If you spend your weekends in museums you may become aware of another visitor who is behaving slightly oddly - a dark-haired woman who is quiet and decorous, but seems less interested in the exhibits themselves than in the display cases, the other visitors, and even in having a swift peek in the cleaners' cupboard.
You will have spotted May Cassar, environmental adviser at the Museums and Galleries Commission, and the person who probably knows more than anybody in the country about the relationship between buildings and the objects that are in them.
Spending her weekends in museums may smack of a busman's holiday, but she finds anonymous visits immensely useful. 'I like to watch other people's reactions, ' she says. 'I think architects could take a leaf out of that book and see how people respond to the spaces they are in.'
Cassar's own original training was not in architecture but, as well as growing into her present job, she did an MSc in architecture at the Bartlett on 'environmental design and engineering'. Covering acoustics, lighting, thermal environment and air quality, she found it 'gave a wonderful overview of environment'. But she was also shocked by the deficiencies in knowledge of her fellow students - all of them trained as architects. 'Architects' training in this country needs to be more technically robust.'
Her own knowledge is certainly robust, and she has carved out a role for herself through following her natural interests. Architecture was a love from an early age, but as she was taking the wrong A-levels she settled on history instead. During her holidays she worked for the National Museum of Archaeology in Malta, where she grew up, and grew interested in materials and their conservation. She won a Commonwealth scholarship to the UK where she took a BSc in conservation at the Institute of Archaeology, part of University College, London. Next: 'I decided I was still interested in the process of deterioration, in looking at the environment around objects.' She went to Rome for a year as a research fellow at ICCROM (the International Centre for the Study of the Restoration and Preservation of Cultural Property) studying the microclimate around objects, and the functioning of localised environments in buildings. This confirmed her interest in preventive conservation - something she equates with preventive medicine.
Cassar returned to the UK, and after some work for English Heritage became keeper of conservation at Foster's Sainsbury Centre at the University of East Anglia, where 'I really got more interested in buildings - that was the building that did it'. She also loved the collection's mixture of modern art and ethnographic objects, and spent 'five years of bliss' combining conservation with teaching art history students about care of collections. But she also became aware of ways in which buildings influence the condition of collections, especially of such diverse materials as those at Norwich.
She then taught for a while at the Textile Conservation Centre at Hampton Court before, in 1989, an opportunity came up at the Museums and Galleries Commission. 'It was the one job I have had sleepless nights over because I wanted it so badly, ' she said. MGC supported her course at the Bartlett, she wrote the bible on environmental management of museums, and her job has evolved to the present one, of educating clients and architects, through written guidance, courses and consultation on individual projects. She describes the MGC as having 'minimal resources with maximum impact' and says that 'before the lottery there were fewer new projects so it was easier'. But although she is rushed off her feet now, 'I don't want to work anywhere else'.
She has been able to carry out research, with current concerns including the effect of humidity and - those cleaning materials. Triggered by the discovery that one museum had used bleach on the floor around a bronze statue, causing the plinth to corrode, she is working on providing guidance on what should and should not be used in which areas of a building.
This is typical of Cassar's down-to-earth approach. She uses her wealth of knowledge and experience to look for the simplest, not the most esoteric, solutions. 'We can get very precious about objects, ' she says. 'We have to look at how we can pass them on to the next generation.' The important factor is balancing the needs of objects with those of people - after all, nearly every object would be perfectly preserved by keeping the temperature very low, but 'your visitors would get frostbite'.
Many museums are within listed buildings and there the rules are simple: 'The listed building must be the first object in your collection. To think about the environment in the space without thinking of the consequences to the building is anathema.'
There are 2000 museums in the UK alone, and she has consulted as far afield as Moscow. With so many potential places to visit, where is she most likely to spend her weekends? 'What I am most interested in are difficult combinations of materials, ' she says, 'in industrial and social collections, not 'high art'. Our understanding of how, for instance, metal and wood live together is interesting.' Any guesses as to the subject of the next authoritative piece of guidance?