How Temperature and Humidity Impacts Your Collection
Updated: Oct 24, 2020
It's finally fall in New York City. I'm enjoying a respite from the hot, sticky days of summer and welcoming the cooler and drier days of autumn. I hope you are, too.
What better time than now to consider how seasonal changes and daily shifts in temperature and humidity affect your art, collections, furniture, antiques, photographs and family memorabilia at home.
New Yorkers experience wide fluctuations in temperature and humidity levels throughout the year. These fluctuations exacerbate the difficulty of controlling the environment inside our homes.
Unless you have central heat and air conditioning, managing temperature and humidity can be a challenge, especially for apartment dwellers. In cool months, forced air and steam-heated apartments are often dry and overheated, and many apartments don't provide occupants with thermostat control (a common complaint of those living in prewar buildings). In warm months, temperature settings on air conditioners may vary during the day. How often have you adjusted the temperature or turned off your air conditioners to save on energy bills?
So, how do swings in temperature and humidity affect your fine art, collections, furniture and property? They contribute to deterioration.
Temperature and humidity, along with light exposure and particulates, present the greatest environmental risk to your personal property and collections.
Don’t despair, there are things you can do. But first, let's understand why temperature and humidity is a problem in the first place.
Why Heat and Humidity is Damaging
Temperature affects relative humidity (RH), which is the amount of moisture in the air relative to the amount of moisture air can hold at a given temperature. And warm air holds much more moisture than cold air. Remember those hot, sticky days and nights just a few weeks ago?
Constant daily (even hourly) fluctuations in temperature and humidity cause expansion and contraction of the materials in objects as they adjust to a changing environment. Most objects are composed of more than one type of material, and every material responds differently to moisture in the air. Some more easily that others.
The problem is that changes in temperature and humidity (RH) cause internal stresses in objects, created by materials expanding and contracting as moisture is absorbed or released from the air. The most damaging conditions are rapid or wild fluctuations, not uncommon during hot summer days. So consider the following weather conditions and how they can impact your important property:
Low humidity (RH) leads to desiccation and embrittlement of organic materials.
High temperatures accelerate the deterioration of organic materials.
High humidity (RH) promotes the following forms of deterioration:
Physical: warping, dislocation of joints, splitting (wood), broken fibers, cracking and loss of surface material.
Chemical: corrosion, fading dyes, clouding or “weeping” (glass), salt crystallization (glass), disintegration and yellowing (paper).
Biological: mold growth (above 70% RH), bacteria and insect activity.
The following materials are most sensitive to high temperatures and moisture in the air. Unfortunately, they are also common in collections, and are frequently among our most valuable and cherished personal property:
Paper (e.g. works on paper, maps, manuscripts, books)
Plastics (commonly found in 20th century sports collections)
Metals (e.g. copper, brass, cast iron, aluminum alloys, zinc are more prone than platinum, stainless steel, silver, nickel, bronze)
Common Signs of Heat and Humidity Damage
So, how do you know deterioration is occurring from temperature and humidity? Watch for these symptoms:
Wrinkled, puckered or yellowed paper
Foxing on paper (brown splotches, patches or specks caused by mold/mildew interacting with metals present in paper)
Warped book covers
Split or warped wood
Fading, mold growth, tears and shrinkage in textiles
Clouding glass or “weeping” glass
Cracked emulsion on photographs
Stains on paper or prints
Cracked, brittle, warped, fractured or sticky surfaces on plastics
Corrosion on metals (see image above)
Now might be a good time to examine objects in your collections for these signs of deterioration. And always consult a trained art conservator for proper treatment or repair.
What You Can Do
Maintaining moderate and stable levels will significantly extend the longevity of important objects in your home. Try as best you can to create a stable environment by keeping the temperature and humidity constant throughout the year.
A good target in your home is a temperature of 70 degrees Fahrenheit and a humidity (RH) level below 55%.
If that's difficult or impossible to attain in your home (who doesn't like to open their windows?), here are additional recommendations:
Inspect works in your collection for signs of deterioration - continually.
Install window treatments (solar shades and insulating curtains) to reduce heat generated by sunlight during the day.
Avoid storing objects and works in an attic, basement, along exterior walls (which experience greater temperature fluctuations) or near heat sources.
Invest in archival storage containers and enclosures, which create tiny microclimates that mitigate temperature and humidity swings (purchase from archival suppliers).
Add silica gel packets (desiccants) to storage containers to absorb excess moisture (also from archival suppliers).
Monitor temperature and humidity in your home: Even inexpensive devices will give you a general idea of temperature / humidity changes throughout the day.
Consider climate controlled off-site art storage for particularly valuable or vulnerable works.
These recommendations are intended to be pragmatic and realistic for collectors. Taking some of these steps can help reduce the deterioration caused by swings in temperature and humidity and increase the longevity of the things you love - and that matter to you. You may want to read my blog post Controlling Light Damage, too.
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