To test the oxygen concentration within the encapsulating bag,
the authors used the battery-powered Teledyne oxygen monitor (Model
320P). The monitor can be placed inside the transparent plastic bag, per-
mitting the oxygen level to be read from the outside.
There are three methods for creating a low-oxygen environment:- The static system. This method is ideal for treating small objects,
especially paintings. No purging of air in the bag is necessary.
An estimated amount of an oxygen scavenger is inserted to
absorb the oxygen in the bag initially and then to maintain the
oxygen concentration at 0.1% for the fumigation period. - The dynamic system. An inert gas is used to flush all air out of
the bag by an initial high flow rate. When an oxygen level
of less than 0.1% is reached, the flow is reduced to the level
required to maintain the low-oxygen atmosphere during the
treatment period. - The dynamic-static system. The bag is purged with an inert gas
(as with the dynamic system), but when the oxygen concentra-
tion has been reduced to 0.1%, the flow of nitrogen is turned
off, and a predetermined quantity of an oxygen scavenger is
inserted. The small opening in the bag for the insertion of the
oxygen scavenger is sealed for the duration of the treatment.
The static system
The oxygen contained in the encapsulating bag is reduced to a lowcon-
centration by the use of an oxygen scavenger (Gilberg 1990; Daniel and
Lambert 1993). The commercially available oxygen scavenger Ageless,
which was used in this study, is described by the manufacturer as a mixture
offinely divided moist iron (ferrous) oxide and potassium chloride (Fig. 2).
Ageless is marketed in several different compositions that are used for a
range of applications. The type used in this study was Ageless-Z, which is
formulated to react rapidly and thoroughly with oxygen at an RH of 50%
(Lambert, Daniel, and Preusser 1992; Grattan and Gilberg 1994). Ageless-Z
is packaged in small, flat, paper packets and labeled as Z-100, Z-1000, and
so on, to indicate the milliliters ofoxygen that a single packet can scav-
enge. In most situations reported here, Ageless-Z-2000 was used. Because
it can scavenge 2 l of oxygen, this size of packet minimizes the number of
packets that need to be placed inside the bag.
When bags of Ageless are initially placed inside an Aclar bag, they
scavenge the oxygen component of the air in the bag. Any oxygen that
subsequently leaks into the bag must immediately react with the Ageless
to maintain the low oxygen concentration in the sealed bag—that is, the
leak rate cannot be greater than the rate of reaction of Ageless with oxy-
gen. The leak rate refers to the amount of oxygen that permeates through
the plastic into the bag.
This static system is ideal for panel paintings.
To treat an infected panel using Ageless, a bag is made out of
Aclar plastic film, leaving an unsealed opening for the insertion ofthe
Ageless packets. The Aclar bag should be constructed to be slightly larger
than the object, to allow for the decrease in volume caused by the oxygen
scavenging and to prevent any pressure from being placed on the painting
by the bag. Once the bag is constructed, its approximate volume in liters72 Hanlon and Daniel
Figure 2
Package of twenty-five sachets of Ageless oxy-
gen scavenger.