra-red range, keeping the plant cool.Over the past decades, there have been vigorous efforts to create heat-resistant pigments in the ceramics industry, as most tints break down at the very high temperatures under which ceramics are red. Novel ways were discovered of doping refractory metal oxides of titanium, zirconium, chromium, and so on, with other metal ions to produce a wide selection of high-temperature colours. More recently, the behaviour of these mixed oxides were examined under infra-red and the results showed an ability to withstand a range of very high temperatures. Focusing on this aspect, further renements were made to maximise this for use in various commercial applications.Using these ndings, Colin and his team took the very popular COLORSTEEL roong colour Karaka and incorporated into it these infra-red reecting pigments. Comparing the new blend against traditional coatings over a ve-minute standard Resene test revealed a whopping 12C degree drop in temperature.ReseneBlue Smoke This 12C degree difference can make a tremendous difference to the stresses Resene exerted on the substrate and can have a telling effect on its stability and heat Burnt Crimson gain, explains Colin. ReseneCloud Burst Since 2004, when it was initially launched in Resene Hi-Glo acrylic, Cool Colour Resene technology has been in hot demand. It has since been extended for use on a Dieselvariety of claddings, including aluminium, block and brickwork, concrete and ReseneHolly plaster, bre-cement, plywood, stucco and zincalume. | 47'