Winterthur/University of Delaware Program in Art Conservation's Mural Materials Research

Amanda Norbutus Blog: 10/10/08

Amanda Norbutus with paint samples*

Hi, I’m Amanda Norbutus, and I’ve just started my first year as part of the University of Delaware Preservation Studies Doctoral Program. I will be researching the current protective coatings available for exterior public murals, and then I will formulate and test a novel coating as part of my doctoral research. I recently received my M.S. degree in analytical chemistry from Villanova, following a bachelor’s in history and chemistry. Currently, I’m working with Dr. Joseph Weber from University of Delaware on the reading of 700+ samples of mural paints and coatings prepared by Jessica Keister and placed outdoors in Delaware on the grounds of the Winterthur Museum and Garden in 2005.[i] Five types of paints are being tested:

Manufacturer and Trade name	Paint Pigment Name[1]	Manufacturer’s Number
Golden Artist Heavy Body Acrylic Colors	Cobalt Blue	1140-4
	Hansa Yellow Opaque	1191-4
	Pyrrole Red	1277-4
	Titanium White	1380-4
NovaColors Artists Acrylic Paint	Ultramarine Blue	122
	Cadmium Yellow Light	123
	Cadmium Red Medium	125
	Titanium White	118
Sherwin-Williams’ Sher-Cryl HPA High Performance Acrylic	Blue	*The Sher-Cryl paint is not readily available and was given to mural artists as a gift.
	Yellow
	Red
	Valspar American Tradition Exterior 100% Acrylic Flat House Paint White	73340
Keim Mineral Paints Ltd Granital	Cobalt Blue	9009
	Yellow	9002
	Red	900
	White
NovaColor Artists Acrylic Paint Fluorescents	Fluorescent Blue	199
	Fluorescent Yellow	197
	Fluorescent Red	193
	Titanium White	118

There were three colors of each paint as delivered: red, yellow, blue, and each color was cut ~1/3 by volume with the same manufacturer's TiO2 white (except the fluorescent colors from NovaColor). The samples were painted out on 3 x 3” Masonite squares. (The Masonite had a smooth finish on both sides.) The squares were primed on all sides with Zinsser’s BIN Shellac Base Interior and Spot Exterior Primer/Sealer, a TiO2 based primer labeled as photostable, and then the colors were applied over the white until the base materials and primer were no longer visible. This took two to five coats. The Keim had to be painted on an inorganic surface so Jessica made 3" squares from backer board, a re-enforced cement material. The back and sides of the squares were sealed with a TiO₂ primer said to be photostable (it was not and failed; it began to chalk heavily after six months of exposure). As per the Keim’s manufacturing recommendation, the paint was applied on an unpainted surface.

One set of painted tiles remained uncoated, and six types of coatings were applied over the other samples:

Golden MSA varnish with the manufacturer’s UVLS (UV Light Stabilizers)

NovaColor varnish with and without CIBA HALS 777 (Hindered Amine Light Stabilizer)

Triangle Triloncatalyzed polyurethane “antigraffiti”

Paraloid B-72 with and without CIBA HALS 777

777 is an experimental additive package designed by Richard Wolbers containing a new, high-performance HALS from CIBA.

Each tile was marked with an identification number using a permanent black marking pen, which worked well except for the Keim squares where the chalking of the primer added difficulty to reading many of the black markings.

Each of the coating and paint combinations selected for the experiment was duplicated and kept indoors in a dark chamber to serve as a control for the experiment.

The experimental program hoped to model the rate and extent of deterioration in wall paintings potentially related to the following phenomena:

Deterioration related to the components of the paint matrix: supports, binders, pigments, or coatings. (Deterioration includes lightfastness, stability of the paint film, and photoreactivity.)

and

Deterioration related to its local environment: climate, humidity, or sunlight. (Deterioration includes flaking, molding, mechanical wearing, and fading.)

In the first year we took readings every three months, the second year every six months, and now in the third year we are taking readings once a year. Full results will be submitted for publication at a later date.

Some preliminary results after three years of exposure include:

Golden acrylics*

Golden paints have performed well, maintaining the intensity of their pigments; the reds faded the least out of the three colors. When cut by TiO₂ the tiles exhibited fading to a lesser degree than all acrylic paint systems, indicating that there is no harm in the artist cutting the factory Golden paint with Golden white, which expands the palette available to the mural artist.

Sher-Cryl HPA High Performance Acrylic*

Sher-Cryl paints performed well, and actually had the best non-coated appearance out of the four paint groups. Sher-Cryl blue and red showed little to no fading, whereas the yellow mixed with white had faded noticeably.

Keim mineral paint*

Keim paints performed well when coated. When left uncoated, yellow, blue, and red tiles all exhibited signs of flaking. Coating seemed to alleviate the flaking problem entirely. Flaking may indicate a non-optimal surface preparation.

Novacolor artists' acrylic polymer medium*

NovaColor paints performed best when coated, particularly in the system using the NovaColor paint with its manufactured NovaColor coating. Best results were obtained when painted without TiO₂.

As an observation, it appears that the Triangle coating reduced the growth of mold and accumulation of dirt on the surface of the tiles; no mold or dirt was visible on the Golden tiles that had been coated with Triangle. However, Triangle polyurethane does not comply with the conservation ethical requirement of “reversibility” as it cannot be safely removed without harm to the underlying paint film using current conservation methods.

Paint manufacturers are welcome to comment and offer helpful suggestions for the use of their products in regards to mural applications. Artists and others are also invited to write in with comments. Please address comments to our online forum.

[1] The paint colors were chosen from an artist’s perspective where the attempt was to visually match the same color paint from each manufacturer.

[i] Jessica Keister, Joyce Hill-Stoner, and Joseph Weber, “Paints and Coatings Used in Outdoor Murals,” in Modern Paints Uncovered. eds. Thomas S.J. Learner, Patricia Smithen, Jay W. Krueger, and Michael R. Schilling (Los Angeles: The Getty Conservation Institute, 2007), 284-5.