The Use of Commercial Paints in Museums


Preventive conservation covers a multitude
of initiatives to prevent damage to our cultural heritage by agents of deterioration. These include issues associated with the use of construction products and their potentially harmful effects on collections. There is often some doubt as to the use of
paint in museums. This problem has often been brought to my
attention by conservation professionals. Paint emits odours, and on several occasions in the past, paint fumes have been responsible for irreversible damage to museum objects. Two questions come back often: what paint should I use to avoid any damage to a collection? And how long should I let paint dry before
exposing objects to the painted surfaces? Although paint can indeed cause damage, fortunately this is happening less and less often. Now let’s take a look at hazardous conditions and how to prevent them. Pigmented coatings, varnishes and stains are used to paint walls and floors. They are also applied to structures such as storage cabinets, transportation crates and display cases. The level of risk depends on several parameters: risk will depend on the type of structure or wall to be painted on the type of paint
used on the time it is left to dry before the object is placed nearby. And the type of object placed there. Let’s
take a closer look at each of these parameters, beginning with type of structure. This will give us an idea of the amount of
surface to be painted in relation to the volume, and will give us an idea of the air exchange
rate for this location or structure. For example, are you looking to paint the
walls of a large room or the inside of a small display case? When paint is applied to gallery walls or
floors, the fumes usually disperse properly. They are cleared by the ventilation system
or open windows, or just disperse to other rooms. As a result, the risk of damage is low for
objects in this area. Conversely, in a hermetic space like a display case, paint fumes will build up and can reach high concentrations, possibly over a long
period of time. Such conditions can jeopardize objects in
this space. This makes it important to properly assess
the other parameters, which are: type of paint drying time type of object in the space. Let’s take a closer look at types of paint. Most of us are somewhat familiar with various types of paint. There’s oil paint, water-based paint, and maybe there’s more types than you think! Paints can be categorized based on the way their coating or film is formed. Here are the most common categories: there are paint films that are formed by coalescence by oxidative polymerization and by catalyzed polymerization. This classification may seem a bit technical, but it’s the key to distinguishing those that can be used for museum purposes and those to be avoided. Let’s begin with the first category: paints
that form a coating by coalescence. This is the emulsion paint commonly known
as “latex paint” in North America. This film is formed when water evaporates
and the suspended resin particles come together and coalesce. Acrylic is the type of resin typically used
for emulsion paints. It is sometimes mixed with other resins, such as urethane, styrene or even epoxy. When applied to wood, it provides an acceptable
barrier against its emanations. That’s why emulsion paint is often recommended
for use in museums. Next there are the films that are formed—or, more specifically, polymerized—through oxidation. This category includes oil paint, oil-modified urethane paint, alkyd paint, and epoxy ester paint. Epoxy ester paint is sold as epoxy paint and is available in a single can. You will see shortly that other types of paint are available in the form of two or three cans that need mixing. Never use paints that form a film through
oxidative polymerization inside a display case or on small, poorly ventilated structures. As they form, these coatings release acidic and oxidative compounds that can react with several types of objects. Fortunately, these coatings are becoming harder
to find in hardware stores because they do not meet new air quality standards. They generally emit too many environmentally
harmful volatile organic compounds; known as VOCs. One substitute for this type of paint is emulsion
paint. This paint emits fewer VOCs than oil-based
paints, although it still emits low levels. We’ve already mentioned coatings that are
formed by mixing two or three containers based on a very specific ratio. This is the category of epoxy or urethane
resins that polymerize using a catalyst or an active chemical agent. These very strong coatings are primarily used
on floors. Epoxy paints are chosen for their high level
of resistance to chemical spills, whereas urethanes provide good resistance to scratching
and abrasions. Epoxy and urethane coatings, which are formed
by catalyzed polymerization, are also recommended for museum use. We’ve just taken a look at the main types
of coatings. Many are acceptable, except those formed by
oxidation. It’s often hard to tell what type of resin
was used when looking at the label on the paint container. It’s even harder to tell how the coating
is formed. You can look up the technical and material
safety data sheets available on the Internet. Use keywords like alkyd, oil, oil-modified
urethane, and epoxy esters. These resins are usually formed by oxidative
polymerization and are to be avoided. So now we know which types of paint to choose
and which to avoid. The next point to consider is drying time. Even when using the recommended coatings, you need to pay special attention to drying time. Liquid coatings contain solvents, and when they are applied, the solvents are released. When the film forms, chemical reactions associated with this formation can also emit volatile compounds. After paint application, the emanation rates
for these volatile compounds diminish over time, as you can see in this chart. Low emanations are generally reached after
four weeks. It is therefore best to wait four weeks before
placing objects in a painted space. However, there is little advantage to waiting
longer than four weeks. There is little risk to objects when you use
the recommended coatings and leave a drying time of four weeks, even in an enclosed space. On the other hand, drying time for display
cases often represents a significant constraint for museums. Even when this time period is considered into
a new exhibit, any delay in the exhibit’s implementation often jeopardizes drying time. If drying time is less than four weeks, it
does not necessarily mean that objects will be damaged. However, the risk is greater. Often people only have two weeks. Two weeks is still better than only a few
days. For larger rooms or small, well-ventilated
rooms, a period of a few days is more than enough. These are areas where volatile compounds tend
to dissipate easily. One last point to consider is the nature of
the objects and their vulnerability to the volatile compounds released from coatings. Lead is the material most vulnerable to specific volatile compounds from coatings. These will cause it to corrode. Lead alloys or lead with a stable patina are
more resistant to acids. On the opposite end of the spectrum, lead
objects contaminated by some compounds, especially salts, may be even more vulnerable to acids. Given its sensitivity, lead can be affected
by acid emanations in an enclosed environment where there is wood or a recommended coating,
even four weeks after it had been applied. With a lesser risk, there is copper and its
alloys like bronze and brass. Acid and oxidative compounds from certain
coatings can also affect works on paper. Here, there will be no visible signs of deterioration,
but the fumes could reduce the paper’s useful life. In other words, the paper may yellow or become
friable earlier than expected. Other types of objects may also be affected by paint fumes, although there is no clear evidence. Nonetheless, caution should be taken. Along with a fair amount of explanation, we
have answered the two questions most frequently asked by museum professionals. We can summarize these answers in a few points:
avoid oil or alkyd paints or, in short, all paints that form a coating through oxidative polymerization. As a rule of thumb, choose emulsion paints, or latex paints. While there are few constraints for ventilated rooms, be careful with enclosed spaces such as display cases as well as with drying time. A four-week period is optimal to minimize
fumes. And remember! Lead will always be at risk where there is
wood and coating, even after four weeks. For example, in this photo, corrosion has
formed on small pieces of lead stored in a varnished wood storage unit. By following the recommendations described here, you will most likely be spared any unpleasant surprises. Now get out your paintbrushes!

4 Comments

  1. Sherif Afifi November 7, 2017 at 4:16 pm

    I used to ask myself which type of paint should museums use (from a preventive point of view); now your very informative video answers the question. Thank you for sharing

  2. Thierry Jacot January 4, 2018 at 10:39 am

    Merci pour cette vidéo très utile pour la formation des futurs collaborateurs en conservation…

  3. James Crawford March 17, 2018 at 5:03 pm

    great work, Jean Tétreault!

  4. James Crawford March 17, 2018 at 5:05 pm

    watch in 25 seconds the corrosion of lead metal by oak wood emitted vapours 2 years https://www.youtube.com/watch?v=28jxnee1IAc

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