Why do Marble Sculpting still rust?

Marble Sculpting is currently a popular type of stone carving. Many people think that Marble Sculpting generally do not rust. In fact, this is not the case. The stone sculpture in many city squares and gardens appear to be raw embroidery. Let us analyze why Marble Sculpting in Marble Sculpting will rust. When dark brown rust (spots) appeared on the surface of the marble engraving tube, we were very surprised: we felt that "the marble engraving does not rust, and the rust is not the marble engraving plate, but may be a problem with the steel." In fact, this is actually a one-sided wrong view based on the lack of understanding of Marble Sculpting boards. Marble carved panels will rust under certain conditions.

Marble Sculpting materials have the ability to resist air oxidation, that is, they do not rust, and they also have the ability to corrode in acid, alkali, and salt substances, that is, corrosion resistance. However, its corrosion resistance level varies with its chemical composition, interaction, scope of application and type of natural environmental media.
Marble engraving is a relatively stable chromium-rich oxide film (protective film) formed on its surface to prevent the continuous penetration of oxygen molecules and re-oxidation to obtain rust resistance. Once this plastic film is continuously damaged for various reasons, the oxygen molecules in the gas or liquid will continue to penetrate or the iron atoms in the alloy will continue to separate, establishing loose compounds, and the metal surface may continue to rust. There are many ways to damage this protective film, including the following in daily life:
1. There are attachments of smoke or orc metal particles rich in other chemical elements on the metal surface. In a humid environment, the condensed water between the accessory and the Marble Sculpting board connects the two into a micro-battery, causing electrochemical corrosion and damaging the protective film, which is called an electrochemical reaction.
2. Organic compound juice (such as vegetables, noodle soup, phlegm, etc.) adheres to the metal surface and forms organic matter under the premise of oxygen injection. Citric acid corrodes the metal surface for a long time.
3. Acid, alkali, and salt substances adhere to the metal surface (such as edible alkali and lime slurry splashing on the decorative wall), causing local corrosion.
4. In the air polluted by the environment (such as sulfate, carbon dioxide, elegant sulfur oxide), when encountering condensed water, hydrochloric acid, sodium cyanide, and acetic acid points will be generated, causing corrosion.
It is precisely because of the above reasons that the living environment of Marble Sculpting is mostly outdoor. The natural environment is complex and the electrochemical reaction is aggravated. Therefore, after a period of exhibition, many marble sculptures require anti-rust coating on the marble sculptures by the person in charge.