Laser Cleaning of Stone-QiangYuan Laser-Focus on laser cleaning

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Laser Cleaning of Stone

Jul 17,2026

On the streets, you'll see gargoyles, cornices, and fringes carved into stone, their intricate details obscured by a thick layer of crusty grime. Restoring old buildings is a challenging task, not just about removing surface grime, but about preserving the stone's natural luster while removing the "sulfate layer" or "black crust." Laser cleaning technology is like a precise surgery; it carefully removes harmful substances without damaging the stones—a process known as selective ablation.

The Working Principle of Laser Stone Cleaning

1. Selective Absorption and Reflection
Dark-colored contaminant layers absorb light, while light-colored stone substrates reflect it. The significant difference in their absorption thresholds for laser energy is the physical premise of "selective ablation."

Surface Black Shell: Black/dark gray sulfate dirt has an extremely high photon absorption rate, trapping the vast majority of laser energy.

Underlying Stone: Marble, limestone, and sandstone are mostly off-white, light yellow, or light brown, with strong reflectivity, absorbing only a very small amount of light energy.

Operators control the laser wavelength and energy density, keeping the energy range between the dirt's ablation threshold and the stone's damage threshold. All the light energy acts on the crust, while the original stone substrate retains almost no heat and remains undamaged.

2. Plasma Expansion and Stripping under Nanosecond Pulses

The equipment outputs nanosecond-level ultrashort laser pulses, and the energy is applied to the black shell instantaneously. The entire thermal action time is extremely short, and the heat does not have time to conduct and penetrate into the interior of the stone below. This avoids irreversible damage such as discoloration, powdering, and micro-cracks in the original stone from the source, and completely preserves the original texture and carving details of the stone.

Laser cleaning vs. traditional cleaning

Restoration Criteria	Pulsed Laser Cleaning	Chemical Cleaning	Steam / Water Jet Cleaning
Material Loss	Zero (Self-limiting removal)	High (Surface etching)	Low (Risk of cracking)
Chemical Residues	Non-destructive	Potential weathering effects	None
Platform Precision	High (Preserves fine details)	Low (Uniform spraying)	Medium
Ecological Impact	No water waste / chemical waste	Toxic runoff	Significant water resource consumption