Friday 29 April 2016

The Humidification Chamber: conserving photographs and documents

In January, we blogged about photographs we had recently acquired after they were discovered at the former Paulist Ministry Centre (previously the Catholic Information Centre).

The photographs were part of a poster entitled "1957-1958 Building the New Information Centre." Receiving this poster gave us an opportunity to practice some basic conservation and use our favourite device: the humidification chamber.

This inexpensive tool is remarkably effective for softening documents and photographs that have been rolled or creased so they can be flattened. Essentially, a humidification chamber is a sealed container that holds moisture, while preventing the documents from actually coming in contact with water.

In this case, we wanted to see if humidity would soften the glue that was used to adhere the photos to the poster board.

This was the original poster when it was transferred to the archives. There were twelve photographs glued to a banged-up piece of foamcore, along with some labels. The bottom photo was missing.

We appraised the contextual value of keeping the poster in this format: the glue and the foamcore were not archival quality; the poster was not particularly informative or aesthetically significant; it would require a large storage space. Therefore, we decided to remove the photos and discard the backing, but first we took this photo for reference.

Two of the photographs are duplicates: can you spot the matching pair?

When we first went through the humidification process, we used only the two duplicate photos to make sure it would work safely. After successful results, we humidified the remaining ten photos.

Here is our step-by-step process:

Step 1: Using a knife, cut the poster into smaller pieces containing the individual photos.

Step 2:
Seal the photographs in the humidification chamber.

The chamber is a closed container that holds humidity, while preventing the documents from actually coming in contact with the water.

Our chamber is made from a storage bin with cooling racks (used for baking) raised off the bottom and secured to the walls with zip ties. Photos are placed on the racks, an inch of water is poured into the bin and plastic sheeting is secured with masking tape to seal in the air. 
As the water slowly evaporates at room temperature, the surrounding air becomes very humid and the documents absorb the moisture.

Step 3: Let the humidity work its magic. Check on the material periodically.

Materials absorb humidity at different rates. The clear container allowed us to check for progress. Over the course of the day, the photographs buckled and pulled away from the backing, indicating that the glue was sufficiently softened.

Step 4
: Lift the photographs from the backing using a conservator's scalpel. In this case, they peeled right off.

Step 5
: Place the moistened items between sheeting to be pressed.

The photos were placed on Reemay, a polyester used as a support for drying materials because it's non-stick. This was important because the glue on the back of the photos was reactivated by the humidity and quite tacky. Paper towels were placed on top of the Reemay, as a blotting material to absorb moisture.

Step 6
: Press the moistened documents between so they dry flat. Leave overnight.

Step 7
: Remove dry material from the press.

Bonus: we discovered extra labelling on the back of the photographs which helped us to further identify, date and describe the items.

Step 8
: Rehouse and store the material.

The photos were placed in plastic sleeves, housed in acid-free archival boxes, and stored in climate controlled storage.

We have also had success using the humidification chamber for flattening rolled blueprints.  We do this specifically for architectural drawings that are crumpled, torn and brittle, which makes them very difficult to flatten for viewing.

Architectural Drawings Special Collection, ARCH 008 C

Fragile and damaged 1926 blueprints of Corpus Christi church, Toronto, are placed in the humidification chamber overnight.

The blueprints absorb moisture, making them pliable enough to be unrolled and pressed so that they dry flat. 

(In this case, scotch tape had been previously used in spots to repair the tears. Unfortunately, the humidity had little effect on the tape's adhesive. We decided to leave it rather than risk further damage by trying to remove it.  Never use tape on important records! Tape is the bane of archivists' existence.) 

After drying overnight, the flattened drawing is supported with museum board, interleaved with acid-free tissue and stored flat in an oversize archival box.

DIY humidification chambers can be made in a variety of ways. You can use a sink or nesting storage bins. Read more on how to make a humidification chamber


  1. Great examples and explanations. Terrific to see the process step by step via the photos. Thank you!