Marble is a type of stone that is a very versatile material and is used in various ways. It can be utilized in sculptures, and as a material for building houses.
A marble surface is a relatively smooth, glossy surface that allows light to pass through it. It can be a good material for sculptures because it is durable, easy to work with, and doesn’t absorb oils.
Marble can be polished to create a shiny surface without compromising its porous qualities. This makes it the perfect choice for sculpting compared to other materials.
Although there is no single formula for the best marble sculpt, there are a few tricks to get the most out of it. The process begins with a full-size model or a small maquette. Once the model has been carved, the next step is to use fine detail tools to create the desired shape.
A hammer and point works is one way to create a smooth, non-slip marble surface. This is a technique used since ancient Greek times. In modern day sculpting, the hammering process is often done manually or with the aid of automatic machines.
Many monuments are affected by biofilm. This form of bio deterioration is caused by phototrophic and cyanobacterial microorganisms, which secrete polyphenolic compounds. They can be damaging to the stone surface and lead to discoloration.
Biofilm is an extracellular polymeric substance, which facilitates attachment to the substrate and also protects the organism from degradation. It is usually composed of cells and is found on a variety of surfaces. Some microbial species can even mobilize and colonize marble, which can result in stone biodeterioration.
Marble sculptures are particularly vulnerable to microbial pigment discoloration. Microbial pigments are typically colorless or red, and can appear on a marble surface. In some cases, these pigments may not actually cause physical damage to the stone, but they can alter the appearance of the monument.
Candoglia marble is used in decorative elements of cornices, which are exposed to highly polluted urban air. These elements are therefore subject to intense surface erosion.
Marble is a metamorphic rock formed by recrystallization of dolomite or calcite. During metamorphism, marbles may be deformed, broken, or crushed. These stones can be shaped, polished, or even machined.
Marbles are composed of interlocking crystals of calcite. Often, the original bedding is evident in marble sculptures. This is a result of the directional thermal expansion of calcite crystals. However, a lack of strength makes marbles more prone to breaking.
Most marbles are made from a mixture of calcite and dolomite. The calcite is a calcium-magnesium carbonate. Its crystalline form is doubly refractive, meaning it transmits more light in one direction than in the other. As a result, marbles show rhombohedral cleavage.
In the past, marbles were not always pure calcite or dolomite. They often contained accessory minerals, such as feldspar, diopside, brucite, or spinel. Some of these minerals can be colorless, while others can be pale yellow, green, or brown.
Crystallographic preferred orientation
Marble is an architectural stone that has been used for monuments since antiquity. It displays complex biological, chemical, and thermal weathering phenomena. In particular, its structure shows a strong crystallographic preferred orientation.
Various studies have investigated the main characteristics of marbles and their degradation processes. Some of these include the effect of shape fabric, the crystallographic preferred orientation (SPO), and the random orientation distribution function (ODF).
The aforementioned SPO and ODF have significant impact on thermal and thermomechanical behavior of a stone. Furthermore, they can be combined to form transgranular microcracking.
A finite element approach was used to analyze and quantify the influence of various microstructural features on a marble’s propensity for microcracking. Microstructural standard deviations were determined as well as the average elastic strain energy density distribution. These were then analyzed in order to identify regions of propensity for microcracking.
Ultrasonic velocity distribution
Ultrasonic wave measurements are one of the most commonly used NDT methods in stone conservation. They are often used to detect damage and alteration below the surface. The results of these studies have been used to control conservation procedures, evaluate the effectiveness of treatments, and monitor the performance of treated materials.
A study was carried out on 25 Carrara marble sculptures. Two types of degradation crusts were identified by ultrasonic measurements. The ultrasonic indirect method was also used to determine the thickness of these degradation crusts. In addition, the distribution of salts was examined. Areas with higher concentration of salts were observed.
Ultrasonic tomography is a non-destructive technique that uses two probes to send acoustic pulses through an object. The position of the transducer and receiver determines the time it takes the P-wave to travel through the material. Using this information, the velocity can be calculated. Stone conservation is key for marble sculptures.