I'm posting this newsletter because it's so important to our safety as practicing artists. Michael Skalka, Conservation Administrator- National Gallery of Art, writes this newsletter and discusses materials that are of interest to artists. Scroll down to the bottom where he has an email address that you can subscribe to if you are interested.
Grammar of Color
Volume 6, No. 1
The Mystery of Solvent Safety
Greetings again. I must apologize for such a long hiatus from writing. However, so many transitions have taken place over the last several months that writing has had to take a back seat to other pressing demands. The conservation division has moved from the area it once occupied since the late 1970s to a new temporary space that will accommodate us for about two years while our former studios are reconfigured with new plumbing, heating/ventilation/air conditioning, electrical and safety systems. Once put back together it should serve the needs of the division for many years to come. We have also made a transition to new leadership in conservation and we are all settling into new work roles. To further add to the workload, I have taken on a project of refurbishing an 1880s Italianate style townhouse so my free time is spent painting with a roller rather than a small sable brush and my palette is straight from the commercial world of paint chips with dazzling room color ideas. The shift from a plein air paint box to a roller pan requires some adjustment. I am measuring usage of paint in gallons rather than squirts of paint from a tube onto a wooden palette.
Painting walls and ceilings with commercial paints has led me down new paths that did not exist the last time I did any major house painting. The somewhat new world of low VOC and no VOC paints offers fewer pollutants for house painters personally, the home environment and the planet as well.
We think of acrylic paints as not having volatile organic compounds (VOC) since they clean up with water and don’t have the harsh smell of mineral spirits. However many, traditional acrylic paints for walls as well as our artwork have a small percentage of volatile organic compounds that aid in the formation of a durable paint film. Some VOCs are coalescing agents that assist the acrylic polymers in melding together to form a continuous film. Think of it as a bit of solvent that melts the outside of each acrylic polymers and fuses it to an adjoining polymer. Other organic compounds contained in acrylic paints are not necessarily solvents but nevertheless are volatile in that they evaporate into the air after the paint is applied. Given the large surface area after fresh paint is rolled onto walls and ceilings, a substantial amount of VOCs are released quickly as the paint dries and beyond the initial drying stage for a period of time as these compounds work themselves out of the paint film.
With all this wall painting close at hand, the smell of the VOC exuding from the paint inspired me to think about solvents in a broader sense as they apply to artists. This is also where one of the major paradoxes occurs in the world of the art as it clashes with the worlds of chemistry and physics. To fully understand health and safety issues, one has to take an interest in topics far outside of the world of art.
Most artists I meet focus on making art using the media they choose to manipulate. Overall, I don’t encounter many artists who are extremely interested in the subtleties of the materials, especially the chemical and technical aspects of art products. The commercial side of the paint world does not reveal itself easily to anyone. I don’t believe that one should have to get a degree in chemistry or industrial hygiene in order to understand the list of benign or harmful materials in paint related products. It is a morass of confusing acronyms, a display of complicated testing and reams of nearly undecipherable numbers. While it is easy to throw up your hands and say that it is too complicated to understand, the consequence of ignoring some fundamental issues with materials of a harmful nature in paint products can end with some tragic personal health results. This is one case where ignorance is not bliss. Apathy or improper handling of certain materials can result in both short and long-term damage to one’s health.
The industry does not do the artist or homeowner any favors. Request a Materials Data Safety Sheet (MSDS) from a vendor or manufacturer of materials that contain hazardous products in them and see just how much of it is understandable, especially the critical parts. Knowing that solvents are not to be orally consumed, splashed on skin or inhaled in a closed room is just the beginning of the process of understanding how material safety sheets provide valuable information.
As with nearly all things art related, art materials are derived from the larger world of commercial products. Solvents in particular, are the companions for oil paints because they possess the special property that allows then to dissolve the oil binder in paints and to be the vehicle to both dissolve and spread certain resins classified as varnish. Unfortunately, solvents come in various types. Some are very powerful. Others are weak. Some evaporate quickly while others linger for extended periods. Some are outrageously toxic and some are not acutely dangerous, but they all share the common component of being harmful to some degree to human health and a pollutant to the environment.
This article is not a course on solvent safety or selection, but rather an introduction calling artists to create a protocol for personal health and the safety as well as those who work around them. Education is essential to understanding what to use and what must be avoided both in selection of solvents and ways to use them.
Here are a few important things to know about solvents in a general way. Read more for yourself and make educated judgments about what to use and how to use it to maximize your safety.
What are you buying? Two aids in making educated decisions about solvent purchases can come from vastly different sources. The Materials Data Safety Sheet (MSDS) provides identification information on what harmful components are contained in a solvent product. Thankfully, in an odd way, MSDS lists chemicals because they are considered harmful and MSDS sheet focuses on these hazardous components. It will not provide information on benign or proprietary materials contained in a product. The other helpful entity is the Chemical Abstract Service (CAS) number. Chemicals are cleverly identified by a unique numbering system so, despite the name of the product, which may be called mineral spirits, thinner, paint thinner, solvent, Stoddard Solvent, VM&P Naphtha, or by trade names, if you dig down you can find the CAS number of the solvent and identify it. A word of caution is in order. CAS numbers are not so precise to identify exact materials. Some variations exist. See the section below on more bad news.
What are its properties? Artists who are concerned with solvent working properties will examine how fast they evaporate, if they leave any residue or what materials they will dissolve. For solvent safety, the task is a bit more complicated. Fortunately, a federal acronym….I mean agency, and other institutions provide some meaningful safety data on solvents. The Occupational Safety and Health Agency (OSHA) publish volumes of information on materials used in our modern world. OSHA publishes a guide that focuses specifically on a measured amount of time and concentration of solvent that can be present in a space that will not cause long-term harm to a worker. That measurement is called the Permissible Exposure Level (PEL) and provides some indication of how much or little solvent in vapor form can exist within a workspace before harm is caused. Think of it as a gross indicator of the danger a solvent poses. A higher PEL means that more solvent can be in a workspace but still not cause harm. A lower PEL number implies that the solvent has more dangerous components in it and a work environment must maintain a low level of the solvent vapor in the air around a worker. The measurement is expressed in parts per million. Note that these levels of permissible exposure are extremely low from a standpoint of a person being able to detect solvent odor if they entered a workplace that stayed within permissible exposure levels of solvent concentration. Good air exchange is an essential factor in maintaining low exposure levels. Further, the use of personal respirators appropriate to the materials used, add to maintaining low exposure to solvents by people who work with them on a daily basis.
For example, many artists know that OSHA rates turpentine as having a PEL of 100 parts per million (ppm) exposure before long-term harm is caused. That means that if an environment exceeds 100 ppm the risk to health is increased. Odorless mineral spirits are generally rated around 200 ppm PEL for exposure. A few heavy hydrotreated Naphtha solvents are rated as high as 300 ppm for the exposure threshold. In a relative way, that makes them safer than turpentine because the ppm can be higher without causing adverse health risks. However, 300 ppm is not insignificant, allowing artists to ignore a concern for safety measures. An artist still has to maintain a studio space with proper air exchange using outside air as well as keeping the container holding the solvent closed as much as possible. It takes a concerted effort to provide good air exchange. Opening a window or two does not constitute adequate air exchange.
The bad news! I hate to break this to you after reading up to this point, but we artist as mere mortals have no way to measure the parts per million of solvents in an environment without complicated and expensive equipment. These measurements require testing gear that goes beyond what most of us would be willing to buy or spend to evaluate our studio space. So we just don’t know how many ppm fill our studios if we crack open a can of solvent and let the vapor escape into our work area. Further, we cannot rely on odor concentration thresholds (the strength of the smell of a solvent) to help us determine if we have exceeded the maximum ppm as indicated by OSHA guidelines. This is especially true when using odorless solvents. We all have different sensitivities to odors. Some strong odors are not indicative of high concentrations and some dangerous solvents are not particularly outrageous in odor but can be present in very high levels of concentration that could cause harm. So drop the idea that you can become a human gas chromatograph and know when a solvent has reached a concentration strong enough to cause lasting damage. Overall, we just cannot use the OSHA PEL ratings for solvents to assure we have a safe working environment in the presence of these painting materials. The PEL is just a rough guide to understanding relative harm a solvent can do to human beings.
More bad news! OK, so we can’t use our nose to detect dangerous solvent odor concentrations and monitoring/testing is too time consuming and expensive. The other disheartening information to share is that not all solvents are pure and unadulterated. A thought-provoking article in the American Institute for Conservation Newsletter by Alan Phenix discusses discrepancies in solvent safety labeling for products. The same Chemical Abstract Service number can have small variations in the list of ingredients that if broken down indicates a large percentage of one main solvent and smaller amounts of other solvents. In many cases, those smaller amounts in the mixture have far more harmful properties than the larger one and that will change the warning label on the solvent. Thus, two products labeled “Mineral Spirits” can have confusingly different PEL ratings. For example, a product I found labeled “Mineral Spirits” indicates that it contains both Stoddard Solvent and 1,2,4, Trimethylbenzene. The Stoddard Solvent is rated at 500 ppm PEL but the other ingredient is rated at an alarming 10 to 25 ppm PEL. The 1,2,4, Trimethylbenzene has such a low level of allowable concentration that this solvent is a hazard in a typical artists’ studio where ventilation is rarely up to industrial standards. Note that the label on the container says “Mineral Spirits” but it really is a mixture of two petrochemical distillates. Artists should not only look for high PEL rated solvents but also make sure that no other more toxic solvents are mixed into them. Understand that refining solvents is costly and that purer, more homogenous solvents require more effort/money to produce. While it is not suggested that you run out and look for reagent grade pure solvents, some careful reading when selecting solvents is in order.
In the case of solvents, cheaper is not better. Low cost solvents are more likely to contain adulterants that have very different PEL ratings than the primary ingredient. This is the part where ignorance can be very harmful to you and those around you. Be selective about your solvent choices and use the manufacturer’s research, MSDS data and reputation of the manufacturer as a guide to buying products.
The Orange Myth: The Internet is filled with references that promote the safety of solvents based on the oil extracted from the skins of oranges. What could be more wholesome? Orange citrus cleaners and environmentally friendly orange solvents are all marketed as alternatives to those bad, nasty hydrocarbon solvents. Some advertise the solvents as “food grade” in purity. However, referred to by the MSDS names, Orange Terpenes or D-Limonene, the concentration for Permissible Exposure Limits is a frightening 30 ppm. That is only 5 ppm higher than 1,2,4, Trimethylbenzene and nowhere near the level of highly refined Naphtha at 300 ppm.
Artists have many choices. They can use few if any solvent products and still paint with oil based materials. A system for working solvent-free has been well documented. Artists can also engage in various levels of solvent use from judicious to outrageous. Some think nothing of using open cans of solvent in poorly ventilated rooms. Others carefully use solvents and pay close attention to how long they keep any solvent open to the air. Either way, one rule about the universe prevails and that is the consistency of the physical properties of materials. It does not matter if you choose to become savvy about solvent use or carefree about exposure to them, the harmful effects will apply to everyone without regard to how much you care to learn about the subject.
So in closing, the caution is this. The harmful effects of solvents are not someone else’s problem to confront. It is yours. Art materials are derived from a technical world and you can choose to disregard the complexities of some rudimentary chemistry but you will pay the price at some point. Make the effort to learn how to handle solvents and how to select them. Learn what harm they can do to you, design a safe system that keeps solvent vapors at low levels so that you can reap the reward of what will hopefully be a far longer and productive painting career than if you choose to ignore the danger.
The Grammar of Color
Reflectance and Luminescence Imaging Spectroscopy of Paintings, Works on Paper and Illuminated Manuscripts
(Please note: This will be a technical lecture and is intended for an audience interested in analysis of works of art.)
Dr. John K. Delaney
Andrew W. Mellon Senior Imaging Scientist
Scientific Research Department
National Gallery of Art
2:00 PM, Tuesday Feb 16, 2010
West Building Lecture Hall
Abstract: Imaging spectroscopy, the collection of numerous calibrated images in narrow spectral bands, is a powerful technique for remote identification and mapping of materials. Using reflectance imaging spectroscopy, minerals have been identified and mapped on the Earth and Planets. Luminescence imaging spectroscopy is used in biophysics to follow complex cellular activity by separating and mapping various fluorescently tagged biomolecules. In this talk we present our group’s findings on the application of both forms of imaging spectroscopy for the identification and mapping of artists’ materials in paintings, works on paper and illuminated manuscripts. The results are compared with those obtained from X-ray fluorescence, polarized light microscopy and SEM/EDS. Imaging sensors employed in the study consist of novel hyperspectral (hundreds of spectral bands) and multispectral (15 spectral bands) cameras operating from 400 to 2400 nm. Results will be presented from the study of paintings, such as Giorgione’s The Holy Family, Picasso’s Harlequin Musician, Gorky’s Organization and Manet’s The Old Musician. Using high sensitivity spectral cameras, imaging spectroscopy has also been proven to be useful for the identification and mapping of artists’ materials in works on paper, such as those by Mark Rothko and John Marin and illuminated manuscripts, such as Christ in Majesty with Twelve Apostles from the workshop of Pacino di Buonaguida. These results show that combined reflectance and luminescence imaging spectroscopy in the visible and infrared is a powerful in situ tool for the identification of artists’ materials and that it can serve as a guide for the selection of sites for further chemical analysis.
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