Name (also legs, little legs, windows, tears) for the liquid formations on the inner wall of a wine glass, which can form with the circular pivoting of the glass (can). By pivoting creates a more or less high, vertically arranged liquid film (wine). At the top, the film begins to thicken and contracts into viscous, tear-like drops. These then flow back down to the liquid level. Decisive for the phenomenon with the wine is the mixture of water and alcohol but would work for any other mixture of two liquids with different boiling points. With pure water or pure alcohol alone it would therefore not occur. The tears and stained glass windows are visible in the shadow on the right (see arrow).
Liquids are held together by the attraction of their molecules, the so-called adhesion. The alcohol type ethanol at 78 ° C has a much lower boiling point than water. If parts of the alcohol evaporate, the surface tension of the film is changed, the remaining liquid contracts and flows down in the form of more or less large drops. The downflowing drops form windows. Depending on whether the distances between these tears are narrow or wide, can on the alcohol content getting closed. The smaller the distances between the tears (in the "pointed bow style"), the more viscous (thicker) is the wine and higher the alcohol content. The further the distances are (in the "round arch style"), the lower the proportion.
The effect occurs increasingly from an alcohol content of at least 12% vol. Sometimes it is claimed that the stained glass windows are also high in content glycerin point out. However, this is not correct, because glycerin has a much higher boiling point than water at 290 ° C. It is almost exclusively the alcohol content crucial. There are alcohol measuring devices that use this effect. These consist of a glass capillary with attached funnel and a measuring scale. At the top, a little wine is poured, which flows out again below. The adhesion leaves some wine in the capillary, which does not flow out. The alcohol content can then be determined from the height and the temperature by means of a table. The procedure is accurate to 0.5%.
Already in 1855, the British physicist James Thomson alias Lord Kelvin (1824-1907) recognized this phenomenon, which he called "tears of a strong wine". The discovery is often mistakenly attributed to the Italian physicist Matteo Marangoni (1840-1925), who published it in 1871 and is therefore also called Marangoni convection. See also below wine address. wine review and Weingenuss,