A humidification chamber ‘made-to-measure’

The ‘tailors’ in this case were myself and Manfred Mayer from Graz, Austria, and we accomplished it all via email! I had started with a pretty clear idea of both what I felt was needed for our specific space at the Wellcome Library and the use that the preservation and conservation team was going to make of this piece of equipment, so I contacted Manfred, who looked after the technicality of it.

Our new humidification chamber, from my point of view, not only had to be used mainly in a specific area of our wet room, but also had to give us the flexibility of being used on our benches in the main conservation studio – or indeed in any other space of the building if necessary. It also had to be light enough to be carried easily to any of the places I have mentioned, and capable of being stored upright when not in use or if its normally assigned storage location was otherwise occupied. In other words, I was already pretty demanding before adding even more issues for Manfred to deal with, such as wanting the ability to control the amount of moisture and the amount of time within which I wanted it to reach (and hold, for as long as needed) a specific relative humidity.

Manfred and I exchanged quite a few emails regarding what I had in mind and how my wishes could be achieved. Nothing was too difficult for him to deal with, and he was always very positive and eager to come up with possible solutions. He even provided three different designs, which also involved differences in cost. The actual humidification chamber he made for us has the following the specifications:

• 1100x900mm stainless steel frame
• Height of frame: 60mm
• Height of hood: 200mm
• Weight: approximately 9kg
• 6 handles
• Acrylic tube for damp outlet
• Hood made of acrylic
• Device for keeping the frame open at an angle of approx 15°-20°
• Humidity Control Unit HCU
• RH-Probe
• Ultrasonic Humidifier, modified to be controlled by the HCU
• 1 hose (length 1,8m) plus 1 spare hose (length 3m)
• Travel adapter plug

The humidification system he built is ‘self-controlled’, which means that the closer the actual humidity comes to the desired value, the less vapour will be blown in. A blue light on the HCU (Humidity Control Unit) lights up when vapour is blown in.

The humidification does not stop completely, however, as there is always a small loss of humidity through the open area in the front of the frame (between the frame and the work surface), but the humidity inside the chamber will never exceed the desired value. The chamber’s dome contains a humidification sensor and some electronics that allow you to monitor the relative humidity inside the dome. The humidification sensor is the most important part of the control loop, and a self-testing electronic controller ensures that over-humidifying will definitely be prevented.

Manfred recommended that the dome not be completely sealed onto the worktop, as a perfect sealing around all sides is not desirable for using the chamber with an ultrasonic humidifier. On the contrary: a perfect sealing will prevent a constant, even flow of the humidity vapour.

Vapour is transported into the acrylic tube by a fan integrated in the humidifier. It is then blown into the chamber, but must leave the chamber via some small openings on the length side of the front, otherwise pressure builds up and, after some time, the vapour will concentrate in the nearest of the tiny openings of the tube.

The point of this system is that once you have done the setup and programmed the desired value, you can leave it alone. This allows you to humidify a paper very slowly, by increasing the desired humidity in small steps.

One final remark:

I also requested a system to keep the hood partially open for a single operator, and Manfred came up with a 5mm stainless steel rod to keep the dome open and allow manipulation of the object being humidified. He tried to find a very lightweight solution that additionally can be operated with one hand (you need the other hand for the handle to hold it open).

Although seemingly a little flimsy, these little ‘legs’ work well and they do what they are meant to be doing.

We have been using this chamber since 2011, and I cannot stress enough how beautifully it works and how easy and how safe it feels to use it. We went for the best and most expensive option but, as Manfred says, it doesn’t have to be so to work effectively. I just wanted to have the sturdiest option.

Manfred is very reticent about his achievement, but I feel that this piece of equipment should be introduced to other conservators. Having something that functions so incredibly well, and is tailor-made for one’s own needs and space, is hard to find.

Stefania Signorello ACR, Wellcome Library