The researchers from St Petersburg University have studied 17 fountains of the Peterhof Fountains and discovered why dense grey-yellow colour crusts are formed on the surface of the monuments and bowls. The study is published in Environmental Earth Sciences, Springer.

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It is a matter of couple of months when the Peterhof Fountains is open again. It is an event that inspires, excites and engages both residents and guests of St Petersburg who visit Peterhof, a world’s capital of fountains. SPbU’s scientists in mineralogy and crystallography will preserve the beauty of the fountains as they revealed how we could inhibit the formation of dense grey-yellow colour crusts on the surface of marble, granite, gold, and even polyester resin.

During our experimental research in Peterhof, we discovered a rare water carbonate.

Candidate of Geology and Mineralogy, lecturer at SPbU Oleg Vereshchagin

“The mineral was described in saltmarshes, caves, and other exotic locations. Yet it has never been found on monuments or in fountains. Moreover, the crusts consisted of even rarer magnesium carbonates: lansfordite and nesquehonite”, — said the first author of the article, Candidate of Geology and Mineralogy, lecturer at SPbU Oleg Vereshchagin.

The results were quite astonishing as the marble monuments in St Petersburg that are located under the open sky are more likely to be covered by patina that is rich in clay plaster. The permanent rains and emissions containing sulfur make marble have blackened plaster crusts. Through the chemical reactions, the needle-like crystals of clay plaster come up through the surface of the monument, revealing crumbled marble beneath.

“Consequently, a nose or a finger may come off,  — said SPbU Professor, Doctor of Geology and Mineralogy Olga Frank-Kamenetskaia. — It is the most dangerous disease for the monuments in St Petersburg, although we can observe this situation in Europe as well, for example in Florence. Interestingly, if we compare two monuments that are made from one type of marble, of the same age and located in the same place, the more intricate the sculpture is, the more it is prone to destruction, unlike the monuments with simple forms, as water on them evaporates more quickly”.

The situation in Peterhof is different: SPbU, Peterhof State Museum Reserve, and Heritage Restoration Company studied the samples from 17 monuments. These samples did not contain any clay plaster crusts, rather calcite and a number of rare minerals. Then, the experts collected the samples of water for the fountains that is supplied by a gravity-fed water system and carried out the experiments. As a result, the scientists came to a conclusion that the cause of the formation of carbonate crusts on decorative fountains is the high content of carbonate ions in water.

“The bowls of the fountains are so-called chemical reservoirs as water moves in circles, gaining one components and losing others, — said Oleg Vereshchagin. — Interestingly, the carbonate minerals are formed due to a high pH level and high Mg ratio. Yet these conditions are not typical to Peterhof, as we revealed. Presumably, it is time that plays a role: temperature fluctuations create a necessary environment during summer. In a nutshell, now we have a clear picture of what minerals can be found in the Peterhof Fountains and we therefore can control the process and even inhibit it by reducing the water hardness”.

“The Peterhof sculptures are mostly made of the Italian Carrara marble that is one of the most iconic luxury Italian marbles in the world. Unfortunately, precipitations and fountain water make the marble have yellow build-ups. I am happy that we are collaborating with the SPbU’s scientists. As Nikolay Gumilev told, “And white marble was shining again. Alone, thoughtfully and proudly”, I want our marble be proud and shining. We therefore need new technologies and projects on preservation of the water-supply system that we have been developing for the last ten years”, — said Director General of the Peterhof State Museum Reserve Elena Kalnitskaia.

“What the SPBU’s scientists have been studying is vital for preparing the monument cleaning guides for the Peterhof monuments as it will help us develop specific methods and compositions to reduce the effect of lime-rich water from the Ropsha slopes. Yet we can fully remove the carbonates only during the complex restoration in the laboratories. Still the proper monument care can prevent the formation of the crusts”, — said the curator of the Sculpture Fund of the Peterhof Museum Reserve Natalia Khadeeva.