Sandblasting and microblasting are abrasive processes used to create unique textures and visual effects. While these methods share similar principles, they differ in the size of the abrasives used and the level of refinement achieved. They are commonly applied to various components of a watch’s movement or external parts, providing a matte, satin, or granular finish.
Methods
Sandblasting
Sandblasting involves projecting an abrasive, often in the form of sand or beads, onto the surface of a component to create a rough or satin texture. This process is typically carried out using a compressed air gun, often within a sandblasting chamber to control impact and minimise the dispersion of abrasives. The pressure, angle of impact, and distance from the surface directly affect the depth and quality of the finish.
Microblasting
Microblasting, on the other hand, uses very small metallic or ceramic beads (usually between 20 and 100 microns in size), precisely calibrated and projected at high pressure onto the surface. Unlike sandblasting, microblasting produces a much finer, more homogeneous satin finish, making it ideal for subtle finishes. This technique is typically performed using specialised machines, such as compressed air microblasting cabinets, which allow precise control over the flow of abrasives.
Abrasives Used
The choice of abrasive plays a critical role in the final result of sandblasting and microblasting. It depends on the desired texture and the material of the component.
- Sandblasting:
- Traditionally, silica sand was used, but it has been increasingly replaced by modern, less abrasive materials like granite, corundum, or aluminium oxide. These abrasives produce a more uniform finish while preserving the metal surface more delicately.
- Microblasting:
- Glass beads are the most commonly used abrasive, providing a soft and satin finish. Other materials, such as stainless steel, ceramic, or even hardened plastic beads, may be used depending on the desired outcome.
- The abrasive’s size, hardness, and calibration significantly influence the final texture. For example, glass beads create a finer, more uniform texture, while harder abrasives like aluminium oxide leave a rougher, more granular surface, ideal for a rugged effect.
Tools and Machines
The equipment used for sandblasting and microblasting varies depending on the production scale and the complexity of the component to be decorated.
- Sandblasting Chamber: A basic setup for sandblasting, consisting of a closed chamber where the operator inserts the parts to be blasted. The chamber features a gun that projects the abrasive at high pressure.
- Microblasting Machine: Microblasting machines are often more sophisticated, with systems to regulate air pressure, temperature, and abrasive flow. These machines may be manual or automated, offering consistent and homogeneous results. Advanced models automatically control projection angle, pressure, and exposure duration based on the material and design of the component.
Components Suitable for Sandblasting or Microblasting
Many watch components can be decorated with sandblasting or microblasting. Common examples include:
- Bridges: Essential movement parts that benefit from a satin or granular finish, adding visual appeal and improving scratch resistance.
- Plates: Main movement plates can be microblasted for a uniform, aesthetic surface.
- Dials: Some dial surfaces are sandblasted or microblasted for a unique texture.
- Cases and Metal Bracelets: Elements such as case middles, bezels, case backs, pushers, and bracelet links can also be sandblasted or microblasted.
Effects and Finishes Achieved
- Matte or Satin Finish: Determined by the nature, calibration, and projection pressure of the abrasive.
- Unique Aesthetic: These finishes create subtle light reflections and intricate contrasts, lending an artisanal and refined look to both the movement and external components.
- Increased Durability: The processes slightly harden treated surfaces, offering enhanced protection against wear, corrosion, and scratches through work-hardening.
- Visual Contrast: Contrasting polished surfaces with sandblasted or microblasted areas on the same component can highlight movement details, creating a more complex and elegant appearance.
Influence of Abrasive
The abrasive has a significant impact on the desired texture and visual effect:
- Finer Abrasives: Such as glass beads in microblasting, produce a soft, smooth texture without visible asperities, ideal for a subtle and refined finish.
- Coarser Abrasives: Such as sand or aluminium oxide in sandblasting, create more pronounced textures, giving a rugged and robust effect, perfect for exposed components or industrial designs.
Precision and Care
These techniques require precise mastery to ensure an aesthetically pleasing finish that meets high industry standards while maintaining the artisanal spirit of the craft. Excessive pressure, incorrect projection angles, or prolonged exposure can distort the contours of a piece and dull sharp edges.
Sandblasting and microblasting are versatile techniques that balance modern technology with traditional craftsmanship, offering unique textures and finishes that elevate the beauty and durability of horological components.