It is the filling that warms the glass.When gold is deposited onto a surface at random, it first forms miniature islands.Since these are not connected to each other, the result is an insulator.Then, as more gold is added, bridges form between the islands.At a certain point these bridges transform the developing network from an insulator into a conductor, by letting electrons hop from island to island.That permits heat to spread.The network will now, like any other metal, absorb heat if left in the sunshine.It does so best, Mr. Hachler and Dr. Poulikakos say, when it reaches the so-called percolation limit - the moment at which it switches from an archipelago to an electrically interconnected sheet.The titanium-dioxide layers boost that absorption.This substance has a high refractive index, meaning the speed of light passing through it is greatly reduced.That prolongs the time such light can interact with (and thus heat up) the gold.The upper layer of titanium dioxide also protects the gold beneath it from damage.Glass coated with Mr. Hachler’s and Dr. Poulikakos’s invention is, they claim, four times more effective at preventing fog than an uncoated surface.
