Track 4: This New World: Preservation technology and emerging issues within our historic buildings and built landscapes
2 - Good Clean Fun: An Evaluation of the Effect of Various Laser Pulse Durations on the Surface Cleaning of Historic Architectural Terra Cotta
Tuesday, September 25
10:30 AM - 12:00 PM
Laser cleaning technology continues to rapidly evolve allowing for increased use of laser cleaning in architectural preservation. Concurrently, environmental concerns, regulation, and restriction of many chemical and micro-abrasive architectural cleaning systems are increasing. Other factors, including the necessary protection of adjacent building materials, and the relatively narrow range of acceptable working temperatures and environmental conditions further limit and complicate the use of many chemical and micro-abrasive systems. Additionally, chemical systems and some micro-abrasive systems are used with water which may enter to the interior of a building through a compromised facade and contribute to the distress of interior finishes. The use of water and chemicals may also introduce harmful salts into the surfaces being cleaned. All of these concerns indicate a likely future shift away from chemical and micro-abrasive cleaning methods where feasible.
Modern laser systems offer control of many variables to optimize the cleaning process and achieve the desired visual results. Laser parameters such as wavelength, pulse duration, pulse energy, pulse frequency, scan speed, fluence, and spot size can be tuned to achieve a range of results. Although several studies have been published reviewing the effect of 1064nm wavelength laser cleaning on stone surfaces, fewer studies exist for the laser cleaning of other exterior architectural materials. This study characterizes the soiling and substrate of terra cotta samples with a vitrified (glossy) white colored glazed surface which were removed from historic buildings. The samples were spot cleaned at different fluence levels with pulse durations ranging from 10 to 400 nanoseconds. Additionally, areas were cleaned in both damp and dry conditions to evaluate the effect of water-laser interactions and the potential benefit of laser induced micro-steam cleaning in removing soiling present on the surface and in recesses of the crazed glazing.
Each sample was documented with photographs and photomicrographs prior to and after cleaning. The cleaned surfaces were visually evaluated relative to uncleaned surfaces and the interface of cleaned area relative to uncleaned area was also evaluated in 2D and 3D using a Hirox 3D digital microscope. The gloss of the cleaned surface was evaluated under magnification with various light conditions. Once successful trials were completed, larger scale trials were performed on-site to evaluate the schedule and cost efficiency of the laser system relative to typical chemical and micro-abrasive systems.
- Upon completion particpantswill be able to review the background of the use of lasers for architectural cleaning
- Upon completion particpantswill be able to understand the variable parameters of the lasers used for testing
- Upon completion particpantswill be able to discuss the effects of the laser settings on the terra cotta soiling and substrate
- Upon completion particpantswill be able to review how laser cleaning lab trials translate to on-site trials and mock-ups