The diorama, typically comprising “preserved organisms and painted or modelled landscapes” (Tunnicliffe and Scheersoi, 2010, p. 187), has been a mainstay of Natural History museums for well over a century. While they are often much maligned as old fashioned by many museum professionals, they continue to be popular with visitors and can be valuable learning tools (Tunnicliffe and Scheersoi, 2010).
My recent visit to the US as well as my own research have got me wondering about the essential ingredients of ‘diorama-ness’. What would a psychological schema of a diorama be from a visitor’s perspective? When does a diorama stop being a diorama?
I would suggest that the displays at the American Museum of Natural History would be the closest to the traditional diorama archetype.

Diorama at the American Museum of Natural History, New York. There is relatively little interpretation beyond the description of the region it depicts.
Traditional dioramas attempt to re-create a naturalistic setting as closely as possible. The back wall of the diorama is often curved to enhance the effect of a foreground and a horizon:

The sand in the foreground and the painted background merge together to create a distant horizon
The dioramas are the principal focus of the exhibition, with the surrounding areas kept in relative darkness:

View into the African Dioramas in the American Museum of Natural HIstory
By contrast, the mammals displays in the Smithsonian Museum of Natural History take a different approach. Rather than a sequence of identically sized and evenly spaced dioramas, the space is more open and varied in height and scale:

A general overview of the Mammals area in the Smithsonian Museum of Natural History
While backdrops are still used to evoke a habitat or setting, there is no attempt to make these look realistic. Rather, the multiple layering of two-dimensional images gave a ‘picturebook’ feel to the displays:

Picturebook dioramas – the animals’ habitat is eluded to rather than directly represented
The Smithsonian displays also sometimes showed multiple levels of the same scene, something I don’t recall seeing in the AMNH dioramas. For instance some dioramas included peepholes to see creatures hiding below ground:

Peep-hole displays showing life above and below ground. The label in the foreground asks “What does this coyote smell?” A beaver hides beneath.
While I’m happy to consider these displays as a version of a diorama, I wonder if other visitors’ interpretation is as flexible. Consider the Biodiversity Gallery at my research site, the South Australian Museum:

A view of the South Australian Biodiversity Gallery. Interpretation is via touchscreen rather than traditional labels.
As with the Smithsonian, these displays are a variation of the diorama archetype. While the displays have quite realistic foregrounds, these are set against a simple blue background:

A desert diorama. The blue is evocative of the clear blue skies of inland Australia, although this link is not made explicit.
Beyond the dioramas, there is further use of design to evoke the habitat – in the forests area, lighting combines with a ceiling feature to create an arboreal feel to the space:

The forests area of the SA Biodiversity Gallery
However, this effect is subtle for those not attuned to seeking out design features. It was not explicitly mentioned by most visitors who I accompanied through this space, suggesting they either didn’t notice it because their attention was absorbed by the displays themselves, or they didn’t think it was worth mentioning. (Some noticed a change in the feel of the space but couldn’t quite put their finger on what was different.)
Design concerns aside, do the displays in the Biodiversity gallery count as dioramas? In the words of one of my research participants:
It’s not even a proper diorama, because the background’s missing. . . .
Further probing revealed that the painted background on a curved background (creating the artificial horizon) was an essential part of the diorama ‘schema’ for this visitor. However she continued to use the word ‘diorama’ to describe the displays, presumably in the absence of a more appropriate word.
What are the essential ingredients of a diorama to you?
Reference:
Tunnicliffe, S. D., & Scheersoi, A. (2010). Natural History Dioramas: Dusty Relics or Essential Tools for Biology Learning? In Anastasia Filippoupoliti (Ed.), Science Exhibitions: Communication and Evaluation (pp. 186-216). Edinburgh: MuseumsEtc.