The Structural Conservation of Panel Paintings

tion bottles and also connect the polypropylene piping joining the three

bottles. ASwagelok fitting is also inserted into a precisely cut hole in the

Aclar bag to allow the pipe to form a leakproof connection into the bag.

AT fitting with an on/offvalve is attached between the third bottle of

the humidification system (which houses the RH sensor) and the bag. This

allows the release ofthe nitrogen gas into the room atmosphere during

the balancing of the humidification system, to produce the desired level

of humidification ofthe nitrogen flow.

During the initial flushing at a high flow rate, the RH inside the

bag should be constantly monitored. An opening of15–30 cm is left

unsealed and open on the corner of the bag opposite the nitrogen inlet to

allow efficient mixing and flushing of the interior atmosphere without

pressurizing the bag (Fig. 8). This opening is heat-sealed after the desired

stable oxygen concentration is achieved.

M A T  I I 75

Valves for controlling amounts

of “wet” and “dry” nitrogen

Nitrogen bubbles

through water

“Dry” nitrogen

RH monitored

Nitrogen

supply

from cylinder

Humidified nitrogen

piped to bag

enclosing object

Figure 7
Humidification system for the nitrogen gas.

High flow rate

of nitrogen

into bag

15 – 30 cm of

seam left open

during purge

Figure 8
System for purging the encapsulating bag
with nitrogen gas to reduce the oxygen con-
centration to 0.1%.