1.20 Exposure of Artists' Colorants to Airborne Formaldehyde, Peroxyacetyl Nitrate (PAN) and (PAN Nitrogen Dioxide Ozone)
 

Daniel Grosjean and Associates

Daniel Grosjean
Edwin Williams II
Eric Grosjean
Period of Activity: 6/90 to 10/91

Project Abstract
Previous work by Cass at the California Institute of Technology demonstrated that some colorants used in artists' watercolors faded in the presence of ozone and nitrogen dioxide (project 1.8) as well as nitric acid vapor (project 1.10). This project extends that work by exposing the same colorants to peroxyacetyl nitrate (PAN), formaldehyde, and a smog oxidant mixture containing PAN, nitrogen dioxide, and ozone.

Primary Publications
Williams II, E. L., E. Grosjean, and D. Grosjean, "Exposure of Artists' Colorants to Formaldehyde and to Purified Air," Final Report to the Getty Conservation Institute, June 1991.

ABSTRACT-See following citation.

Williams II, E. L., E. Grosjean, and D. Grosjean, "Exposure of Artists' Colorants to Airborne Formaldehyde," Studies in Conservation, Vol. 37, N 3, 1992, pp. 201-210.

ABSTRACT-Thirty artists' colorants have been exposed for 12 weeks to 120 ppb of formaldehyde in purified air as well as to purified air alone (control experiment). These exposures were carried out in the dark at ambient temperature (19 2 C) and humidity (RH=44-52%). Color changes (L*,a*,b* and DE) were measured using a reflectance color analyzer after 1, 2, 3, 4, 6, 8, 11, and 12 weeks of exposure. Color parameters (x, y, X, Y, Z, L*, a*, b*, and DE) were also calculated from the 380-700 nm spectra, recorded with a reflectance spectrophotometer, of unexposed colorants and of colorants exposed for 12 weeks to purified air and to formaldehyde. Regression analysis of the two data sets indicated that color changes measured by these two methods were in excellent agreement (near-unity slopes, correlation coefficients > 0.99).

Exposure to either formaldehyde or pure air in watercolor paper resulted in little or no color change for all colorants tested including inorganic colorants, alizarin lakes, quinacridones, triphenylmethanes, indigo derivatives, arylamides, and natural colorants such as curcumin. Formaldehyde, which is ubiquitous in indoor air including museums, does not appear to be a major threat with respect to damage to colorants in museum collections.

Williams II, E. L., E. Grosjean, and D. Grosjean, "Exposure of Artist's Colorants to Peroxyacetyl Nitrate," Final Report to the Getty Conservation Institute, July 1991.

ABSTRACT-Thirty-one artists' colorants brushed on watercolor paper have been exposed for 3 months to 4815 ppb of the photochemical air pollutant peroxyacetyl nitrate (PAN) in purified air. These exposures were carried out in the dark at ambient temperature (202 C) and humidity (RH=4510%). Color changes (L, a, b, and DE) were measured every week by reflectance spectroscopy reflectance spectroscopy;.

Exposure to PAN resulted in little or no color change for all colorants tested including inorganic colorants, alizarin lakes, quinacridones, triphenyl-methanes, arylamides, and natural colorants such as curcumin. A brief comparison is made of artists' colorant fading resulting from exposure to several air pollutants including PAN, ozone, nitrogen dioxide, nitric acid and formaldehyde. PAN, which may be present in museum air in many urban areas of the world that are burdened with high levels of photochemical air pollutants, does not appear to be a major threat with respect to damage to colorants in museum collections.

Williams II, E. L., E. Grosjean, and D. Grosjean, "Exposure of Artists' Colorants to Air Pollutants: Reflectance Spectra of Unexposed and Exposed Samples," Final Report to the Getty Conservation Institute, October 1991.

ABSTRACT-Thirty-one artists' colorants were air-brushed on watercolor paper or coated on Whatman 41 paper and exposed to purified air (control experiment) and to purified air containing air pollutants that are ubiquitous in museum air. The pollutants studied included formaldehyde formaldehyde; (120 ppb), peroxyacetyl nitrate (PAN, 50 ppb), and a mixture of photochemical oxidants (ozone nitrogen dioxide PAN). These experiments were of 12 weeks' duration and were carried out in the dark at room temperature and ambient humidity (typically 202 C and 5012% RH).

In these experiments, color changes as a function of pollutant dose (i.e., the product of pollutant concentration and exposure duration) were recorded weekly or biweekly using a reflectance color analyzer (Minolta 121 Chroma Meter). The measured color changes were reported in units of DE, with DE obtained from the relationship DE2 = DL2 Da2 Db2. The parameters L*, a*, b* are the standard CIE 1976 coordinates for chromaticity (a*, b*) and brightness (L*). The Minolta color analyzer was calibrated using a white reflectance plate standard, and the light source was CIE illuminant C CIE illuminant C ;(pulsed Xenon arc lamp, 6774K).

At the completion of the artists' colorant exposures, it was deemed desirable to obtain more detailed and more precise color information regarding exposed and unexposed samples, namely the color parameters x, y, X, Y, Z, L*, a*, and b* calculated from the full reflectance spectra recorded on a research-grade instrument. Thus, color parameters for exposed and unexposed artists' colorants were measured again using a Diano Match Scan II reflectance spectrophotometer,with the spot size of the light beam limited to 7 mm using the small-area-view option (this reduces the signal-to-noise ratio and allows precision for a few percent in reflectance measurements). The instrument was calibrated using a standard white tile referenced to an NBS standard. Calibration and reflectance spectra were all recorded with the specular beam excluded. Reflectance measurements were made at 2 nm intervals from 380 nm to 700 nm. The amount of colorant in the unexposed samples was adjusted so as to yield an initial reflectance of about 40% at the wavelength of maximum reflectance. These colorant samples were the same as those previously studied, i.e., color change measurements had been made earlier on these samples using the Minolta color meter.

ABSTRACT-Thirty artists' colorants brushed on watercolor paper have been exposed for three months to 48 15 ppb of the photochemical air pollutant peroxyacetyl nitrate (PAN) in purified air. These exposures were carried out in the dark at ambient temperature (20 2 C) and humidity (RH = 45 10%). Color changes (L*, a*, b*, and DE) were measured every week using a reflectance color analyzer. Color parameters (x, y, X, Y, Z, L*, a*, and b*) were also calculated from the 380-700 nm spectra-recorded with a reflectance spectro-photometer-of unexposed colorants and, colorants exposed to PAN for three months. Regression analysis of the two data sets for colorants and for standard ceramic color tiles indicated that color changes measured by these two methods were in excellent agreement (near-unity slopes, correlation coefficients >0.99). Exposure to PAN, which may be present in museum air in many areas of the world that are burdened with photochemical air pollution, resulted in little or no color change for all but two (curcumin and basic fuschin) of the colorants tested, including inorganic colorants, alizarin lakes, quinacridones, triphenyl methanes, arylamides, and natural colorants. A brief comparison is made of artists' colorant fading resulting from exposure to several air pollutants including PAN, ozone, nitrogen dioxide, nitric acid, and formaldehyde.

Williams II, E. L., E. Grosjean, and D. Grosjean, "Exposure of Artists' Colorants to Sulfur Dioxide," Journal of the American Institute for Conservation, Vol. 32, 1993, pp. 291-310.

ABSTRACT-Thirty-four artists' colorants brushed on watercolor or cellulose paper have been exposed for twelve weeks to 93 5 parts per billion (ppb) of the air pollutant sulfur dioxide (SO2) in purified air. These exposures were carried out in the dark at ambient temperature and humidity. Color changes (L*, a*, b*, and DE) were measured every week using a reflectance color analyzer. Color parameters (x, y, X, Y, Z, L*, a*, and b*) were also calculated from the 380-700 nm spectra, recorded with a reflectance spectrophotometer, of unexposed colorants and of colorants exposed to SO2. Color changes measured by these two methods were in excellent agreement for both unexposed and SO2-exposed colorants (near-unity slopes, correlation coefficients >0.9).

Exposure to sulfur dioxide resulted in little or no color change except for one category of colorants, the triphenylmethanes basic fuchsin, brilliant green, and pararosaniline base. A second exposure to higher levels of SO2 (920 30 ppb) for two weeks resulted in little additional color change, if any. A comparison is made of artists' colorant fading resulting from exposure to several air pollutants, including sulfur dioxide, ozone, nitrogen dioxide, nitric acid, formaldehyde, and peroxyacetyl nitrate. Implications for colorant-containing objects in museum collections are briefly discussed.