Expert Guide: Perfect Stone Polishing Methods

Stone polishing is a meticulous process that involves refining the surface of the stone to achieve a lustrous and reflective effect. This is an important step in the manufacturing of stone products such as countertops, flooring, and decorative items. Understanding the techniques and principles behind stone polishing is crucial to achieving perfect results. It is usually accomplished using mechanical equipment and can be performed by both dry and wet methods.

• Dry polishing: This method uses polishing stones on the stone surface and uses mechanical equipment to operate quickly. Dry polishing is suitable for certain types of stone and provides a high gloss finish.

• Wet Polishing: This method involves using water as a lubricant during the polishing process. Wet polishing helps control dust and heat generated during the polishing process and is especially effective for heat-sensitive gemstones.

Stone polishing principle 

The art of stone polishing is governed by particle grinding and physical and chemical principles.

Principle of particle grinding: The process of particle grinding involves the transformation of abrasive particles from rough grinding to fine grinding and polishing. As the particles refine the stone surface, the wear marks grow from coarse to fine and eventually become invisible to the naked eye.

The various stages of particle grinding include:

1. Rough grinding: This initial stage requires grinding tools with deep cutting depths and high grinding efficiency. The purpose is to eliminate saw blade marks and enhance the smoothness of the stone surface.

2. Semi-finish grinding: Here, the marks of rough grinding are removed and new, finer lines are formed, resulting in a smooth and consistent surface.

3. Fine grinding: At this stage, the stone's patterns, particles, and colors appear clearly, the surface presents a delicate and smooth texture, and a light luster begins to appear.

4. Further fine grinding: As grinding continues, the surface of the processed stone becomes smoother, with a glossiness between 40 and 50 degrees.

5. Polishing: The final stage produces a mirror-bright and shiny surface with a mirror gloss of over 85 degrees.

Physical and chemical principles:

The physical and chemical principles of stone polishing cover the complex interaction between the polishing process, stone properties, and the effects of temperature and humidity. Dry polishing and wet polishing are the two main methods of stone polishing, each method has a different impact on the stone surface:

• Dry polishing: Using a polishing stone during dry polishing will cause the surface temperature of the stone to rise. As the temperature increases, the water in the grindstone evaporates, thereby increasing the concentration of the polished grindstone and creating a strengthening effect. This process helps improve the gloss of the product, with the ideal gloss reaching 85 degrees or higher.

• Wet polishing: After dry polishing, when the polished product becomes hot to the touch, a certain amount of water is added to the surface of the stone to provide a cooling effect. Care must be taken when adding water to avoid continuous or excessive addition, as too much water can hinder the polishing process and make it ineffective. In addition, excessive heat that occurs during dry polishing should be controlled to prevent burns and cracks on the stone surface.

It is worth noting that some stones, such as Shanxi black, black gold sand, Jining black, etc., may not reach the ideal 40-50 degree gloss after fine grinding. In these cases, traditional particle grinding principles alone may not be sufficient to explain the limitations. Instead, these stones require a delicate polishing process involving physical and chemical reactions affected by "dry and wet" polishing, as well as temperature fluctuations and subsequent cooling effects. After a combination of wet and dry polishing, the luster of these stones gradually increases, exceeding the 85-degree threshold. This highlights the complexity of stone polishing, where multiple factors including physical, chemical, and environmental factors come together to achieve the desired polish.

What affects the stone polishing process?

The process of stone polishing involves a combination of acquired external factors (such as the polishing technique used) as well as the inherent internal properties of the stone itself. While external factors are crucial in achieving the desired polish, it is equally important to consider the inherent properties of the stone when going through the polishing process. When looking at the external factors that influence stone polishing, several key factors come into play: the type of polishing agent, the polishing liquid or paste, the grinding tools used, the polishing pad, and the various polishing process parameters.

1. Types of polishing agents: The type of polish used is a key factor in polishing efficiency and quality. While some low-hardness micronized materials can be used as polishes, high-hardness polishes are usually preferred due to their wider application and superior performance. Especially diamond polishing powder can achieve satisfactory polishing effects on a variety of stone materials.

2. Polishing liquid (paste): Polishing fluid, often using water as the medium, plays many roles in the polishing process. It not only acts as a coolant for grinding but also promotes physical and chemical effects during the polishing process. If mechanical abrasion (e.g. using diamond powder) is the primary method of polishing, oil-based organic liquids (e.g. sewing machine oil) are preferred for their excellent cooling, lubricating, and dispersing properties. Diamond abrasive pastes are available in water-based and oil-based varieties and can also be customized using colorants. The formula typically contains a combination of abrasives, dispersants, carriers, water, and colorants, providing versatility and flexibility in the polishing process.

3. Polishing pads (tools, grinding blocks): The choice of polishing disc or polishing block is critical to achieving the desired finish on your stone surface. The hardness, wear resistance, adsorption, and elasticity of the polishing disc affect its suitability for polishing different types of stone surfaces. For example, the flexible polishing pad is great for polishing curved surfaces, while medium hard disk polishing is better for polishing flat stones.

4. Polishing process parameters: The parameters that control the polishing process, including the concentration and supply volume of the polishing agent, as well as the pressure and linear speed during the polishing process, have a significant impact on the polishing effect. Optimum concentration and supply of polish are critical to maximizing polishing speed, both under- and over-concentration can lead to reduced efficiency. Properly adjusting the pressure during polishing can increase the polishing speed, but excessive pressure may intensify the grinding effect and destroy the formation of a glossy surface. In addition, careful control of the rotational speed and linear speed of the polishing disc is crucial to prevent polishing agent waste.