There is an urban legend that attributes the irregularities in the glass decorated by the Gothic cathedrals to the fact that Glass is not a solid but an extremely viscous liquid that, over time ends up falling dragged by gravity.
Well, according to experts, this story is a myth. And at the same time it really has a lot. Yes, it is complicated.
As we learned at school, matter can occur in three states: solid, liquid and gaseous. Then we would learn that the panorama is a bit more complex, with somewhat more unusual phases such as plasma, or the existence of a “triple point”, a combination of temperature and pressure under which matter can be in three phases at the same time.
In an article in The CovnersationPaddy Royall, a professor at the University of Bristol, explained a few years ago some details of this mystery and why the history of the windows of the cathedrals has some foundation Despite not describing a real cause of cause effect: the irregularities in these windows are due to the technique and not over time.
For Royall, the key to the matter is in the transition. To understand where glass fits in all this we can think of water or, more specifically, what happens when the water changes its liquid phase to its solid phase. When the water freezes it does so more or less sudden.
Small crystals arise from the liquid water, that is, regions where H2O molecules are structured in an orderly and invariable way. This crystallization occurs quickly, as a kind of infection that extends until the whole solidifies.
In any case, the water will become ice in a discreet and not continuous process: it will pass from solid fluid without further proceduresso that their molecules will go from disorder to order. The problem is that not all matter seems to behave with that immediacy. And the glass, or rather, the glass are the best example of it.
“The problem with the materials that form glass (which include plastics, alloys and ceramics, in addition to the daily ‘glass’) is that there is no obvious transformation. When cooling we cannot say the moment in which the glass becomes solid, ”Royall explains in his article.
And this is not simply due to a matter of temperature but in the same viscosity. So that a material crystallizes its atoms must “order” and structure. As explained to Livescience John Parker, from the University of Sheffield, “(the glass) cools quickly, but as it is so viscous, Atoms cannot be moved in a simple way to regroup in a more orderly solid structure, and are trapped in disorderly formations. ”
“(Glass) is by mechanically solid, but with a messy structure like that of a liquid,” adds Parker.
Something similar explains Royall in his article in The Conversation. “The reason that (the transformation) is difficult to observe is that to do so we would have to wait an extraordinarily long time (much more than centuries),” he says. However, the teacher gives us some details of how atoms and molecules are structured in this solid that is not such.
He explains that, if we look with a microscope, we can see how small groups of a few tens of molecules act differently: some are structured in orderly, as in a solid, while those around them remain unstructured, as in a liquid .
A difficult experiment
In 1927, the one that is considered “the slowest experiment in history was launched.” It is about Brea drop experimentan essay whose objective was to demonstrate that this substance was a liquid of enormous viscosity.
Those responsible for the experiment placed an amount of break in a funnel, all protected in a glass bell. Under the funnel, another container to collect the fallen break. After three years letting the break, those responsible for the experiment opened their mouths and left the gravity to do their job. Ten years later the first drop fell.
In the 95 years since the opening of the funnel, a total of nine drops of break to the second container have fallen.
This experiment remains active as curiosity and because it can still teach us things. For example, how environmental conditions alter the viscosity of this type of liquids. After the seventh drop (fallen in 1988), the University of Queensland installed air conditioning in the faculty that houses the experiment. The result: a remarkable slowdown of the speed at which the drops fall, that is, an increase in the viscosity of this fluid.
So, glass is a liquid, right? The question remains without a definitive answer. In the words of John Mauro collected by Livescienceglass “is neither a true liquid nor a true solid: it has properties of both but has its own state of matter.” “The technical definition It is that glass is a state of non-echinibrated and non-cristaline matter that appears to be solid in the short temporary scale but that relaxes towards the liquid state, ”added Mauro, expert in material science of the Penn State University.
The question of the time scale is important. The stained glass windows of the Gothic cathedrals are centuries behind. The temporal scale in which glass is located is much larger. That is why we know that, although there is something true in the legend of these stained glass windows, it would actually need more time so that we could observe changes in the structure of these materials. Much longer.
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Imagen | Antoine Pouligny / Jamieson Gordon
