The 541 (Immediate Source of Acquisition) field has a subfield, $e, which is defined for "Accession number." This might be a better choice for the museum inventory number, since it would be more visible to users in the bibliographic record than in the holdings record.
Elizabeth O'Keefe
Elizabeth O'Keefe
Director of Collection Information Systems
The Morgan Library & Museum
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New York, NY  10016-3405
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>>> Nel ten Brug <[log in to unmask]> 4/21/2009 7:06:48 AM >>>
Dear all,

The Rijksmuseum Research Library, the largest museum library in the
Netherlands, is currently trying to map its data to MARC 21. We have only
limited MARC experience, and we have a particular problem: our library
collection is also a part of the museum collection. This means we have to
give every item its own ‘inventory number’. Are there libraries who have
this same obligation, and where in MARC do they place this number? Since
we are using KOHA, we have been using the KOHA item field tag 952$t (copy
number, in MARC this would be 852$t), but I understand this is used for
items with the same call number. Can someone please help?

Nel ten Brug
Library Co-ordinator
Rijksmuseum Research Library