Decorative Arts and Sculpture—Outdoor Sculpture Coatings

Decorative Arts and Sculpture | Featured Project | Outdoor Sculpture Coatings Research

Since the J. Paul Getty Museum acquired an outdoor sculpture collection from the Fran and Ray Stark Revocable Trust in 2006, the care of the collection became the responsibility of the Museum's Sculpture and Decorative Arts Department. The department entered a new field of study, initiating research into the materials, techniques and conservation of outdoor sculpture and we had the opportunity to engage with the living artists. Of the 28 works, most are made from cast bronze and lead, but there are also fabrications out of stainless steel, painted metal, and ceramic. One area of research involves the performance evaluation of protective coatings including cold wax and clear lacquers.

Wax is one of the most common materials used in the maintenance of outdoor bronze sculpture and has been incorporated into our yearly maintenance plan over the years. Proprietary paste waxes were initially applied cold over pre- existing Incralac—a commercial acrylic clear lacquer. Since it was commonly used by conservators in the United States, Butcher’s paste wax was adopted. However, either it was a bad batch or the formula changed: we noted a decrease in Conservators work on Horse (Gift of Fran and Ray Stark. © performance. One of the challenges in using a proprietary Estate of Elisabeth Frink. 2005.106.1) product is their trade secret becomes our blindness to changes that may impact our application. A preferred lab-made wax blend was developed—based on recipes from the National Park Service—by modifying the melting point, substituting solvents, and changing the blended components to suit a hot California climate.

In the United States, the National Park Service (NPS) has been on the forefront of customizing wax blends for use in conservation. In a memorandum published by the NPS in 1967, the finish on Theodore Roosevelt’s statue in the District of Columbia by Paul Manship was given detailed waxing instruction to the artist from an Italian bronze-caster/conservator named Bruno Bearzi to use beeswax in turpentine twice yearly. A decade later, the same statue was restored and waxed in a similar manner using a homemade blend of microcrystalline waxes and Cosmoloid 80H provided by Steven Tatti, a private conservator in New York City. Built upon Tatti's blending, the NPS Cultural Resources Management Specialist, Nicolas Veloz, adopted the recipe and added carnauba to impart hardness. In 1986, when conservator Arthur Beale published a study stating that natural waxes such as beeswax and carnauba did not hold up well in a polluted environment, Veloz was advised by the wax manufacturer Baker Hughes to use Petronauba C. (Veloz also switched to using Polywax 500 instead of Cosmoloid 80H later due to a temporary lack of availability in the 80H.) Since 2005, the NPS has recommended proprietary paste waxes such as Butcher’s or Trewax for the conservation of outdoor bronze.

Veloz provided the Getty with his formulation in 2006 as containing 71% Victory white or brown, 13% Polywax 2000, 13% Petronauba C, 3% Polywax 400, although he clearly modified his mixture over the years for reasons of availability, appearance, and durability. The Veloz-type wax was used that year at the Getty Museum, however the film seemed to be too soft for our California climate and the surface experienced a lot of smearing on hot summer days. The homemade Getty-Veloz wax replaces the Victory wax with Multiwax W-445 due to a period of its unavailability, and we harden the mixture by adding higher melting point microcrystalline waxes. Although polywaxes can also raise the melting point of blends, our concern over the study by conservator Dana Moffett indicating that polyethylene waxes become insoluble, led us to remove them from the blend. The

current recipe is as follows: 78g Be Square 195 Black, 12g Petronauba C, 5g Be Square 175 Black, 5g Cosmolloid 80 H, 200 ml Shellsol A100, 100 ml Shellsol D38.

In collaboration with the Getty Conservation Institute scientists, we have been comparing waxes for use in outdoor sculpture maintenance by examining working properties, solvent retention and uptake, solubility and removal, protection from corrosion, impact of melting point, and more. One method for comparing the corrosion protection of various wax mixtures involves image processing of naturally aged, waxed coupons that are scanned on a flatbed scanner. The technique provides stable and uniform illumination with the aid of a template and a Qpcard 202 color card with known CIE L*a*b* values. We designed a workspace using the Nip2 software - an interface of VASARI Image Processing Software, or VIPS. The Nip2 workspace automatically measured the color pixel-by-pixel for each bronze coupon and calculated the change in color of each pixel before, during and after aging using ΔE (CIE 2000) color difference formula. A final metric for the rate of color change (as a proxy for rate of corrosion) was then calculated in terms of ΔE. Preliminary results on brass coupons that were cold-waxed with a series of mixtures have shown that the proprietary waxes, such as Trewax and the BWC Butcher's bowling alley wax were good performers as well as BE SQUARE 185 amber microcrystalline wax. Our modified Veloz paste wax was slightly less effective, but the worst performers were polyethylene waxes.

An evaluation of cold paste wax used in conservation for outdoor bronze sculpture Cu 220 sheet metal, cold-waxed / Naturally aged in Los Angeles for 7 weeks

CONTROL Uncoated Butcher’s® Beeswax BeSquare 175 BeSquare 185 BeSquare 195 Bowling Alley Black Black Black (2006)

BWC Carnauba Clapham’s Cosmolloid Conservator’s Getty/Veloz Butcher’s® Beeswax 80H Wax Bowling Alley (2015)

Liberon Black Mohawks™ Multiwax® Paraffin Petronauba C Polywax® 500 Patinating Blue Label W-445 Wax

Polywax® 2000 Renaissance Sculpt Trewax Turtle Wax® “Veloz” Nouveau

The J. Paul Getty Museum Decorative Arts and Sculpture Conservation

Brushed, cold paste wax evaluations were conducted by applying waxes to brass coupons that were naturally aged. These coupons were scanned after aging and analyzed for color change.

In addition to waxes, the department has been researching clear lacquers because the bronzes were acquired with a pre-existing Incralac coating. Incralac was developed in the 1960s based on research initiated jointly by the International Copper Research Association (INCRA) – now the International Copper Association - and a cohort from the British Non-Ferrous Metals Research Association (BNFMRA). Both institutions determined that Acryloid B-44 manufactured by Rohm & Haas Co. – now Paraloid B-44 by Dow Chemical – gave superior protection for an air-drying coating on copper alloys and had good appearance and working properties. INCRA and BNFMRA developed formulations that contained 30 wt% B-44 in toluene and butyl acetate (or ethyl

alcohol), benzotriazole (BTA) as a corrosion inhibitor and either silicone fluid or epoxidized soya bean oil (ESBO) as a leveling agent.

Art conservators quickly adopted the coating for the protection of outdoor bronze sculpture and it remains a popular choice today. A substantial amount of research has been carried out on Incralac over the past 10-15 years through its inclusion in a number of aging and weathering studies. We published an article in JAIC on the history of Incralac and its use in conservation in 2017. The performance can vary depending on chemical patinas, solvent carriers and additives. The recipe was trademarked under the name Incralac, but it was never patented and manufacturers have been free to modify the formulation at will. In fact, environmental regulations have prompted changes in solvent in order to reduce the volatile organic compounds (VOCs) and the solvent-based coating will likely be replaced with a new water-based product line. It is already highly restricted in the state of California.

Application of a protective Incralac coating on an outdoor bronze sculpture at the Getty.

A review of the development of Incralac and modifications made over the past few decades was the springboard to designing an experiment on lab-made versions. Testing different formulations in the laboratory could provide another avenue for conservators and scientists to ascertain the effects of formulation changes. Preparing Incralac coatings in the laboratory could also provide more control in treatments and coating studies, and perhaps help to improve its performance on outdoor sculpture. Furthermore, exploring different solvents could lead to less toxic formulations that reduce health risks. One of our studies compared lab-made Incralac formulations with commercial Incralac (water and solvent-based) on naturally aged brass coupons. Permalac, another proprietary acrylic coating, was also included and has recently been adopted by some conservators as an alternative.

Nine coatings related to Incralac were evaluated by a multi-analytical approach to compare application, performance, appearance and reversibility. The study showed that a lab-made low toxicity Incralac using 1- Methoxy-2-propanol can provide protection on brass coupons similar to the commercial product. The performance of Permalac was similar to that of Incralac, whereas the water-based Incralac—developed in

conformance to environmental regulations—performs much worse. Deconstructing the formulation of Incralac by designing a series of imitation coatings with different additives revealed some trends but additionally exposed new questions that can be explored in the future; for example, comparing chemical change using GC- MS, performance on different substrates (chemical patinas), additional additives, longer aging and varying climates.

In general, some of the results from the study shows that BTA improves coating performance as seen by the difference in pitting corrosion, adhesion and electrochemical impedance values. BTA does appear to affect solubility, however, as the coating without the additive is much more reversible before and after aging. The ESBO plasticizers performed best and provided better scratch resistance, greater solubility after aging, and easier application. Matting agents appear to play an unexpected role in this study, as the matte Incralac and Permalac performed better by having the least corrosion, best electrochemical impedance values, and best appearance; however, the addition of the matting agent appears to reduce its solubility over time. Our initial findings were presented at the 18th triennial conference of ICOM-CC in Copenhagen. The department continues to re-evaluate the use of coatings in the Stark collection and hopes to pursue more research projects on new products, home-made lacquers and wax mixtures, and application techniques.

Contributors to This Research

J. Paul Getty Museum Getty Conservation Institute Additional Contributors

Julie Wolfe Michael Schilling Dr. Rosie Grayburn Dr. Arlen Heginbotham Herant Khanjian Formerly at GCI, now Associate Jessica Chasen Joy Mazurek Scientist and Lab Manager at Winterthur Museum, Garden & Library

Alan Phenix Formerly at GCI