My college George Bailey has the following points about the use of VCI's.
Kate is not I think talking primarily about archeological materials. In
Australasia our main concerns are modern materials and technological items.
I feel our approach may be a bit more scientific than many when it comes
to these items
Anyway here is Georges comment.
 
 
David Hallam
Senior Conservator of Objects
John Treloar Centre for Conservation Science
Australian War Memorial
ph  -61 6 243 4534
fax -61 6 241 7998
 
 
Hello Kate.
 
Re: VPI's. I did some studies on VPI's at UCan in 1990. There are several
things you need to consider when using VPI's, such as frequency of access
to storage, air tightness of the storage system, organic materials and/or
other metals in contact or proximity with the object, and of  course
temperature and RH.  The studies that I did included mild steel, not iron,
but I would expect that the behaviour of iron to VPI's would be pretty
much the same. VPI's can be expensive & I wouldn't recommend them as the
main means of protection in storage, but there are situations where the
very nature of an object, makes the use of VPI's more attractive than
other forms of storage. Metallic objects of intricate and complex
construction, where the application of a protective coating is not
feasible, are ideal candidates.  Note that VPI's need to be replenished or
replaced after 2 years or less, depending on how air tight the storage
system is. I suggest that you also look into dehumidified storage, as that
may be a more efficient system for a large number of ferrous objects.
 
At the Australian War Memorial we occasionally use VPI's for storage or
display. We have found Cortec VCI-560 and Shell VPI 260 to be the best for
ferrous objects, and Cortec VCI-307 the best for general protection of
other metals. The Cortec products are fairly safe as far as toxicity goes,
but I am not sure about Shell VPI 260, which is based on
Dicyclohexylammonium nitrite (DICHAN). I would treat it as toxic. Also
note that Shell VPI 260 will stain organic materials within its'
atmosphere. Mary Gissing (Museum of Applied Arts & Science, Sydney) did
some study on such effects, so I suggest you try to contact her. We have
not, as yet, tested the Senson range of VPI's, but they look promising
from their literature. Senson's Fax No. in Australia is (09) 478 2076
 
Feel free to contact me if you need any more information. Nice to see you
at the NZPCG/AICCM conference.
 
Cheers,
 
George Bailey.
Conservator of Objects
John Treloar Centre for Conservation Science
Australian War Memorial
ph  -61 6 243 4534
fax -61 6 241 7998