New approaches for the preservation of outdoor public murals: The assessment of protective coatings for mural paintings and painted architectural surfaces.

摘要

This doctoral research focused on the history, methods, and materials of public murals and their preservation. Over 350 public art programs exist in the United States, many of which have outdoor murals in their collections. The contemporary public mural movement began in 1969 and by 2012 there are thousands of murals located throughout the United States. Major mural programs are hosted in Los Angeles, New York, Philadelphia, and San Francisco, with emerging programs being developed in other cities. Mural programs, projects, materials, and preservation efforts between 2008-2011 were surveyed. Constant outdoor exposure (e.g. solar radiation, extreme temperatures and humidity, freeze/thaw cycling) of the unprotected acrylic mural paintings has resulted in fading, chalking, hazing, flaking, spalling, or yellowing of the mural paint system.;The current trends in conservation of outdoor public murals were also investigated. Treatment options included complete overpainting for image renewal, resaturation of images using varnishes and selective inpainting or toning, and resaturation of images using varnish only. The treatment selected by mural caretakers was based on a variety of factors, which often included: cost, accessibility, expected longevity after treatment, and sufficient photodocumentation of the original mural image.;The use of ultraviolet (UV) light stabilizing coatings was investigated for potential end-use on outdoor public murals. Ultraviolet absorbers (UVAs) and hindered amine light stabilizers (HALS) can work synergistically to prevent photodegradation. UVAs preferentially absorb UV, reducing potential radical production. HALS quench radicals and prevent photo-oxidation from advancing. UVAs Tinuvin 99, Tinuvin 400, and Tinuvin 477 and HALS Tinuvin 123 (BASF) were added (1-5% weight solids each) to waterborne Avalure AC 315 acrylic copolymer. The coating formulations were naturally (12 months) and artificially aged (1500 hours) and analyzed for the formation of degradation products using GC-MS, FTIR. The UV-protection range was measured using UV-Vis spectroscopy. The usefulness of UVLS-treatments on acrylic mural paints (Golden Artist Colors Heavy Bodied Acrylics) was assessed visually and using colorimetry.;Recommended concentration of UVLS for end-use in outdoor mural coatings are: at least 3% HALS and 3% UVA. Combinations of Tinuvin 123 and 477 performed best in both artificial and natural aging trials. Use of UV-protective coatings in addition to wall preparation, better materials, community education, maintenance programs, can extend the life of these important examples of our distinctive and irreplaceable social, artistic, and political heritage from the past half-century.