Covering a window with White Spain to keep the heat out sounds, put like that, like one of those social network tips good for every home and every season, when in reality it isn’t. The powdered calcium carbonate, which we call White of Spain (known in France as Blanc de Meudon because of the chalk quarries from which it was originally extracted, namely the city of Meudon, near Paris) really reflects a part of the solar radiation, but the advantage is only seen in very specific situations, which we will see in the next paragraph.
Where treatment can make sense
In these it can really be a good solution, especially in the presence of windows constantly exposed to the action of the sun’s rays:
Because on the window at home, usually, it is not needed
Outside these three contexts, utility drops significantly. Any window, already equipped with a shutter or blackout curtain, obtains the same result, or rather better, simply by remaining closed during the hottest hours, without the need to prepare a mixture and then remove it a month later with a sponge and water. Spanish White becomes a sensible option only where an adjustable darkening alternative is missing, specifically for greenhouses, skylights and shop windows.
How it applies, for those who fall into these cases
The powder dissolves in water until a fluid mixture is obtained. It is spread with a cloth or sponge in a thin layer, preferably on the external face of the glass and in the early hours of the morning, when the surface is still cool. To remove it, all you need is water and a soft sponge, and in the case of greenhouses it is often not even necessary to intervene, because the product comes off on its own with the arrival of the first rains.
