The view from the window seat of the jet bound for your next holiday should soon be even more spectacular. Scientists have discovered why aircraft windows acquire the cross-hatched pattern of scratches.
Research by a team of experts from the Australian science organisation CSIRO has discovered that the effect, dubbed "crazing", is principally caused by the movement of water inside the transparent plastic window material.
Not only can this ruin a passenger's view, but it can also impair the pilot's vision. So airlines regularly remove windows, polish the surfaces to remove the cracked layer and refit them.
Hans Griesser, who led the research, said: "These cracks, which look like scratches, don't pose any threat to safety, but they are a major expense for airlines."
The scientists found that as the aircraft's altitude increased, the reduced air pressure forced out air trapped in pores of the acrylic material used to make the windows.
The frequency of these changes, as the aircraft ascends and descends, causes stresses in the plastic that cannot dissipate evenly. This leads to the development of fine cracks.
The only solution so far has been for the airlines to polish the windows to remove the crazing, but each time the pane gets thinner.
Once the pane reaches such thinness that might compromise the integrity of the window, it has to be replaced.
But the CSIRO team has successfully trialled a process of coating the windows with a water-repellent polymer flexible enough to cope with changes in the shape of the window without coming unstuck or crazing.
Geoff Thomas from Australian firm Aeroclear, which has been working on the project with CSIRO, said the technique was only a partial solution, but that it made a difference.
"It is difficult to produce a transparent coating that completely eliminates water-vapour transport because water molecules are so small. However, we recognised that even slowing the transport would help reduce the crazing," he said.