Constraints on setting a standard for the museum environment

tim writes 2010-09-02:

Setting standards for the museum environment is bedevilled by the paradox that the optimal environment for artifacts, and natural history specimens, hardly ever coincides with the optimal environment for people in a museum. In a store, the environment can be closer to the optimal, but one then encounters the second problem which is that different objects, or even different degradation pathways for a single object, require different preservative environments.

To these two fundamental difficulties we have to add two others, which are practical. The first is the cost of maintaining the chosen environment, the second is the damage to the building through condensation from humidified air.

Finally we have the difficulty and expense of retrofitting existing museums and historic structures to our modern concept of what is right for the artifacts.

There are two barriers to formulating a logical and consistent environmental standard.

For nearly all organic artifacts, mechanical stability is best served by a fairly high relative humidity, around 60%. Chemical durability is best served by total dryness, since many degradation reactions require water.

For nearly all organic artifacts, chemical durability is greatly enhanced by low temperature: around -5C is probably cold enough to delay damage until cleverer people think of some better way, or until uncivilised hordes destroy our monuments.

Current standards for what temperature humans can be exposed to without legal compensation demand somewhere between 25C and 18C, according to country. So we will have one standard contradicting another about the environment in a museum, and even in storage buildings there is some human presence.

Looking back at previous attempts to solve the insoluble, we observe a tendency to fix the climate for humans, then add constancy for the sake of the artifacts. Constancy is what engineers claim they can attain, at any period in the development of climate control technology. There is an entirely separate ecosystem of academic nerds compiling and publishing tolerance limits for various classes of artifact. Some of these classes are not even material classes: anthropological skin objects apparently need different conditions to books with leather binding.

So what should we do?

We can start by being honest. Humans like to live in air at around 22C and are prone to thievery. So we can subject artifacts to around 22C but still hold a constant RH in their immediate surroundings by improving showcase design away from traditional joinery towards electron microscope containment standard.

Anything regarded as humidity sensitive is awarded such a showcase.

Fortunately, hardly any objects are temperature sensitive over variation which a human would endure, so temperature instability is self correcting: artifacts cannot complain over an extreme temperature but humans surely will.

So we are left with the relatively small number of artifacts which cannot long endure a human-friendly temperature. Colour photos for example. In a museum exhibition, we should learn to accept copies, with assurance that the original exists, so that accredited snoops can occasionally check the accuracy of the copy.

For storage we can propose two categories: as cool as can be achieved by near passive means. This is a complicated discussion, but in the UK it means an annual average temperature around 13C, which represents maybe a doubling of lifespan compared with the more famous objects sweating in a museum.

For the few very delicate objects we can resort to a cold store. There is surely no need to go below -10C. We have only Arrhenius modelling to justify cold storage, there are no measured values for degradation at that temperature, so let us stop there until more data arrives.

Now I have proposed three climate zones for artifacts. All that remains is to chose a zone for each individual artifact. I shamelessly borrow from the UK food industry `traffic light labelling'

Museum exhibition is red, being dangerous, and cold storage is green. Alternatively green is museum exhibition: you can proceed, red is cold storage: inaccessible except to well muffed employees. The orange we can then assign to the cool store. Or maybe that should be green, being the lowest energy solution.

Maybe its best not to be clever and just label the three environments warm, cool and cold.

A 'museum stable' object (warm) can without damage be put in the cool store and a cold store object can with only slow damage be put in the cool store.

Now we just need to try out the system with some random artifact types:

Pink Chinese porcelain: warm
Nitrate film: cool
Stinking acetate film: cold
Big old ship (Vasa): warm but RH stable. Oops, I forgot to divide the warm category into just warm and warm with constant RH in a showcase. Let us add a warm-m category. There is no need to subdivide the cool and cold - they will be at constant RH anyway (believe me - it's easy).
Hawaiian oiled grass girdle: cool
Mirabilite (a deliquescent mineral) warm-m
tin model soldier: warm but never cold, because of risk of recrystallisation.
Blu-ray DVD: probably cool but really unknown.

Which brings me to the huge 'don't know' category. This includes nearly all modern materials and nearly all modern art. It is not the duty of the standard to define the environmental sensitivity of materials, because it is not possible to do that with accuracy that is more than just defensive protection against future criticism.

David Baynes-Cope wrote a book advocating soluble nylon as a cure for many defects in paper artifacts. You can still read that book in a library; wrong advice preserved for ever. The history of conservation is not a sequence of successes and insights, more a fumbling with the latest wonder material from the chemical industry. Perhaps the exact advice on material sensitivity can be an ever changing list on the internet, open to anyone to edit. On a wiki like this.