On 12 December 2012, after completing the erection of scaffolding in Room 41, we were able to make an inspection during which, through close-up observation, we evaluated the state of conservation of structures and decorations.
We decided to make this a case study for the blog, taking readers through the phases of analysis, decision-making and consolidation work.
This room is representative of the Domus Aurea, difficult and complicated to resolve since many of the problems found in the whole complex are present within this single space. The cement core of the vault, consisting of pozzolana mortar and pieces of tufa, showed severe decohesion.
The decoration of the vault is missing a vast portion of the central area, cut diagonally by two sewers belonging to the Baths of Trajan above which run through the whole structure. This cut allows us to read the stratigraphy of the wall structure and the decorative system, as well as its state of conservation. The preparatory layers on which the painted plaster is laid is evidently detached from the structure of the vault.
On close-up observation we noted the presence of fibrous filaments, probably little roots and root hairs that have penetrated into the underside of the vault, lifting the paint layer and, in some cases, the preparatory layers as well. Blackening is not an absolute indicator of marcescence but may have a variety of causes: the root functions may have allowed fungal hyphae to grow on the innermost roots leading to blackening.
The presence of roots in the vault is caused by the primary nutritional structures of the Pinus Roxburgii which grows in the park on the Oppian Hill above and which may extend up to 35/40 metres from its position on the surface. The removal and laboratory analysis of a sample of the excrescences will provide a precise identification and evaluation of the vegetative state of the material.
A small group of technicians is at work to find the best solution for consolidating the decorated surface and the brick structure of the vault.