Museums are facing a sort of Malthusian constraint — an explosive increase in the volume of their collections, coupled with a severe reduction in funding, fuelled partly by the current economic crisis. Collections cannot be increased indefinitely and sustained forever. So what happens when a saturation point is reached?

The Museum of Natural History at the University of Pavia in Italy is an example of how things can go wrong at such a tipping point. Founded by naturalist Lazzaro Spallanzani in the eighteenth century, the museum was dismantled in the 1930s in the face of financial and other pressures. The collection — including some of the first animal specimens preserved by taxidermy — was then dispersed across a number of sites in Pavia and the surrounding area.

A dynamic eighteenth-century exhibit of horse muscle anatomy from Pavia's Museum of Natural History. Credit: GIAMBATTISTA VOLPI (1752–1821)/ MUS. NAT. HIST., UNIV. PAVIA

This was an extreme solution, but museums must evolve. The goal of museums, to safeguard the evidence of important changes in the history of the planet and humankind, is an endless task. In response, they must be dynamic places, where the acquisition of objects is balanced by the planned deaccession or disposal of others.

Such an activity is at odds with the fusty image of a museum as a place where items are preserved in display cases or kept in storage. However, the disposal of materials demands care: whether justifiable or not, it is often highly controversial and can devastate an institution's image. From small civic archives to the vast Prado in Madrid, museums are the repositories of our collective past and identity, and that makes any broad discussion of disposal problematic.

Careful accession and deaccession policies are becoming increasingly important elements of museum management, whether local, regional or national — particularly in the current climate of reduced funding. In Italy, these policies are crucial. The country harbours 47 World Heritage sites, more than any other nation, and is home to 4,000 publicly registered museums, including some of the most important art collections in the world. But funds are shrinking, to the point at which the existence of some museums, and some of the country's most famous works, hangs in the balance. For example, in June it was discovered that Raphael's masterpiece The Marriage of the Virgin was endangered by water seeping through the walls of the Brera Art Gallery in Milan, owing to a lack of routine maintenance.

Yet strategic disposals, including long-term or even indefinite loans of museum pieces, are not being seriously considered by museums worldwide as a way to cope with the costs of maintaining full public collections. Museum authorities in Italy, as in many other countries, have elected to adopt such measures as reduced visiting hours rather than consider the disposal of selected holdings publicly and openly — perhaps fearing a public backlash. This is not, of course, to suggest that museums should sell holdings simply to cover the costs of routine maintenance; but it may be necessary for some to be realistic and open about the size of their holdings and the number of pieces that can be successfully exhibited.

To achieve a balanced ebb and flow of pieces in museum collections, the phases of accession and disposal need to be carefully evaluated and managed. Traditionally, curators tended not to limit the inflow of items — in some cases coming to resemble compulsive hoarders. Today it is common for curators, applying narrower and more demanding criteria in their selection of accessions, to refuse 90% of the offers made.

Although most donations may be turned down without damaging the public perception of a museum, disposal of materials that are already held is a different matter. In the United Kingdom in 2009–10, for instance, public outcry halted Southampton City Council's attempt to sell works by sculptor Auguste Rodin and British artist Alfred Munnings in order to raise money for a new museum dedicated to the RMS Titanic. Competing resources, and debates over the relative significance of pieces or collections, form just part of the criteria for deaccession. The views of museum audiences need to be factored in.

Debates over deaccession and disposal should be conducted transparently, accompanied by a clear public explanation and rationale, and should involve the views of all stakeholders — from museum staff to local authorities and concerned individuals. This way, the public's sense of ownership of prized local collections can be honoured.

In the 1980s and early 1990s, Canada's Glenbow Museum in Calgary, Alberta, successfully used such a process to transfer or sell around 30,000 inherited objects that were no longer relevant to its mission. This large-scale, strategic disposal of objects, including texts and ethnological and military-history collections, allowed the museum to sharpen its focus and release resources for other core sections. Importantly, the move was recognized as valid by the public. The distribution of pieces also boosted the value of the collections they joined.

Deaccession is never simple, and is not to be undertaken lightly. Hastily conceived action could mean big losses for future generations. But meticulously planned disposals for the right reasons are preferable to the disposal of an entire collection, as has happened in the past.

Happily, such disposals may not be the final curtain in every case. Spallanzani's great museum in Pavia may have a future. The collection — a once-cherished jewel of our city and country that has lain dormant for more than 70 years — was only disbanded, not permanently disposed of. We, at the University of Pavia, are about to begin the process of reconstituting a great part of the original collection for eventual display here, to grant a future to a vital window onto the past.