Alas, many "museums" are run badly, understaffed, under-funded, and subject to negligence and theft. So it's important to find a good museum, not subject to these issues.
In the art world, once an object is "accessioned" by a museum, it takes a special process to "de-accession" it for sale or other release. Many art museums these days are doing that to raise funds -- all-too-often to buy politically-correct and "woke" art to satisfy various claimants.
Unless a donor makes a special and specific contract with the museum, the museum has the power to do just about anything with anything in its collection.
At CHRS, a donor of an object or archival item signs a Deed of Gift. It reads:
"Please complete this Deed of Gift and return this form to "CURATOR" at the above address. I or we: [type or print name] have delivered and hereby convey, transfer and give to CHRS absolute and unconditional ownership of subject objects and/or images and/or recordings and/or writings and archives and/or books, magazines and ephemera and the like physical and/or intellectual property described below and on any attached sheets, together with all copyright (in all media by means or method now known or hereafter Invented) and associated rights and all other legal rights therein which I or we have now or may after-acquire and I or we acknowledge that CHRS may retain, collect, curate, copy, renovate, display, modify, analyze, disassemble, transfer, sell or dispose of the subject gift as it may think best. Please provide all available history and documentation of the object (please attach)."
So, trust the museum management, now and in the future, or don't donate to it. But consider that the alternative is usually the dumpster, or at best an estate sale dispersing carefully collected and often restored and conserved objects of great cultural, artistic and/or technical and engineering merit.
73 de Bart, K6VK ##
-- --
Bart Lee,K6VK, CHRS Archivist and Fellow, AWA Fellow, ARRL Liaison
Texts only to: 415 902 7168
{Bart(dot)Lee(dot)K6VK(at)gmail(dot)com}