UMCA Technical Leaflet
Zeolite Molecular Technology in Museum Quality Boards
For many years now, conservators have recommended the use of "archival"
matboards and paperboards for the preservation of artifacts and artworks.
These included matboards for works on paper and photographs, as well as
various types of paperboards for storage boxes and containers for artifacts.
"Archival" matboards and paperboards are specified as being
materials that are lignin-free (having no wood pulp component, most often
100% cotton rag board or high alpha cellulose content), sulfur-free (necessary
for silver artifacts and for silver-based photographic materials due to
possible sulfiding of the silver, which causes tarnishing, discoloration
and darkening), alkaline-pulped and containing an alkaline reserve (usually
a 3-5% addition of an alkaline chemical such as calcium carbonate). These
"archival" quality boards provided a high quality, safe storage
environment for the various materials that might be contained within them.
Due to further concerns regarding the preservation and conservation of
photographic materials, these boards were also supplied in unbuffered
forms (containing no alkaline reserve), as experience indicated that the
buffering chemicals could affect some photographic processes. These types
of "archival" boards have become the standard for use with museum
collections, but recent developments in technology have produced a new
type of paperboard and matboard that provides even greater protection.
This new technology developed in the early 1990's, makes use of zeolite
molecular traps. These are incorporated into conservation quality paperboards
and matboards under the trade name MicroChamber Products, which retain
their lignin-free, sulfur-free, alkaline pulped and alkaline reserves,
but have an added element”zeolite molecular traps. Prior to the development
of this new technology, "archival" paperboards and matboards
were not effective in neutralizing certain acidic pollutant gases. A study
at the National Archives and Records Administration in 1993 found that
certain pollutant gases, most notably sulfur dioxide, could pass through
"archival" paperboards and matboards affecting the materials
stored within them. The alkaline reserve or buffering agents incorporated
within the "archival" paperboards did not effectively neutralize
acidic pollutant gases. Other pollutant gases from atmospheric and environmental
sources or the by-products of deterioration must also be considered. Alkaline
gases and oxidizing gases can also diffuse through "archival"
paperboards in a manner similar to acidic pollutant gases. In these instances,
an alkaline reserve would do nothing to neutralize or eliminate these
types of gaseous pollutants.
Zeolite molecular trap technology targets gaseous pollutant sources and,
as pollutants are continuously increasing in our environment, have become
a preventative conservation priority. Gaseous pollutants come from a variety
of sources but some of the most destructive include automobile exhaust
containing nitrogen oxides, burning fossil fuels that contain sulfur dioxides,
oil-based paints that produce oxidizing gases including peroxides, and
wood materials used in construction that emit aldehydes including formaldehyde
and acidic gases including formic acid. Added to these are degradation
by-products that artifacts and artworks produce as they deteriorate. The
isolation, elimination or neutralization of these pollutant gases is necessary
to reduce their deteriorating effects. The use of molecular traps incorporated
within storage materials represents one solution to this problem.
Molecular trap is a general descriptive term for specific chemicals that
trap certain types of gaseous materials at the molecular level. Two of
these molecular traps are activated carbon and zeolites. Activated carbon
is inert, porous graphite, while zeolites are microporous crystalline
aluminosilicate structures that provide selective molecular trapping based
on size and polar properties of various chemicals. Activated carbon is
not practical in some museum applications, including matboards where the
graphite would appear as a gray line within the matboard and with cutting
or beveling could result in smeared graphite on an artwork. The advantage
of zeolites over activated carbon include the fact that they can be engineered
to target specific sized chemical species and that they can be used in
applications where activated carbon cannot because of its color or handling
problems. The crystalline nature of zeolite traps provides the inert,
non-reactive qualities that are required for proximity to collection artifacts
and artworks, while functioning to trap various molecular materials, in
particular, degradative gaseous chemicals present in the collection environment.
Zeolites are naturally occurring or synthetically produced aluminosilicate
minerals with three-dimensional structures that are linked to produce
an open structural form that has internal cavities in which molecules
of various sizes can be trapped. These internal voids, engineered to have
specific sized openings, can trap and hold a variety of molecules that
enter the structural matrix. The attractiveness of engineering a zeolite
lies in the ability to obtain specific properties such as water repulsion,
optimum internal cavity size, as well as several other physical properties.
Zeolites can be engineered to be acid resistant, which is most important
since acidic pollutant gases and acidic degradation by-products are anticipated
as components in a collection storage environment. Water repulsion is
important to prevent internal cavity sites from filling up with water,
reducing the number of cavities available to trap pollutant molecules.
While alkaline reserves in matboards and paperboards are incapable of
rendering acidic gases inactive, they are required to neutralize free
acids generated within paperboards, especially as deterioration by-products.
Alkaline buffers also support zeolites in cases where acidic gases associated
with the molecular traps react with water moisture in the paperboard to
form a liquid acid. This acid, should it become free, will be neutralized
upon contact with the chemical buffering agent. The presence of both zeolite
molecular traps and an alkaline buffering agent provide a solution to
the acidic components that might be present within the paperboard.
To date many comparative tests between "archival" matboards
and paperboards versus zeolite molecular trap matboards and paperboards
have been conducted with significant results. The zeolite molecular trap
boards have proven to provide superior protection for newsprint paper
artifacts, color lithographic prints, black and white negative film, black
and white silver gelatin photographic prints, color photographic prints
and animation cels in a variety of accelerated aging tests, as well as
natural aging tests. In testing, the zeolite molecular trap matboards
and paperboards have proven more effective in preventing discoloration
of inks and papers, including yellowing, browning, bleaching and other
color shifts, as well as sulfiding of silver and silver-based photographic
materials preventing tarnishing, discoloration and darkening. The use
of these new zeolite molecular trap matboards and paperboards are a major
breakthrough in technology for preventative conservation and protection
of collection materials.
Presently two companies are marketing zeolite molecular trap technology
museum quality boards under the trade name of MicroChamber Products. These
include Conservation Resources International, which produces an entire
series of paperboards, matboards, storage boxes, file folders, barrier
papers, mounting boards, corrugated boards, and etc., and Nielsen &
Bainbridge, which produce a zeolite molecular trap technology series of
matboards and mounting boards for framing and museum applications. These
new types of boards and products with the zeolite molecular trap technology
are not significantly more costly than the usual "archival"
ones, yet the potential benefits are extraordinary.
For more information and product catalogues contact:
Conservation
Resources International
8000H Forbes Place
Springfield, VA 22151
Telephone: (800) 634-6932
Nielsen & Bainbridge
Marketing Department
40 Eisenhower Drive
Paramus, NJ 07652
Telephone: (800) 927-8227
Information used in this article was published in the Conservation Resources
International, LLC catalogue from 1999, and from an extended article entitled,
"Zeolite Molecular Traps And Their Use In Preventative Conservation,"
by Siegfried Rempel in the Western Association for Art Conservation Newsletter,
Volume 18, Number 1, January 1996.
Article taken from UMCA's Collection's Care Network newsletter Issue 2,
2001 by Neil C. Cockerline, Director Field Services