The story now jumps to an event nearly forty years later, where I was again the object of suspicion.

I was standing on the platform of a suburban station in north Copenhagen when I noticed a poster in a glazed frame lit by the failing sun of a winter afternoon. The subject of the poster was crime: a dire and crudely expressed warning against copying CDs. What had caught my attention, however, was the pattern of condensation behind the glass. The close up, outlined in orange on the left, shows the close association of condensation with the white letters.

Figure 2. The condensation behind the glass covering a poster is concentrated over the white parts of the image.

It is not only a crime to copy a CD, it is forbidden to photograph the property of the Danish State Railways. A railway employee came rushing along the platform, waving the brush he had been using to sweep the same and explained the seriousness of my action. Fortunately the train was just pulling into the station. I waited for the warning tralala and stepped smartly into the carriage as the doors slid together.

The shock to a timid middle class citizen on being accused of a crime while innocently observing the passing scene jerked my mind back to that long ago afternoon when I, for the only time in my life, sipped champagne with the Landed Class of England.

As I huddled down in the seat, preparing to pretend not to be there if the railway police boarded the carriage at the next station, I combined my two observations with my knowledge that many organic dystuffs have such an intense colouring power that they can be dusted sparsely onto the surface of glass as a dry powder which is almost invisible. When these tiny particles come into contact with water they dissolve to give an intense stain. Methylene blue, for example, is used in this way to detect pinhole defects in waterproof rubber enclosures.

Why is the condensation so closely tied to the pale areas of the pictures? It must be that the dark areas heat up more in the sunlight and some of this heat is released as long wavelength radiation which is absorbed by the glass. The pale areas absorb less light and also emit less long wave radiation. The reflected light passes unhindered through the glass. Therefore the glass will be cooler in front of the pale areas, so that will be the first place to suffer condensation. All this of course depends on there being some water present. That could easily be arranged by varnishing the painting with hydrophilic gelatin instead of the usual hydrophobic resin varnish. The shine is the same.

The deeper explanation for the blood flowing from the face in the portrait must be that my former colleague was jealous of losing the flute player to an insignificant person who played such a scarcely used orchestral instrument that during a forty bar rest I had rested the instrument on my knee, with such fateful consequences. The fact that he was also a fanatical opponent of blood sports hardly dulls my piquant thrill at being the object of a cunningly prepared crime of passion.



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