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Old 12-05-2017, 11:21 PM
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bvanevery bvanevery is online now
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preventing condensation, long term storage

I will have need to store my acrylic paintings for a few years, as I don't currently have my own place. I'll have modest if not perfect climate control available, i.e. a semi-finished basement. I've read about recommended packing materials, and ones to avoid.

I'm mainly confused about the potential for condensation. I consider the following to be strange advice:

from SpareFoot Blog:
Quote:
Wrap your paintings in material that protects from dust, scratching and bugs while allowing air to circulate. Tissue paper, breathable sheets or blankets, and foam are all viable options for protecting your artwork in storage. Avoid plastic wrap and bubble wrap, as these materials will block air circulation and trap condensation, leading to water damage.

from Art Squared art collection management:
Quote:
Then wrap it with a high-grade polyethylene. Wrap it completely around, like a Christmas present, covering the face and the back, and do all of the taping on the back side. Use packing tape, but don't overdo it. Don't seal the overlapping edges of the plastic; the idea is to provide a barrier against moisture, but to allow air to pass through. A work that is completely sealed in can develop condensation as it passes through different environmental conditions.

If work is completely sealed in airtight plastic, I don't see how it's going to "develop" condensation. It has whatever moisture was inside when it was sealed. Now, perhaps one could think one's using a barrier that's impermeable to moisture, but it really isn't. Or one could state with an impermeable barrier, and it could get punctured or degraded over time. But if it's really sealed and stays sealed, I don't get the claim that there would be condensation. Even if there was, like say all the trapped moisture moved to the top of the painting and then dripped in liquid form to the bottom, I'm not sure that's a problem if it has little moisture to begin with.

If a closed system stays closed, then I'm thinking you've got what you've got. What am I missing?

Why would people believe that an open system is superior?

Example: I make beef jerky. I don't use preservatives, so I have to refrigerate it. I guarantee you that I use an airtight container to do that. I'm not interested in the jerky "breathing", that would defeat the purpose of making jerky. Yes, any meat has some moisture remaining in it, or it would be the dry dust of the pharaohs. But when I seal an airtight container, no moisture is going in or out. It's got a locked gasket to stop that from happening. If I really really wanted to, I could vacuum seal the jerky in plastic bags.

A thought: is the basic problem, that people don't really know if their paintings are dry? Oils can take forever to dry. I do acrylics, but that involves a lot of water initially. Not sure to what degree they can retain or absorb water over time.

Or is the problem that people don't know how to make good seals? Tape isn't.
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Old 12-06-2017, 02:37 PM
contumacious contumacious is offline
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Re: preventing condensation, long term storage

You definitely do NOT want any plastic material touching the surface of your paintings. Virtually all plastic sheeting can adhere to fully dried acrylics. Personally I would not want anything touching the surface. If they are framed, you can use a sheet of cardboard that floats over the painting surface on the frame so you can then wrap them up well in plastic and add a desiccant pack.

Moisture is not a concern where I live so I store mine in dust resistant flat files or cabinets that have a moderate amount of air exchange. I don't allow anything to touch the front of the paintings.

If you need to control the humidity, you might look at building a box or getting a cabinet to hold your paintings with something in it that will keep the humidity low. A Goldenrod Dehumidifier is probably the easiest as it does not require an air tight container like silica gel does and it doesn't lose the ability to remove humidity like Silica Gel can if exposed to a continuous supply of moisture.

If you don't want to build or buy a cabinet, you can make an air tight enclosure that doesn't touch the front of your paintings, then the moisture absorbing materials would work. Just don't confuse oxygen absorbent packets with moisture absorbent packets like some do.

In a basement, particularly with an unsealed concrete floor, you would want to elevate the work off the floor.
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Old 12-06-2017, 08:15 PM
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Re: preventing condensation, long term storage

Quote:
Originally Posted by bvanevery
Even if there was, like say all the trapped moisture moved to the top of the painting and then dripped in liquid form to the bottom, I'm not sure that's a problem if it has little moisture to begin with.

The subject of condensation and relative humidity is complex. The devil is in the details, and there are possible corner cases I didn't consider.

For instance, artworks on paper are more delicate than acrylic paintings, and pools of moisture on the surface of such artwork would be very bad for them. I stumbled upon a Conservation Physics website, which gives grim details of what can happen to a printed work in an airtight enclosure. This makes me realize, I've made the unwarranted assumption that every part of my acrylic painting is strong, and will remain so, regardless of what pooled wetness it is subjected to. Over time, it could weaken somewhere.

Quote:
Why would people believe that an open system is superior?

Whether it is better to let a work interact with a potentially harmful environment (think of where a naive person might bring / leave your boxed work), or to leave the work "marinading in its own juices" is a complex question.

One issue I didn't consider, is that the work itself may contain harmful acidic gasses, such as if it's painted on wood. I'm not planning to paint on wood, currently Dibond is the leading contender for future work, but outgassing of volatile organic compounds is an issue to worry about. For instance, if one chooses some generic house brand of ACM panel instead of Dibond, and it turns out to be "made in China" with who-knows-what horrible stuff in it, maybe one could get into trouble.

When designing open systems, the conservators talk about "humidity buffering", and various materials which do or don't do that. This can include other artworks in close proximity to each other, especially in a museum context where storage space is at a premium. Can't now find the article where I read that; it's somewhere on the Conservation Physics site.

I think if I read piles of stuff on that site, I will eventually pretty much know what I should be doing. Or at least, I'll be well informed about the various issues. That's going to take some time through.

Quote:
Originally Posted by contumacious
In a basement, particularly with an unsealed concrete floor, you would want to elevate the work off the floor.

Aside from flood damage or water leaks, sources of thermal differential are something to watch out for. Conservators take the thermal effects of walls on the back sides of artworks pretty seriously, and this would apply to concrete floors as well. Thermal gradients induce condensation at the coldest part of the gradient. Meanwhile, the warmest part can be dehydrated.

Last edited by bvanevery : 12-06-2017 at 08:28 PM.
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Old 12-13-2017, 04:22 AM
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Re: preventing condensation, long term storage

After much reading, I found a 'recipe' for protecting a painting in transit. This is probably not identical to protecting a painting as it sits in an 'archive', as I believe the fellow who wrote the article, assumes that he can control the environment of the archive in various ways. The extensive 'recipe', does highlight a lot of issues that are simultaneously occurring.

Quote:
A rational design for a transport case for lightweight objects of considerable extent, such as paintings, would therefore consist of the following elements, listed from the inside out:

1. The object

2. One layer of paper for humidity buffering

3. Polyethylene film, wrapped around the object but not sealed, so that pressure change during a flight does not deform the wrapper. A reasonably well wrapped object will buffer its own relative humidity, because the air exchange will be slow during the flight.

4. Energy absorbing buffers to hold the painting physically in place.

5. An inner case to provide rigidity and also to provide the main thermal buffering. (If this case is of wood it should be coated inside with aluminium foil to prevent outgassing of acid gases).

6. Thermal insulation, typically medium density expanded polystyrene. This functions also as an absorber of knocks by sharp objects.

7. An optional lightweight outer case to enclose the polystyrene, to allow attachment of handles and messages to take care in many languages. This will also provide some visual authority, so that baggage handlers may treat the packet with respect.
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Old 12-26-2017, 02:14 AM
pschubert pschubert is offline
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Re: preventing condensation, long term storage

Thank you, bvanevery, for linking to my article, and for giving me the opportunity to clarify my recommendations.

First, I'd like to emphasise that the first sentence of the quoted paragraph in my article reads, "The best way to protect paintings is to make sure that none of the wrapping material touches the surface of the painting."

Now, about condensation:

All air contains a certain amount of moisture.

The amount of moisture air can hold depends on the air’s temperature. Warmer air can hold more moisture than cooler air. The more moisture in the air, the higher the relative humidity.

When warm, moist air makes contact with cooler surfaces, the moisture condenses, because the cooler air around the cooler surface doesn’t hold as much moisture as the warmer air. When the moisture condenses, it’s called condensation. When your car windows fog over, it’s a form of condensation, as it is when water collects on the outside of a chilled beverage.

There’s also a process called “vapour pressure,” which is the way humid air tries to achieve equilibrium by flowing toward drier air. This vapour pressure even forces the moisture through porous materials.

Because non-porous materials block the flow of moisture, condensation can occur on, underneath or between surfaces or layers.

Relative humidity will vary any time there are temperature fluctuations, weather changes, or air flow differences. This variance will affect artworks in situ and in storage, as well as artworks moving from one environment to another.

Wrapping artworks as described in my article permits the flow, or exchange, of varying relative humidities through the packaging, which prevents condensation from forming either on the inside of the packaging or on/in the artwork itself.


I hope this explanation is helpful. Thanks again for the chance to participate in this discussion.


Phillip Schubert, Principal
Art Squared
art-squared.com.au

Last edited by pschubert : 12-26-2017 at 02:23 AM. Reason: Fixed a typo
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Old 12-26-2017, 02:45 AM
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Re: preventing condensation, long term storage

Thanks! After all the digging I've done on the subject, somehow your explanation of these processes is more human readable. I wasn't clear on vapor pressure, for instance. Nor the role of non-porous surfaces in causing condensation. That explains to me why hikers like to wear various things to wick moisture away from the skin.
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