First up, a HUGE thank you to Emily and Louisa!!! Emily and Louisa have been part of the team since minute one. Other commitments beckon so they are taking a break from the fun and foibles of mosaic laying. We would like to say thanks and express our gratitude for their hard work and fantastic efforts in keeping the project kicking along. We don’t want this to sound too final, though. Emily is part of the Butser education team and is returning to duty after the school summer holidays, and Louisa is doing likewise at Bignor Roman villa. If you haven’t ever been to Bignor it is a really beautiful location with some of the finest mosaics… and staff… in Britain.
Despite the fairly obvious fact that we can see them(!), Romano-British mosaics are rather mysterious. We only part understand how they were made. We do know that the cement which supported them was lime-based. It contained aggregates like sand and small stones (just like modern concrete) but we have a relatively limited understanding of the makeup and mix of these materials. For example, the lime used to bind the concrete together came from heating material that contained plenty of calcium carbonate: limestones (including chalk) and sea shells, for example. One question is, how hot was the heating process? We understand how to heat lime in modern kilns but were Roman-style kilns as hot and did that matter? Did variations in making the lime lead to variations in the durability of the mosaic (probably!). What else went into the lime concrete mix…. That’s an interesting one. We know that terracotta (pots, tiles, bricks, etc.) was crushed and added to Romano-British concretes: it can be seen in broken period concretes and mortars and gives them a characteristic pink colour. Terracotta also has a ‘pozzolanic’ effect – that is, it strengthens the material.
Another interesting pozzolan comes from crushed volcanic stone, mined in southern Italy (including at Pozzuoli, near Naples and hence the name). It’s widely used in the Mediterranean and it gives immense strength to Roman concrete used in saltwater constructions. But was it used in Britain? The question becomes “what is it that helps ancient mosaics get ancient” ?!
To help us tackle this kind of technical challenge we are fortunate in our project in being able to call on advice from the Lime Centre in nearby Morestead. It’s where we get our supplies and the folks there have been very generous with their advice on materials, mixing and application. There is a caveat: our use of the materials, to bond a mosaic together and to the floor, is far from typical! And that brings us back to those questions about Roman materials science! Exactly what did they do and how did they do it?
And that isn’t the only mystery that our experiment is making us think about. A recent visit to Hadrian’s Wall, Vindolanda and Arbeia started some thinking… why do mosaics (and villas) seem to be concentrated in the south of what we now call England? Were the 10,000 troops on the Wall, living without the benefits of mosaic floors, really just collecting taxes?
It’s amazing what a mosaic project can start you thinking about.
For sites of villas and other really cool Roman stuff in Britain, have a look at this Archaeology Data Service site: http://archaeologydataservice.ac.uk/archives/view/romangl/map.html
By the way… if you haven’t been to Hadrian’s Wall, Arbeia or the fabulous Vindolanda – just go!
Emily and Louisa happily at work in the service of Romano-British mosaic reproduction